Radical Ideas or New Directions for AIC?

May 11, 2009

Thanks, Ellen, for letting me write a guest post on your blog.  The amount of conservation information you’re sharing here is impressive; I really can’t think of anyone who is putting as much treatment and research information out as you.  It’s as if you’re running your own conservation publication for the state of Alaska!

Also, I think it’s fascinating that you and I can be connected in a meaningful way without having met in person or chatted on the phone.  After all, you’re way up there in Alaska, and I’m here in Indianapolis.  To make this point visual, my friend, Tascha, in the IMA Photography department, made the image below.

Richard's Indianapolis Blog Cruise Stops in Alaska

Richard's Corn-Fed Blog Cruise Stops in Alaska

In recognition of the upcoming AIC Annual Meeting being held in Los Angeles that is dubbed “Conservation 2.0 — New Directions,” I thought it would be a good idea to put out some thoughts on “New Directions.”  Following this post, on Wednesday Ellen will be posting over at my home blog at the IMA and then on Friday Daniel Cull will posting at The Dan Cull Weblog.  We’ve all agreed to address potential “New Directions” for AIC.

Of course, to me, it makes total sense that I publish this post here in Alaska.  In many ways I think it is projects like Ellen’s blog that are beginning to change the landscape within the conservation profession and point to new directions.  I’m not just talking about starting a blog and telling people what you do, but it’s the capacity for anyone in the world to use a very powerful printing press basically for free.  The ability to share information about art conservation is changing dramatically.

Read the rest of this entry »


The Influence of Early Ethnographic Conservation in Alaska

April 3, 2009

The Objects Specialty Group Postprints. Vol. 10 Proceedings of the Objects Specialty Group Session.   American Institute for Conservation 31st Annual Meeting, Arlington, Virginia. June 8, 2003. 

The Influence of Early Ethnographic Conservation in Alaska.

By Scott Carrlee and Ellen Carrlee

*note: 2009 update at the end

 

The state of Alaska spans a terrain as wide as the continental U.S. and occupies one-fifth the landmass of the lower 48 states, yet contains a population only slightly larger than the District of Columbia.  Almost 60% of these people live in the three largest cities: Anchorage, Fairbanks, and Juneau.  The struggles of a small population in a vast land have always colored the history of the state.  Isolation has always been an important factor in the geographic and cultural development of Alaska.  A visitor behind the scenes in many small, remote Alaskan museums may be surprised, however, to find unusually good collections care, awareness and respect for preventive conservation, a long history of contact with conservators, and a sophisticated attitude toward the role of the museum in the community.  Certain key events contributed to those successes.

Civic consciousness paired with financial boom times influenced museum development in Alaska in the second half of the 20th century.  When statehood came to Alaska on October 18, 1959, there were only six museums in Alaska.  In 1967, the Purchase Centennial celebrated the bargain once called “Seward’s Folly.”  Alaska was purchased from Russia in 1867 for $7.2 million, the equivalent of $84 million today.  A federal block grant to the State of Alaska Purchase Centennial Commission was distributed throughout the state for community projects.  Many communities identified a need for local museums, and the number of Alaskan museums doubled during the events surrounding the centennial celebration.  In 1968, oil was discovered on the North Slope.  Construction began on the oil pipeline in 1974, and by 1975 the economy of state had doubled.  The first oil was pumped in 1977.  The Alaskan Canadian Highway (often called the Alcan Highway), built during WWII by the Army Corps of Engineers in response to Japanese attacks on American soil, underwent upgrades and improvements in the 1970s to support pipeline construction.  Improvements led to a boom in adventure tourism as well as opening up the interior to further settlement.  Alaska’s population grew by a third during that decade.  The 1976 United States Bicentennial celebrations raised national consciousness about history and the importance of preserving artifacts.  Many museums nationwide began to implement preservation policies and hire conservators.  Cruise ship tourism in Alaska was steadily on the rise in the 1980s, but exploded in the 1990s as a result of the Gulf War and American fears of traveling abroad.  By the end of the decade, tourism in the state increased by threefold.  

Today there are more than 60 museums and cultural centers in Alaska.  Even with the advent of “industrial tourism” the typical small Alaskan museum struggles to keep its doors open.  Admission tickets pay for only a fraction of the operating expenses, and the meager staff are often unpaid volunteers.  Professional training is rare.  The exhibits of these small museums can be hard to distinguish from the curio shops on every town’s Dock Street, hawking pseudo-Alaskan antiques and featuring bear skins and moose antlers on the walls.  Old-fashioned museum cases are over-filled with artifacts and memorabilia, often with a yellowed label typed on an index card.  

Behind the scenes, however, collections care, with an emphasis on preventive conservation, is surprisingly up-to-date.  Shelves are lined with closed-cell polyurethane foam, windows and lights have UV filters, gloves are worn, and objects tend to be securely housed.  The staff generally understands conservation and has specific ideas about what a conservator can do for them.  Indeed, 15 museums in Alaska (nearly 25%) have had Conservation Assessment Programs to date.  In 1990, during her time as conservator at the Alaska State Museum, Helen Alten conducted a conservation survey of the state.  She noted that over half the museums which responded had been visited by a conservator.  Over 80% stored their collections in acid-free materials and nearly 90% regularly sought conservation and preservation advice from the Alaska State Museum.  Today, there appears to be a unified conservation philosophy among the small museums of Alaska.  It is based on good fundamental collections care, preventive conservation and contact with professional conservators for advice and treatment when necessary.  This is remarkable, considering a grand total of only four conservators ever held permanent positions in Alaska before the year 2000.  What is the origin of this preventive conservation legacy?  Why did it stick so well in these museums?

The first big wave of conservation appears to have hit Alaska in the year 1975.  Bethune Gibson, head of the Smithsonian’s Anthropology Conservation Lab, was invited to the Sheldon Jackson Museum in Sitka to perform what seems to be the first general conservation survey done in the state.  Her report outlined the basic conservation condition of the collection, illuminated the environmental factors that were creating problems, and made recommendations for improvements.  It appears likely that her report, and the connection with the Smithsonian’s Anthropology Conservation Lab, led to the grant obtained by the Sheldon Museum to hire Toby Raphael as an ethnographic conservator for three months in the summer of 1975.  Raphael was studying at the George Washington University ethnographic and archaeological training program headed by Carolyn Rose, and internships at the Anthropology Conservation Lab were part of the program.  

Conservation treatments carried were carried out in a makeshift lab in the staff lounge of the Sheldon Jackson college library.  In his report at the end of the summer, Raphael noted that a large percentage of his time was devoted to the Eskimo mask collection since it was considered one of the most valuable in the museum.  

During the same period of time, one Alaskan was becoming increasingly interested in preserving collections.  Mary Pat Wyatt was the Curator of Collections at the Anchorage Museum of History and Art.  She was also working on a master’s thesis, “Problems in Conservation of Alaskan Ethnographic Material,” when she met Smithsonian conservator James Silberman.  Silberman was traveling with the “Far North” exhibition, a large exhibit covering 2,000 years of Eskimo, Indian, and Aleut culture that had been organized by the Smithsonian Institution.  He encouraged Wyatt to pursue an internship in conservation at the Smithsonian.  She contacted Bethune Gibson and organized an internship year at the Anthropology Conservation Lab starting in August of 1975.  This internship at the Smithsonian formed the backbone of her conservation education.  Wyatt returned to Alaska in 1976 to take a nine-month conservation position at the Alaska State Museum funded by the National Endowment for the Arts.  This was the first conservation position at any Alaskan museum, and remains the only conservation position in any institution in Alaska, despite the fact that both the University of Alaska Museum at Fairbanks and the Anchorage Museum of History and Art have considerably larger collections.  

Wyatt converted a darkroom in the basement of the Alaska State Museum in Juneau into a conservation laboratory and even managed to find a fume hood that is still in operation today.  Her primary concern, however, was outreach.  She visited 15 museums and cultural agencies around the state where she gave presentations and workshops on general collections care.  The following year the conservation position continued to be funded with another grant from the National Endowment for the Arts as well as a National Museum Act grant.  The focus of the lab continued to be statewide outreach.  Museums and cultural agencies around the state were invited to send objects to objects to Juneau for conservation treatment.  Three regional workshops were held in Juneau, Fairbanks, and Homer with a total of 68 participants.  Topics covered included grant writing, exhibits development, collections care, and preservation.      

In 1977, John Turney of the Valdez Heritage Center met Matilda Wells of the National Museum Act, who put him in touch with Caroline Keck of the Cooperstown Graduate Program in Conservation.  Arrangements for student interns to work in Alaska were discussed, but did not materialize.  

In the summer of 1978, four graduate students from the George Washington University/ Smithsonian Conservation program came to Alaska to do conservation work.  The National Museum Act provided the funding and Mary Pat Wyatt coordinated the work.  The four conservators were Alice Hoveman, Melba Myers, Susan Paterson, and Thurid Clark.  They worked in teams of two at four museums for one month each.  The four museums were the University of Alaska at Fairbanks, the Baranov Museum on Kodiak Island, the Sheldon Museum in Haines, and again the Sheldon Jackson Museum in Sitka.  In addition to treating the objects most in need of conservation at each museum, the teams also wrote reports providing recommendations for general conservation care of the collections.  The communities were impressed with the Smithsonian conservators, and there was local press coverage of the projects.  One of the students, Alice Hoveman, returned to Alaska after graduation to volunteer her time at the Sheldon Jackson Museum in Sitka.  The following year, Hoveman would take the position of Conservator at the Alaska State Museum following the departure of Mary Pat Wyatt.  Wyatt returned several years later to become the curator at the Juneau-Douglas City Museum, as position she held for almost 20 years.  

The State Conservator position was financed through grants until 1980, when a permanent full-time position was funded by the Legislature.  The nascent Conservation Services Program also had political implications.  Juneau was constantly striving to prove itself of service to the rest of the state in order to fend off attempts to move the capital closer to Anchorage.  Statewide outreach became a major mission of the Alaska State Museum.  Alice Hoveman presented a talk at the 1981 American Institute for Conservation Services Program.  According to Hoveman, 

“There existed a serious lack of understanding concerning preventive care for collections; i.e., inadequately controlled environments, limited security, and improper handling, storage, and exhibit techniques.  These conservation problems are complicated by the physical isolation and remoteness of Alaskan museums and the limited financial resources many Alaskan museum personnel are faced with.” (Hoveman, 1981)

The approach included on-site assessments, environmental monitoring kits and conservation literature available on loan, assistance for emergencies and disasters, and individual treatments for objects stable enough to be shipped to Juneau.  Hoveman also initiated the Museum Wise Guide, a booklet about collections care for Alaskan materials which included appendicies listing conservation suppliers and conservation-related organizations.  This booklet, funded by a grant from the Institute of Museum Services, has been distributed free of charge to Alaskan museums and cultural centers since 1985.  It is now in its revised second printing funded by the Institute for Museum and Library Services and is available on the internet.  Alice stayed in the position until February 1987, when Helen Alten took the position.  

In advertising jargon, people speak of certain campaigns having “legs,”  meaning that they achieve a longevity that goes beyond the initial appearance of the message in the media.  The conservation message that was carried by the core group of early ethnographic conservators in Alaska had “legs.”  The message seems to have gotten through and stuck with many of the smaller museums that had early conservation contact.  The message was carried on even with numerous staff changes.  We may never know why this is so, but a few ideas can be postulated.  

First, all of the early conservation participants during the formative years were trained at the same place, the George Washington University program led by Carolyn Rose, and/or the Anthropology Conservation Lab at the Smithsonian.  Second, the message was simple and effective.  It emphasized preventing damage and the fundamentals of good collections care, not the treatment of artifacts.  The concepts presented were meant to be understood by staff without specific conservation training.  Indeed, it may be that the museum workers lacking professional training were more receptive to this message.  Some of the larger, better-funded institutions in the state have not made conservation a priority, even today.  Third, the plans and recommendations could be carried out in the absence of continual conservator input.  The conservators came, but no one knew when they might return.  

Ethnographic conservation at its core is neither an art nor a science but rather a philosophy.  It is a philosophy firmly rooted in preventive conservation, and distinct from traditional fine arts conservation that is rooted in individual treatments.  The ethnographic conservators who studied at the George Washington/Smithsonian program were trained to care for large and diverse collections, to do the most good for the most artifacts with the resources available, and to look at the big picture before considering individual treatments.  

According to the National Needs Assessment Survey conducted by IMS in 1992, 75% of U.S. museums had a budget under $250,000 and are defined as small museums.  Most of these museums, like those in Alaska, do not have a conservator on staff.  Yet these museums house the majority of our cultural heritage.  Individual conservation treatments save individual pieces, often the spectacular and priceless ones.  But for the bulk of our historical material, it is the unspectacular realm of preventive conservation that will carry our treasures, great and small, into the future.  

Richard Beauchamp spoke at a museum workshop in 1976.  In his talk, he quoted Canadian conservator Phil Ward, and the words have great strength today as well: “Only the material specimens of humans and natural history are indisputable; they are the raw materials of history, the undeniable facts, the truth about our past.  Conservation is the means by which we preserve them.”

REFERENCES

Alten, H. 1993.  Results of the 1990 Alaska State-wide Conservation Survey.  Western Association of Art Conservators Newsletter.  15(3): 29.

Alaska State Museum.  1984.  Alaska Museums in the 80s: a Profile.  Juneau: Alaska State Museum.  

Beauchamp, Richard.  1996.  Unpublished talk delivered at the Museum Institute, Alaska State Museum, Juneau.  

Hoveman, A.R. 1981.  The Alaska State Museum Conservation Services Program.  American Institute for the Conservation of Historic and Artistic Works preprints of the papers presented at the ninth annual meeting Philadelphia, Pennsylvania, 27 April- 3 May, 1981.  Washington D.C.: American Institute for Conservation. 82-85.

Hoveman, A.R. 1985.  The Conservation Wise Guide.  Juneau: Alaska State Museum.  

Institute for Museum Services. 1992.  National Needs Assessment of Small, Emerging, Minority and Rural Museums in the United States.  A Report to Congress, September 1992.  Washington D.C.:  U.S. Government Printing Office.  

*UPDATE 2009

There are now thought to be closer to 80 museums and cultural centers in Alaska.  Some are new, and some small ones are just lately coming on the radar of outreach services at the Alaska State Museum.

Additional CAP assessments have been done in Alaska, perhaps at the rate of 2-3 per year, making he percentage of museums with assessments closer to 30% in 2009.

ADDITIONAL ETHNOGRAPHIC CONSERVATION INFLUENCE SINCE THE 2003 ARTICLE:

2001-2003? Melinda McPeek (2000-2001 Pre-program conservation intern, National Museum of the American Indian when Scott Carrlee and Ellen Carrlee had worked there) Museum of the Aleutians, Unalaska. Collections Manager.  Educational background in anthropology and art history, continued on in the museum field as a collections manager with an ongoing interest in conservation.

2002 Lara Kaplan (student, University of Delaware/Winterthur Conservation Program) Sheldon Jackson Museum, Sitka.  Birchbark canoe project, summer internship.

2001-2004? Sean Charette (don’t know his full conservation background, seems he went on to do work at the Getty and the Freer/Sackler) Museum of the Aleutians, Unalaska. Collections Manager.

2004 Dana Senge (student, Buffalo State Conservation Program) Yupiit Piciryarait Cultural Center and Museum, Bethel.  Collection care project, summer internship.

2007 Dana Senge (2006 graduate of Buffalo State Conservation Program) Baranov Museum, Kodiak.  Baidarka treatment project.  Sole proprietor, DKS Conservation in Seattle.

2007 Janelle Matz (2007 graduate of the University of Northumbria Preventive Conservation Program) Manager of the Contemporary Art Bank for the Alaska State Council for the Arts beginning in 2007. Had long been a collections manager at the Anchorage Museum, and had done some conservation treatments there as part of her work.   Had some early formal training…perhaps a Smithsonian internship?  Sole proprietor of ArtCare?

2007 Dana Senge (2006 graduate of Buffalo State Conservation Program) Baranof Museum, Kodiak.  Baidarka project.  Two weeks in March. Sole proprietor, DKS Conservation in Seattle.

In 2007, the Anchorage Museum of History and Art established a conservation position.  It was filled by Monica Shah, who grew up in Anchorage and received a Master’s of Science degree from the University of Delaware/ Winterthur Museum conservation training program in 1999 with a specialization in Ethnographic and Archaeological Objects.  Prior to accepting the position, Monica had run a private conservation business in Anchorage for several years.  In summer 1998, Monica, Ellen Carrlee, and Scott Carrlee all worked together in the lab of the Smithsonian’s National Museum of the American Indian in the Bronx, New York.

2007 Molly Gleeson (student, UCLA/Getty Museum Conservation Program) Alaska State Museum, Juneau and Sheldon Jackson Museum, Sitka. Basketry project.  Summer internship, presented paper at 2007 ICOM-CC Triennial in New Delhi, co-written by Samantha Springer, Teri Rofkar and Janice Criswell; also presented at the 2008 AIC conference.

2007 Samantha Springer (student, U. of Delaware/Winterthur Conservation Program) 2007 ASM, Juneau. Alaska State Museum, Juneau and Sheldon Jackson Museum, Sitka. Basketry project.  Summer internship, presented paper at 2007 ICOM-CC Triennial in New Delhi, co-written by Samantha Springer, Teri Rofkar and Janice Criswell; also presented at the 2008 AIC conference.

2008 Dave Harvey (apprentice trained, Professional Associate in AIC) Assessment of the Rapuzzi Collection for the National Parks Service.  Several days in fall 2008.  At the time, worked for Griswold and Associates in Los Angeles. 

2009 Jennifer Dennis (student, Buffalo State Conservation Program) Baranov Museum and the Alutiiq Museum in Kodiak.  Summer internship.

INTERESTING BUT NOT ETHNOGRAPHIC

1992 Vera Beaver-Bricken Espinola advised on treatment of Russian Icons in the Aleutians?  Published biography indicates she received a B.I.S. in Russian studies from George Mason University and an M.A. in museum studies with a concentration in ethnographic and archeological object conservation from George Washington University. She interned in the Anthropology Conservation Laboratory of the Smithsonian Institution. Fluent in Russian, she received an International Research and Exchanges Board (IREX) grant to study Soviet conservation techniques in Moscow, Novgorod, and Leningrad in 1980. A conservator in private practice in St. Petersburg, Florida, she has worked for museums such as the Smithsonian Institution, Hillwood, and the Timken Gallery, and for churches and private collectors as well as on exhibits, legal, insurance, and environmental problems concerning Russian icons and objects.

1998-2008? Cynthia Lawrence. Icon restoration project of Pribolof Islands, funded through restitution money from department of defense?

2001 John R. Kjelland (AIC member, in business as a furniture conservator since 1972.) Worked on the 46-foot historic Brunswick bar at the Valdez Museum.

2003-2007 Emily Ramos (1992 Library Conservation degree from Columbia University) Private conservation business in Anchorage, mainly working with the Rasmuson Library & Archives at Anchorage Museum. Managed the Contemporary Art Bank for the Alaska State Council for the Arts from 2005-2007.  Left Alaska for the job at the University of Berkeley Library system in 2007.2005 Tram Vo (2001 graduate of U. of Delaware/Winterthur Conservation Program) working at the UAF archives with Ann Foster to do an assessment of their photo collection.  Tram Vo Art Conservation, Los Angeles.

2009 Jennifer McGlinchey (student, Buffalo State Conservation Program) specializing in photographs, working with the Alaska State Historical Library and Alaska State Archives, also to travel around the state as part of  ARC (Archives Rescue Corps) and ASHRAB (Alaska State Historic Records Advisory Board) Summer internship.

2009 Grace White (2002 MA paper conservation, Northumbia University, England) Worked at Eagle Historical Society, UAF, and Barrow February-March 2009 to gain experience for Antarctica.


Summary of Potential Artifact Damage from Low Temperature Pest Control

April 3, 2009

The Textile Specialty Group Postprints: A Joint Session with the Objects Specialty Groups Concerning Composite Objects.  American Institute for Conservation 30th Annual Meeting Miami Florida, June 2002.

 

Summary of Potential Artifact Damage from Low Temperature Pest Control

 

Abstract

Preventive freezing for pest control during the relocation of the ethnographic collection of the Smithsonian Institution’s National Museum of the American Indian, Suitland, MD afforded the opportunity to undertake an observational study of the potential damage to vulnerable categories of materials and to investigate the possible causes.  The observational study revealed no visible damage to any of the materials frozen, although minor changes on a molecular level are likely.  Moisture issues are less of that threat than effects related to low temperature alone, such as shrinkage, embrittlement, and molecular alteration.  While many of these changes are reversible upon warming, the danger of cumulative effects from repeated preventive freezing of objects is questioned.  The conservation tradition of borrowing information from other fields proves difficult to apply to a low-temperature low-moisture content closed system.  This study contributes to an informed approach for the freezing of composite objects, cracked objects, lamellar objects, and waxy or oily objects.  Concepts of condensation, moisture content, concentration effects, glass transition temperature, coefficient of thermal expansion, polymorphism, lipid autoxidation, protein denaturation, ratcheting and shakedown are reviewed.  

 

INTRODUCTION

The Smithsonian Institution’s National Museum of the American Indian (NMAI) is in the process of moving its collections from facilities in the Bronx to the new Cultural Resources Center in Suitland, MD, just outside of Washington DC.  The old facilities had many insect infestations, and the current move protocol includes preventive low temperature treatment of most organic materials before entering the new facility.  Objects are sealed in a close-fitting polyethylene bag with padding and cooled below -20C for at least five days.  This situation afforded the opportunity for an observational study of the potential changes to ethnographic artifacts from low temperature pest management.

 

BACKGROUND

Several categories of artifacts are thought to be cause for concern at low temperatures.  One category is composite objects.  Materials generally not exposed to low temperature treatments, such as glass and metal, may be attached to materials appropriate to treat, such as wool.  Composite objects may also have built-in tension, and one material may restrict the movement of a different material.  A second category is cracked objects.  Concern here lies in possible propagation of the cracks or potential structural weaknesses implied by the presence of cracks.  Delamination of lamellar objects is another area of concern.  Examples include tooth and horn as well as layered constructions such as painted wood or adhesive systems.  The fourth category includes oily or waxy objects which sometimes demonstrate bloom or crystallization.  

 

DISCUSSION

The possible causes of artifact damage divide into those related to water and those not related to water.  Moisture-related issues include freeze-thaw cycling, dehydration, condensation, and swelling.  Conservation scientist Mary-Lou Florian has written extensively about these issues, but moisture remains a persistent concern for many museum professionals.  A well established understanding of damage from fluctuations in relative humidity (RH) leads to the extrapolation that artifacts may suffer from swelling and condensation in cold environments since RH increases as temperature decreases.  Standard operating procedure for pest management at low temperatures involves sealing the object in a close-fitting polyethylene bag with a buffering material such as tissue paper.  The total amount of moisture inside the bag is finite and in fact very low (Florian 1990ab, 1992.)  Buffering materials compete with the object for humidity the air can no longer hold, and porous organic objects have the ability to accommodate small increases in RH.  The bag itself prevents condensation on the object after removal from the freezer.

 

Experience in the kitchen also influences the understanding of organic materials at low temperature.  Water is critical to issues of food preservation.  Ice formation causes the 9% expansion in water volume responsible for freeze-thaw damage.  (Franks 1985.)  An increase in membrane permeability at low temperature causes loss of turgor pressure and wilting of fresh plant materials (Reid 1987.)  Removal of water from a solution via ice formation causes the remaining solutes to increase in concentration.  These so-called “concentration effects” can drastically alter pH, viscosity, oxidation-reduction potential, salt concentration, and enzymatic reactions (Taylor 1987.)

 

The fact of the matter is, most museum objects do not possess sufficient moisture content to form ice.  Most organic artifact materials in a museum environment have between 8% and 12% moisture content (Florian 1986.)  Artifact material with an equilibrium moisture content (EMC) of up to 28% does not form ice at the temperatures used for pest control (Zachariassen 1985.)  It is for this reason that some conservators avoid the term “freezing” and its implication of ice formation when discussing museum pest management.  It is also worth noting that many materials can take weeks or months to reach EMC at room temperature, and cold temperature tends to slow the process even further (Grattan and Barclay 1988, Howell 1996, Adelstein et al. 1997.)  The low temperature moisture content in the closed bag situation at approximately -20C is in fact rather unique and analogies are not easily found in the literature from other fields.  

 

Dr. Dana Elzey, research assistant professor of materials science at the University of Virginia, Charlottesville, VA consulted on the potential problems related to low temperature exclusive of moisture issues.  These areas of concern include shrinkage, embrittlement, thermal shock, polymorphic phase change, and molecular alteration.  Shrinkage may serve to counteract that small amount of swelling mentioned earlier.  Practically all materials shrink as temperature is lowered because of reduced vibration on the molecular level.  The coefficient of thermal expansion (CTE) is a measure of this change and is dependent on the strength of interatomic bonds.  Materials with weaker bonds, such as many organics, shrink more than those with stronger bonds, like metals.  At low temperatures, composite objects may be at risk for damage from “CTE mismatch.”  There are published tabulations for expansion coefficients on some common materials, but there may be no data for many materials in aged or altered condition, no data in the appropriate temperature range, or simply no data at all.  Often materials are simply categorized as high or low relative to each other.  During cooling, the low CTE material goes into tension and risks cracking or delaminating while the high CTE material is in compression and in danger of deformation or crushing.  CTE mismatch can also be seen within a single material, particularly one that demonstrates anisotropy.  The bonds in anisotropic materials are direction dependent and expand differently in different directions.  Examples include materials that tend to crack in a preferential direction, such as wood, bone, tooth and lamellar structures.  Cracking is not the only manifestation of CTE mismatch.  If the high CTE material is sandwiched between two layers of low CTE material, it may be extruded by pressure from the surrounding material.  While many materials have the ability to deform elastically and then recover, at sufficiently high stress some materials may lose the ability to deform elastically, resulting in non-reversible plastic deformation or failure.  

 

Embrittlement is another area of risk that may be reversible upon warming if elastic deformation is not exceeded.  Embrittlement occurs at low temperatures because molecules are resistant to motion.  The glass transition temperature (Tg) is an indicator of material flexibility.  Below Tg, applied stress may cause brittle fracture; above Tg, elastic deformation is more likely to occur.  Examples of materials that become brittle at temperatures used for pest control include rubber, oil paint, synthetic polymers, acrylic paint and soft vinyl (Michalski 1991.)  Vibration from a faulty freezer or rough handling before the object returns to room temperature are two sources of stress.  Embrittlement is usually reversible upon warming.

 

Any discussion of the risk of damage from shrinking should include an introduction to the terms “ratcheting” and “shakedown.”  Ratcheting describes the accumulation of plastic strain.  A ratcheting crack grows each time it is exposed to the same stress.  Damage evolution due to this kind of cycling is known as fatigue and will eventually lead to macroscopic failure.  The other option, shakedown, involves a reduction of the incremental strain per cycle.  Most of the damage in this process occurs the first time an object is opposed to stress, and each subsequent cycle results in less damage per cycle (Elzey 2001.)

 

Thermal shock is the condition in which rapid temperature change leads to excessive internal stress resulting in damage or failure.  It is the phenomenon that causes a hot ceramic plate to shatter under cold water.  Several factors influence magnitude of stress: overall change in temperature, rate of cooling, size of the object, coefficient of thermal expansion, elastic stiffness, conductivity, and strength.  Objects most at risk for thermal shock have high CTE, high elastic stiffness, low thermal conductivity, and low strength.  A large, rapid change in temperature increases the risk of thermal shock.  Although most organic materials possess high coefficients of thermal expansion, conduct heat poorly, and are held together by low-strength secondary bonds, they have the advantage of very low elastic stiffness and are comparatively resistant to the effects of thermal shock.  It is the inorganic components of certain composite objects that are of concern here.  

 

Polymorphic phase change is another factor to consider in low temperature pest management.  Phase change involves a change in state, such as from solid to liquid or liquid to gas.  Polymorphic phase change involves a solid-to-solid phase change from one crystalline arrangement to another.  In some cases, one polymorphic phase may be more stable than another at low temperature.  Tin disease is one such example.  At room temperature, pure tin is a shiny white metal.  As temperature decreases, a non-metallic crumbly gray powder becomes the more stable form, reaching a maximum stability at -30C.  Tin disease is inhibited by most of the common alloying metals used with tin.  Most of the museum’s tin artifacts, such as cone tinklers on Native American artifacts from the Great Plains, are alloys and therefore safe from polymorphic phase change in the freezer.  However, the textbook example of tin disease involves Napoleon’s attempted 1812 winter invasion of Moscow, which failed in part due to the disintegration of the pure tin buttons on the soldiers’ clothing.  Low temperature is also a factor in structural change because some materials, such as rubber and some fats and waxes, become crystalline at low temperature.  This phenomenon seems to be at least partially reversible upon warming (Baker, 1995.)

 

The final area of concern addressed here is molecular alteration, particularly regarding protein denaturation, lipid autoxidation, and loss of moisture regain in materials demonstrating hysteresis. Conformational stability in protein is dependent on a complex energy balance involving a variety of intermolecular forces.  Cooling weakens some forces, such as hydrophobic interactions, but enhances others, such as hydrogen bonding (Taylor 1987.)  The technology to study proteins at low temperature in the absence of ice formation has only been developed in the past decade.  The formation of ice and the concentration effects that occur when water is removed as ice forms continue to be at the center of scientific research, making the question of permanent denaturation of proteins from low temperature alone difficult to resolve (Taborsky 1979; Fahy 1995; Franks 1995.)

 

The Arrhenius equation states that the rate of chemical reactions tends to slow with decreasing temperature.  The oxidation of lipids is sometimes an exception.  Lipids contain a wide variety of fatty acids that differ in chemical and physical properties as well as their susceptibility to oxidation.  Some follow the Arrhenius equation and oxidize more slowly at room temperature.  However, low temperatures can accelerate autoxidation of unsaturated fatty acids (Karel 1985.) Mechanisms for this are frequently described in the literature as “enzyme-catalyzed.”  Since enzymes are proteins produced by living organisms functioning as biological catalysts in living organisms, it is doubtful that there are any active enzymes remaining in museum artifacts.  

 

“Because enzymes function nearly to perfection in living systems, there is great interest in how they might be harnessed to carry on desired reactions of practical value outside living systems.  The potential value in the use of enzymes (Separate from the organisms that synthesize them) is undeniable, but how to realize this potential is another matter.”    (Roberts and Caseiro 1977.)

 

Furthermore, solute concentration effects that allow enzymes and substrates to come into contact influence some enzymatically-catalyzed oxidation in lipids (Reid 1987.)  Museum objects that cannot form ice are not subject to concentration effects. 

 

The loss of moisture regain ability due to changes on the molecular level is another potential concern.  Many organic materials are able to absorb and desorb moisture to keep in equilibrium with environmental humidity.  Taking up moisture brings them to a more stable energy state and generally occurs faster than desorption, as the material is reluctant to give up that moisture.  This relationship between water activity and moisture content is illustrated by a sigmoidal curve known as the moisture sorption isotherm.  For example, room temperature wool at 55% RH has a lower moisture content if it is in the process of getting wetter than it does under the same conditions if it is getting drier.  At low temperatures, molecules with potential water-holding sites may draw closer together and bond, creating a reduced capacity to hold water in the future.  (Timar-Balazsy and Eastop 1998.)  The conservation literature suggests there may be a distinction between damage from long term cold storage and short term low temperature exposure for pest control (Wolf et al. 1972; Williams et al. 1995; Pool 1997.)  

 

CONCLUSIONS

Exploration of the literature and consideration of materials science issues raise two areas of concern.  One involves the likelihood of repeated freezing cycles for some objects, particularly those actively loaned or exhibited and therefore subjected to low temperature treatments with each re-entry into the museum collection or new venue.  Data involving wood (George et al 1992; Erhardt et al. 1996;) textiles (Holt et al. 1995; Jansson and Shishoo 1998; Peacock 1999), synthetic fishing gear (Toivonen 1992;) paper (Bjordal 1998) and insect collections (Rawlins 2001) suggest no significant structural damage with repeated low temperature treatment for pest control.  Theoretically, however, embrittlement, shrinkage, and thermal shock have the potential to cause damage if the limits of elastic deformation are exceeded, or if ratcheting occurs within the elastic range and leads to fatigue (Elzey 2001.)

 

The second area of concern involves the permanent physical changes that are likely to occur (and perhaps accumulate) on a molecular level but remain invisible to the naked eye, such as loss of strength, loss of elasticity, distortion, crystallization, molecular alteration, protein denaturation, and loss of regain ability.  In some cases there may be synergistic effects in which interrelated damage mechanisms combine to cause further problems.  

 

In summary, it might be helpful to state this information plainly.  Based on this investigation which involved freezing several hundred artifacts, reviewing the literature, and discussing the topic with many museum and scientific professionals, a list of factors has been prioritized from highest-to-lowest concern.  On the whole, low temperature pest control appears to be safer for artifacts than might have been suspected.  

 

1. Freeze-thaw and dehydration should not occur because there is not enough moisture in museum artifacts.  

2. Condensation should not happen if artifacts are bagged properly.  

3. Swelling probably happens a little bit, but not much because there is so little moisture inside the sealed bag.

4. Polymorphic phase change does happen with some materials, usually fats and waxes, but this is usually reversible upon warming except in rare cases such as tin disease.

5. Thermal shock is not an issue for most organics because the temperature change is not drastic or sudden enough.  Inorganics are at greater risk, but no reports of this kind of damage were found.

6. Shrinkage undoubtedly occurs, but at this temperature it’s fairly minor and perhaps counteracted by the small amount of swelling.  The reason it is placed higher on the list is because of CTE mismatch danger.  Drums are one of the few objects not frozen at the NMAI.  

7. Embrittlement is also very likely to happen, but is usually reversible upon warming and objects are mainly at risk from vibration or rough handling until they warm up.

8. Molecular alteration is a bit of a wild card.  Protein denaturation may occur, but it may be reversible upon warming.  As far as lipid autoxidation goes, this may not happen at all without enzymes and sufficient moisture content.  Loss of moisture regain ability appears to be more of a danger with long term cold storage.

 

ACKNOWLEDGEMENTS

Thanks to Dr. Dana Elzey, department of Materials Science and Engineering at the University of Virginia, and the staff at NMAI, including Marian Kaminitz, Emily Kaplan, Jessie Johnson, and Leslie Williamson for their support and feedback.  I would especially like to acknowledge Mary-Lou Florian for her excellent work on this topic.  Thank you to the Andrew W. Mellon Foundation for making this research possible.

 

REFERENCES

Adelstein, P.Z., J.L Bigourdan, and J,M, Reilly.  1007.  Moisture relationships of photographic film.  Journal of the American Institute for Conservation 36(3):193-206.

 

Baker, M.T. 1995. Ancient Mexican rubber artifacts and modern American spacesuits: studies in crystallization and oxidation.  In Materials issues in art and archaeology.  vol. 4, ed. P.B. Vandiver et al.  Pittsburgh: Materials Research Society. 223-232.

 

Baker, M.T. 1995. Thermal studies on ancient and modern rubber: environmental information contained in crystallized rubber.  In: Resins: ancient and modern.  ed. M.M. Wright and J.H. Townsend. Edinburgh: Scottish Society for Conservation and Restoration. 53-56.

 

Bjordal, L. 1998.  Effects of repeated freezing on paper strength.  Proceedings of the third Nordic symposium on insect pest control in museums.  Stockholm, Sweden: Naturhistoriska Rikmuseet. 54-56.

 

Elzey, D.M. 2001. The effects of thermal cycling on the structure and properties of solids.  Lectures given at the National Museum of the American Indian Research Branch, Bronx, NY and Cultural Resource Center, Suitland, MD.   Department of Materials Science and Engineering.  University of Virginia, Charlottesville, VA.

 

Erhardt, D. M.F. Mecklenburg, C.S. Tumosa, and T.M. Olstad.  1996.  New versus old wood: differences and similarities in physical, mechanical, and chemical properties.  In ICOM Committee for Conservation preprints.  ed. J. Bridgland.  11th Triennial Meeting, Edinburgh, Scotland. Paris: ICOM. 903-910.

 

Fahy, G.M. 1995 Cryobiology: the study of life and death at low temperatues.  21st century medicine.

 

Florian, M.L. 1986.  The freezing process: effects on insects and artifact materials.  Leather Conservation News 3(1): 1-4.

 

Florian, M.L. 1990a.  Freezing for museum pest eradication.  Collection Forum 6(1):1-7.

 

Florian, M.L. 1990b.  The effects of freezing and freeze drying on natural history specimens.  Collections Forum 6(2):45-52.

 

Florian, M.L. 1992. Saga of the saggy bag.  Leather Conservation News. 8:1-11.

 

Franks, F. 1985.  Biophysics and biochemistry at low temperatures.  Cambridge: Cambridge University Press.

 

Franks, F. 1995.  Protein destabilization at low temperatures.  In Protein Stability. ed. D.S. Eisenberg and F.M. Richards.  Advances in Protein Chemistry 48.  New York: Academic Press.  105-139.

 

George, M.F., B.C. Cutter and P.P.S. Chin. 1992. Freezing of water in hardboard: absence of changes in mechanical properties.  Wood and Fiber Science.  24(3):252-259.

 

Grattan, D.W., and R.L. Barclay.  1988.  A study of gap-fillers for wooden objects.  Studies in Conservation.  33(2):71-86.

 

Holt, L., Y. Chen and W. Dodd.  1995.  The effect on wool fabrics of multiple freeze/thaw treatments for insect control.  Textile Conservation Newsletter 29:28-35.

 

Howell, D. 1996.  Some mechanical effects of inappropriate humidity on textiles.  In ICOM Committee for Conservation Preprints, ed 1.  J. Bridgland. 11th Triennial Meeting.  Edinburgh, Scotland.  Paris: ICOM. II:692-698.

 

Jansson, P., and R. Shishoo. 1998.  Effect of repeated freezing treatment on the mechanical properties of new wool.  Proceedings of the third Nordic symposium on insect pest control in museums.  Stockholm, Sweden: Naturhistoriska  Rikesmuseet.  57-60.

 

Karel, M. 1985.  Lipid oxidation, secondary reactions, and water activity of foods.  Autoxidation in food and biological systems.  New York: Plenum Press.

 

Michalski, S. 1991.  Paintings: their response to temperature, relative humidity, shock, and vibration.  In: art in transit: studies in the transport of paintings.  ed. M.F. Mecklenburg.  Washington, DC: National Gallery of Art.  223-248.

 

Peacock, E.E. 1999.  A note on the effect of multiple freeze-thaw treatment on natural fiber fabrics.  Studies in Conservation  44(1): 12-18.

 

Pool, M.A., 1997.  Preliminary analysis of the effects of cold storage on fur garments and mammal skins.  Collection Forum  13(1):25-39.

 

Rawlins, J. 2001.  Personal communication.  Section of Invertebrate Zoology, Carnegie Museum of Natural History.  Pittsburgh, PA.

 

Reid, D.S. 1987.  The freezing of food tissues.  In The effects of low temperatures on biological systems.  ed. B.W.W. Grout and G.J. Morris.  London: Edward and Arnold Publishers. 478-487.

 

Roberts, J.D. and M.C. Caserio.  1977.  Basic principles of organic chemistry.  Reading, Massachusetts: W.A. Benjamin Inc. 1270.

 

Taborsky, G. 1979.  Protein alterations at low temperatures: an overview.  In Proteins at low temperatures.  Ed: O. Fennema.  Advances in chemistry series 180.  Washington DC: American Chemical Society: 1-26.

 

Taylor, M.J. 1987.  Physio-chemical principles in low temperature biology.  In The effects of low temperatures on  biological systems.  ed. B.W.W. Grout and G.J. Morris.  London: Edward Arnold Publishers. 17-23.

 

Timar-Balazsy, A. and D. Eastop.  1998.  Chemical principles of textile conservation.  London: Butterworth-Heinemann.  15-25.

 

Toivonen, A.L. 1992.  Investigation of the effects of cold winter conditions on fishing gear materials.  Journal of the Textile Institute 83(1):163-177.

 

Williams, S.L., S.R. Beyer, and S. Kahn.  1995.  Effect of “freezing” treatments on the hydrothermal stability of collagen.  Journal of the American Institute for Conservation.  34:107-112.

 

Wolf, M., J.E. Walker, and J.G. Kapsalis.  1972.  Water vapor sorption hysteresis in dehydrated food.  Journal of Agricultural Food Chemistry 20 (5):1073-1077.  

 

Zachariassen, K.E., 1985. Physiology of cold tolerance in insects.  Physiological Review 64(Oct):799-832.


Integrated Pest Management Made Easy

March 19, 2009

http://www.museums.state.ak.us/documents/bulletin_docs/bulletin_29.pdf

Bulletin No 29, Winter 2007

Your building has pests.  Yes, it really does.  Ours does, too.  But are they a threat to your collection?  With an Integrated Pest Management (IPM) system, you can be active in your prevention of infestation and effective in your response if one occurs.  In the past, museums would respond to evidence of an infestation with poisons.  Many of those substances are now illegal, some contaminated or damaged the artifacts, and most were dangerous to museum staff as well.  Museums took a cue from the agriculture industry, which needed to control bugs on stored grains without contaminating the food with toxins.  An IPM system uses good housekeeping to keep pests out, traps to monitor the presence of bugs, and low temperature to treat infestations.

1. Good housekeeping aims to keep the pests out in the first place.  If you can avoid carrying in new pests, prevent them from entering the building from outdoors, and reduce things that attract them, you’re preventing the problem in the first place.  Here are some of our policies at the Alaska State Museum:
*       Eating is only allowed in the kitchen and conference room.
*       Eating during receptions is kept in a limited area.  The carpet is vacuumed immediately afterwards and trash is disposed of outside the building right after the event.
*       Beverages are not permitted at staff desks with the exception of water, coffee or tea in a closed container.
*       Collections spaces are kept free of non-collections materials and clutter is not allowed.  The cleaner your space, the quicker you will notice something is not right.
*       Packing materials are disposed of in the dumpster outside the building.
*       No plants or flowers are allowed in the building.  None.  They are a proven source of bugs as well as food for the bugs.
*       Structural gaps in the building are closed with silicone caulk, weather stripping or door sweeps.  For rodents, brassy steel wool can plug holes (and doesn’t rust.)  Mice can get through spaces the size of a quarter.
*       ¼” steel hardware cloth is used to cover floor drains.  Rats swim!
*       Keeping water drains on the roof clear eliminates many gnats. Usually a hose works fine.

2. Monitoring your populations with sticky traps gives you an early warning of trouble afoot.  We order our traps through Insects Limited: (317) 896-9300 www.insectslimited.com  The cost is approximately $50 for a box of 100 traps that can be torn into thirds.  That makes 300 traps at about 17 cents each.  For our three floors and approximately 24,000 square feet, we set about 50 traps.  They are also called “blunder” traps, so place them where a bug is likely to stroll in.  This includes along the wall, near sources of water like drains, and next to doorways.  Number each location on a map, and label each trap with its number, location and date.  Change the traps every three months, and keep a chart that describes what you found in each trap.  This task usually takes about 3 hours at the ASM.  If you take a flashlight, checking those dark corners for rodent droppings or other debris is also useful.  Our traps at the Alaska State Museum usually contain lots of spiders and sowbugs (also called pillbugs) as well as ants, large black click beetles, and centipedes.  Google images is helpful, and so are www.bugguide.net and www.museumpests.net.  When we find an insect that looks like a “heritage eater,” but we aren’t sure, we put out extra traps in that location for next time and send the trap to the Forest Service for positive identification.  We also ask staff to catch any bugs they see on a piece of scotch tape.  Anything that was originally a plant or animal has potential for insect infestation.  At the top of the list for tasty bug treats are fur, feathers, leather, and wool.

3. Treatment involves a freezer.  Research indicates that our “heritage eaters” can be killed in all phases of their life cycle by one week below -20°C.  However, many museums only have access to a frost-free freezer, with temperatures that cycle well above -20°C.  Many insects are “frost tolerant” and can make a substance like antifreeze to survive a dose of cold.  But our brains are bigger!  The artifact can be placed in the freezer for a week, then removed and allowed to reach room temperature for 24 hours, and put back in the freezer for another week to deliver a deadly second round of cold.  It is very important to package the artifact properly for low temperature treatment.  You must wrap the artifact in a soft absorbent material such as plain tissue paper, white paper towels, or a soft cloth.  This helps protect it against both the increase in relative humidity at lowered temperature and the slight increase in brittleness when things are cold.  Then, the artifact needs to be placed in a plastic bag that is well sealed.  Squeeze as much air from the bag as you can and seal the Ziplock or use a heat sealer if possible.  Lucky for us, most museum artifacts don’t have enough water in them to create ice.  However, upon removal from the freezer, condensation will form, and it is much better for that moisture to form on the plastic bag than on your artifact!  After a day of adjusting to room temperature, you can safely remove your artifact from the package.  Removing all the old bug debris is a good idea, so any future bug debris will be a clue to a new infestation.  Brushing the debris into the nozzle of a vacuum cleaner with a soft paintbrush usually does the trick.

When infestations occur, not only do the artifacts go into the freezer, but the infested space must be vacuumed, carpet steam-cleaned, and the perimeter of the area dusted with boric acid.  Occasionally, it is necessary to turn to bait.  Ant traps and D-Con are examples of bait, which are not pesticides but kill the pest through mechanisms like thinning the blood to induce internal bleeding.  Bait typically kills much more efficiently than traps.  A recent infestation of picnic ants at the Alaska State Museum was controlled with ant bait that was carried back to the nest.

Many museums do preventive treatment of incoming artifacts with the freezer.  A donation of a fur parka, for example, would definitely go in our freezer before it went into our clean collections room.  What if you don’t have a freezer, or the incoming artifact is too big?  Careful visual inspection in dark crevices can help set your mind at ease.  Look for holes, loose hair, bald patches, live bugs, bug parts, cocoons, webbing, bug nests, and tiny bug droppings known as “frass.”  Frass is round, so suspicious looking dirt can be sprinkled on a piece of paper and the paper tilted…if it rolls easily, it might be frass.  If you don’t see this evidence, the next step is to lay the artifact on a pristine white surface and place some sticky traps around it.  Wait two months or so to allow any eggs to hatch and get active.  If you see no debris on the white surface and nobody in the sticky traps, you’re probably safe.  Preventive treatment is also done with items for sale in the Alaska State Museum gift shop.

An Integrated Pest Management system is part of professional museum practice, just like monitoring your temperature and relative humidity, and keeping your light levels appropriate.  Dealing with an infestation after it happens is upsetting, time consuming, difficult, and often means irreversible damage to museum collections.  An ounce of prevention is truly worth a pound of cure.  Have questions?  Call us!  Scott Carrlee 465-4806 or Ellen Carrlee 465-2396.

Heritage-eating bugs

Common Heritage Eaters
1:00 Cigarette beetle
2:00 Drugstore beetle
3:00 Confused flour beetle
4:00 Saw-toothed grain beetle
5:00 Carpet beetle (black, white, and orange)
6:00 Common carpet beetle larvae
7:00 Varied carpet beetle  (black, white and gray)
8:00 Common dermestid beetle
9:00 Larder beetle
10:00 Webbing clothes moth (ragged wings)
11:00American spider beetle
12:00 Hide beetle (has white tummy)

insect debris

Insect debris from L to R: light brown frass and wood bits from a powder post beetle infestation, #2 pencil, larva and striped shed larval casings, soft white cocoons from the casemaking clothes moth.
Harmless bugs

 
A dime gives scale to these “harmless” bugs as well as the generally smaller-sized “heritage eaters.”

1:00 and 2:00 spiders are very common and may make webs and nests but eat other insects, not collections.  A spider population out of control can be reduced by setting out a large number of sticky traps.
3:00 Minute scavenger beetles eat mostly molds and fungi.  These were living in damp plastic bags used to stuff out a mukluk.
4:00 Common weevil, a grain eater.
5:00 Carpenter ants do not eat artifacts, but if you see one, your building itself could be in trouble.
6:00 Common housefly, mostly a nuisance for leaving droppings called “flyspecks” on artifacts.
7:00 Picnic ants are looking for sugar.  This one was attracted to a puddle of punch spilled under a printer during a reception.
8:00 and 9:00 Sowbugs or pillbugs come in many shapes and are found in damp areas.
10:00, 11:00 and 12:00 Carabids, click beetles and other large beetles are generally harmless and die soon after coming indoors


Dust in Museum Exhibits

March 19, 2009

Bulletin 30, winter 2008  No pdf link on website yet.

We have long known that dust causes damage to artifacts. The basic
information we tell museums about dust includes:

1.      Dust is unsightly and makes your collection look poorly
maintained.
2.      Dust is abrasive on a microscopic scale due to tiny sharp
mineral particles, such as quartz.
3.      Dust contains pollens, skin cells, insect bits, and other
organic matter that feeds biological growth.
4.       Dust can be acidic.
5.       Dust is “hygroscopic,” meaning it attracts water and holds it
against the surface of an object, contributing to staining, corrosion,
and biological growth.

Recent articles have given us a new understanding of the impact of dust
on our collections.  A paper presented at the 2004 conference of the
American Institute for Conservation  described the forces that help dust
stick to surfaces.  One of these forces comes from sticky “exopolymers”
made as a waste product of microbes (mainly bacteria).  Accumulating
dust provides more food for these colonies of microbes, and layer upon
layer of “biofilm” forms, with the bottom layers becoming firmly adhered
to the surface of your artifact.  Spikes in humidity can encourage the
initial growth and speed the growth of biofilms.  Periods of low
humidity after high ones can stress the bacteria, and might cause them
to produce even more sticky exopolymers.  Yet another reason to try to
keep our museum humidity levels stable!

Other recent articles have explored the role of visitors in creating
coarse dust.  Considerable amounts of dust enter the museum on visitors’
clothes and shoes. Visitors are such a direct contributor to dust that
one study showed dust amounts are cut in half for every 3 to 4 feet of
distance between a visitor and an object. Fibrous dust, largely from
clothing, accounts for only about 3% of the dust in exhibits. But since
the particle size is large and visible, fibrous dust contributes
significantly to the appearance of dustiness. This dust tends to be
thickest at eye level. Dust entering on shoes is more concentrated
closer to the entry, and in greater quantity under wet weather
conditions than dry conditions. This kind of dust only rises about 4 or
5 inches off the floor.

Some preventive measures can be taken. Placing objects in cases and
further away from visitor traffic is one solution, of course, but is not
always possible or desirable. Tightly sealed exhibit cases are better
than ones with gaps, but require construction materials that do not
off-gas harmful chemicals like formaldehyde and acid.  Placement of mats
in entryways significantly reduces the amount of dirt brought into the
building on shoes. Vigorous air movement also increases the rate of dust
coverage. Live performances and pathways through exhibits that involve
sharp turns are examples of “dust raising” activities. Air movement from
fans and open windows encourages dust circulation as well. Sometimes
those factors are unavoidable, but strategic decisions can be made,
particularly in relation to artifacts on open display.

Cleaning of collections on exhibit should be scheduled at least once a
year. Objects displayed in the open should be dusted annually. Artifacts
in exhibit cases can be cleaned on a rotating schedule, with a few
exhibit cases cleaned one year and others the next. After a few years,
all cases will be done and the rotation can begin again. It is useful to
have a map of exhibit galleries that can be annotated with notes and
condition reports if needed.

Good housekeeping is divided into two levels of cleaning. Regular
less-skilled cleaning can be done by janitorial staff or untrained
volunteers, including daily vacuuming and regular dusting of furniture.
Specialized cleaning of exhibits requires more skill. HEPA-filtered
vacuums are especially helpful, since they release less dust back into
the air than traditional vacuum cleaners. Closer to collections objects,
vacuums with adjustable suction (such as a Nilfisk vacuum with a
rheostat) are preferable. Dusting techniques that involve rubbing are
abrasive to most surfaces on a microscopic level, and are best avoided
if possible. Most items can be effectively cleaned with a soft
paintbrush, gently fluffing the dust from the surface into the nozzle of
a vacuum cleaner. For fragile surfaces, you may cover the nozzle with
fine nylon netting, such as tulle, secured with a rubber band.  Many a
loose bead or detached fragment has been saved this way, and you will
see sooner if the suction is too strong (hairs pulled from a taxidermy
specimen, for example).  Feather dusters can be helpful, but beware of
any rough quills that could scratch surfaces and be sure to vacuum the
feathers frequently to remove dust.

Glass and plexiglass surfaces are often the first to show dust. The
Sheldon Jackson Museum in Sitka, which has some of the cleanest exhibit
galleries in the state, has found that cleaning glass with paper towels
and a mixture of 1 part white vinegar to 4 parts water is as effective
as any cleaner. Any cleaner should first by applied to a cloth, and then
to the glass or plexi. Fine mist spray can penetrate cracks of exhibit
cases and damage artifacts. Always be careful to let the case air out
before closing because of the acetic acid or ammonia vapors released by
some cleaners.

Plexiglas(r) requires special attention to prevent the plastic from
fogging or scratching. The Alaska State Museum uses specially formulated
commercial Plexiglas(r) cleaners. One product is called Norvus, and is
available on the Internet through vendors such as Amazon.com and Tap
Plastics.  Novus 1 is for cleaning, Novus 2 is for removing fine
scratches, and Novus 3 removes heavy scratches. Apply with a clean
cotton rag.

Good housekeeping is an important part of preventive conservation.
Cleaning also gives you an opportunity to inspect your exhibits for
problems such as bugs or shifted objects. While updating exhibits is
often not in the budget, dusting costs little and freshens up
appearances.

(sidebar)

Five Defenses Against Dusty Exhibits
1. Sealed exhibit cases are the gold standard.
2. Establish regular dusting schedules.
3. Use extra floor mats near doors.
4. Avoid the use of fans and open doors or windows unless absolutely
necessary.
5. Avoid drastic swings in humidity levels.
6.  Shut down the HVAC when cleaning dust out of the vents.

References:

Tarnowski, Amber L., Christopher J. McNamara, Kristen A. Bearce, and
Ralph Mitchell.  “Sticky Microbes and Dust on Objects in Historic
Houses.”  AIC Objects Specialty Group Postprints, Vol. 11, 2004.
 Yoon, Young Hun and Peter Brimblecomb.  “Dust at Febrigg Hall.” The
National Trust View, Issue 32, Summer 2000.


New Frontiers for the Conservation Lab

March 19, 2009

http://www.museums.state.ak.us/documents/bulletin_docs/bulletin_26.pdf

Bulletin 26 Spring 2007

Published as “Conservator’s Corner”

by Ellen Carrlee

 

Along with other renovations in the Alaska State Museum basement, the
conservation lab has had a makeover, with new flooring, new paint, and
new lab tables.  The spruced-up space will be used for treatments, the
conservation library, the conservator’s office area, textile
conservation supplies, study samples (fragments of ivory, skin, basketry
and other materials for developing treatments) and the binocular
microscope.  The new tables for treatments have chemical-resistant black
resin tops and are the kind typically used in college chemistry
classrooms.  The narrow former darkroom that served as the only
conservation lab space for many years can now be used more effectively
as the conservation chemical laboratory, with its deep sinks, fume hood,
and safety features such as a flammables storage cabinet and emergency
eyewash station.  Most conservation treatment supplies are stored there,
and certain wet treatments will still occur in that space.  First on the
docket will be a basketry conservation project to finish the treatment
of several waterlogged archaeological baskets from southeast Alaska.
Among the most important are two very old baskets that have already
received impregnation with polyethylene glycol (PEG) wax to replace the
excess water.  Water has such strong surface tension that simple
evaporation from old waterlogged wood and basketry materials causes
warping and severe damage.  While the PEG treatment was successful in
halting deterioration, these ancient baskets are still too fragile to be
exhibited.  A consolidation is needed, and research is underway to
determine the best approach.  Two graduate students in conservation will
be coming to assist in this project as well as treat other baskets in
the ASM and SJM collections.  Molly Gleeson will be coming from the
UCLA/Getty Museum art conservation program, and Samantha Springer will
be coming from the Winterthur/University of Delaware art conservation
program.  They will arrive in mid-June, spending several weeks in Juneau
working on the collection and learning about gathering and processing
spruce root and an introduction to weaving from Tlingit/Haida weaver
Janice Criswell.  Then they will travel to Sitka to work on the Sheldon
Jackson Museum collection and learn more about weaving from Tlingit
weaver Teri Rofkar until mid-August.  The interns will also share their
knowledge and treatment techniques with the weavers in what promises to
be an exciting and rewarding collaboration.  Successful treatments will
mean many important historical and archaeological baskets currently too
fragile to be exhibited will be able to be studied, appreciated, and
enjoyed by the public.

 

Conservation Lab BEFORE

Conservation Lab BEFORE

 

Conservation Lab AFTER

Conservation Lab AFTER


2007 Basketry Internship

March 19, 2009

http://www.museums.state.ak.us/documents/bulletin_docs/bulletin_27.pdf

Bulletin Vol 27 Fall 2007

The Alaska State Museum conservation lab hosted two interns for a basketry conservation project this summer.  Both interns were graduate conservation students finishing their second year of studies: Molly Gleeson from the UCLA/Getty Museum program, and Samantha (Sam) Springer from the University of Delaware/Winterthur Museum program.  These programs and the interns themselves provided the funding to come to Alaska.  The ASM provided the supplies and supervision.  In the first week, Molly and Sam brainstormed treatment solutions for the archaeological basketry fragments in the lab, and did a preliminary cleaning on a group of flattened spruce root work baskets that may become a study collection.  In the second week, curator Steve Henrikson assigned each intern two horrifically damaged baskets.  Molly worked on two Haida baskets collected by Lt. George Thornton Emmons in the late 1800′s.  The baskets had severe deformation, losses, tears, and old repairs of painted tape.  Sam’s Tlingit basketry projects also had intense tears, losses and deformation as well as old insect infestation and surface soiling.  The two Tlingit baskets still retain the inverted Y-shaped folds on the sides that indicate the baskets were folded for storage and thus not made for the tourist market.  Treatments included overall re-shaping in a humidity chamber, localized humidification with Gore-tex and blotter paper to align tears for repair with tiny splints of Japanese tissue and wheat starch paste, and innovative loss compensation with cotton gauze and sculpted paper pulp bulked with adhesive.  The interns were also able to examine baskets in the collection with Steve Henrikson and Tlingit-Haida weaver Janice Criswell.  Janice and weaver Mary Lou King twice took the interns “rooting.” They dug spruce roots, processed them, and each wove a basket under the tutelage of Janice and Mary Lou.  Together the interns formed quite a dynamic duo, becoming fast friends and helping Ellen make improvements to the lab.  Molly’s boyfriend Germán visited from Chile and proposed marriage on a beautiful Eaglecrest hike.  Germán and Samantha’s husband Seth also became friends, hiking and seeking satellite TV soccer matches while their partners immersed themselves in basketry.  Samantha’s professor Bruno Pouliot from Delaware also visited the interns for several days, and accompanied them to Sitka to kick off the second part of their internship.  Their first day on the job, they appeared on the radio to promote that evening’s free public program at the Sheldon Jackson Museum, a Conservation Clinic to provide advice to locals about their artifacts.  The clinic included ASM Curator of Museum Services Scott Carrlee (also a conservator.)  More than fifty people came, most bringing artifacts for examination, making the event one of the most successful public programs at the SJM in recent years.  In addition to several basketry treatments, the interns were able to meet with retired curator Peter Corey, National Parks Service curator Sue Thorsen, and Tlingit weaver Teri Rofkar to study baskets.  They also gathered materials and wove baskets with Teri.  In an exciting development, the interns are working with Teri and Janice to co-author a paper for an important international museum conference.  The International Council for Museums Conservation Committee (ICOM-CC) holds a major conference every three years.  In 2008, the conference will take place in New Delhi, India with the theme “Diversity in Heritage Conservation: Tradition, Innovation and Participation.”  The basketry abstract was provisionally accepted in July.  Only 40% of the proposed abstracts were accepted, and final paper is due in November for final review.  If accepted, this will be one of the very few professional conservation papers that will include a first-person Native voice, instead of the Native perspective only interpreted through a conservator.  Internships such as this one provide up-and-coming conservation professionals an opportunity to work with Native artists and museum professionals in the environment where the artifacts were made, allowing for multiple perspectives and a deeper understanding of the conservator’s sensitive role in preservation.  These are lessons that can be carried on throughout their careers.  In return, interns take on difficult treatments and share the latest techniques and theories in conservation they have learned in school.  Today’s interns are tomorrow’s professionals, linking us to museums in the lower 48 and creating a network of colleagues.  The long-range plan for the ASM conservation program includes dividing the collection into materials groupings for systematic surveys.  Each survey will identify priorities for conservation treatment and provide ideal internships for future conservation students.  Next summer’s project targets the museum’s natural history collection.  Stay tuned…

Rim of spruce root basket 2006-18-1 BT by Samantha Springer

Rim of spruce root basket 2006-18-1 BT by Samantha Springer

 

 After treatment by Samantha Springer using Japanese tissue and paper pulp with wheat starch paste and watercolor.

After treatment by Samantha Springer using Japanese tissue and paper pulp with wheat starch paste and watercolor.

 

 

 

 

 

 

Molly Gleeson inventing a new repair technique using cotton gauze, paper pulp, Japanese tissue, wheat starch paste and PVA emulsion adhesive.

Molly Gleeson inventing a new repair technique using cotton gauze, paper pulp, Japanese tissue, wheat starch paste and PVA emulsion adhesive.

After treatment of large loss near base of Haida basket II-B-493

After treatment of large loss near base of Haida basket II-B-493

 

Janice Criswell teaches Samantha Springer to weave spruce root in Mary Lou King's kitchen.

Janice Criswell teaches Samantha Springer to weave spruce root in Mary Lou King's kitchen.


Conservation and Exhibit of an Archaeological Fish Trap

March 19, 2009

AIC Objects Specialty Group Postprints, Volume 13, 2006

Abstract
In 1991, salvage archaeology rescued a 500-700 year old basketry fish trap in Juneau, Alaska. Preliminary treatment with polyethylene glycol (PEG) was done to prevent the collapse of the waterlogged wood, and the trap was held in conformation with an elaborate system of foam, mesh, Plexiglas, and slings that made study or exhibit impossible. The fragile spruce root lashings remained wrapped from salvage. The challenge was how to treat and exhibit an artifact that could not be set down on a flat surface, as it could not support its own weight. The conservator and mount maker worked as a team, each stabilizing areas to allow the other access. The materials used were Japanese tissue with a combination of wheat starch paste and PVA emulsion, bands of Tyvek attached with B-72 to secure lashings, and a three-part approach for overall support with Plexiglas, Mylar slings, and brass mounts.

1. Discovery
In 1989, Paul Kissner (retired from the Alaska Department of Fish and Game) was fishing in Montana Creek near its confluence with the Mendenhall River when he saw the top of an artifact eroding from the riverbank. He contacted Professor of Anthropology Wallace Olson (University of Alaska Southeast) and curator Steve Henrikson (Alaska State Museum) who removed the exposed section of what turned out to be a fish trap as an emergency measure to prevent its loss through erosion. Wallace Olson describes the discovery,

“When the remains of the Montana Creek fish trap were first discovered, I was called and went to the site. What I saw was portions of something that appeared to be a fish weir or trap, protruding out of the silt in the creek. It was drying and falling apart as it was exposed to the air and sun. I immediately went to a local hardware store and bought every plastic “tie” they had in stock. I secured the pieces as best I could in their original position. The next day, Steve Henrikson, of the Alaska State Museum, came out and helped secure the remains. All we knew was that it was the top part of a traditional fish trap. As we finished salvaging the remains, Steve saw, and realized that it was an entire fish trap, and that what we had saved was only the top half. It was a monumental archaeological find on the Northwest Coast” (Olson 2005).

Ownership of the trap was complicated from the beginning. The area where the trap was found is the traditional fishing territory of the Auk Kwaan of the Tlingit people. (A kwaan is a region controlled by several clans.) Genealogical reckoning indicates these people arrived from the Stikine River area near modern Wrangell several hundred years ago. Montana Creek is a freshwater river, but also influenced by tidal action. It was therefore somewhat unclear if the location was today the property of the City of Juneau, or the State of Alaska. Non-navigable freshwater rivers are the jurisdiction of the City, while navigable freshwater rivers and intertidal areas are the jurisdiction of the state. At the time of excavation, the City formally declined ownership, although the waterway has some tidal influence and is only navigable by a canoe or kayak. The Alaska State Museum (ASM) has not accessioned the trap into its permanent collection, and local Native groups including the Sealaska Corporation, Tlingit-Haida Central Council, and the Auk Kwaan continue to take an active interest in the trap.

The trap was originally cylindrical in form with straight sides and an interior funnel lashed to the front end. The trap was crushed in burial. Materials were identified as spruce (Picea sitchensis) by Mary Lou Florian of the Royal British Columbia Museum (Florian 1992) and hemlock (Tsuga heterophylla) by Bruce Hoadley (Hoadley 2005). For descriptive purposes, the trap remains may be divided into five sections: the entrance funnel, the main body, the detached “top” body fragment, and the deformed tail. The funnel is now a lenticular flattened oval. Long, straight pieces of hemlock (referred to as “staves” in the excavation report) intersect hoops of spruce branch where they are lashed together by spruce root. This root is wrapped around the hoop continuously until the intersection with the stave, where it loops around, forms a double or triple “X” with a cinch loop to keep it tight, then continues to wrap around the hoop to the next intersection. Overhand wrapping holds the funnel, which was constructed separately, within the body of the trap. The main body includes a section of shorter staves with tool-worked ends and fragments of cordage that suggest a possible door on a rope hinge. The far back end of the trap does not survive, but measurements of the hoops indicate that the trap did not taper. The tail of the trap includes only 18 staves of the full cylinder (40 staves total) and is bent upwards at an angle of approximately 45 degrees.

2. Excavation
Salvage archaeology began in 1991 (permit 49-JUN-453,) mainly undertaken by excavator Jon Loring, geomorphologist Greg Chaney, and archaeologist Robert Betts. The permit was issued for a time period when fish activity in the river was low, unfortunately corresponding to the rainy cold weather of fall and winter, and excavation took place between tides with sandbags and pumps to fight the water. The trap was taken by skiff and then truck to the Alaska State Museum (ASM) where it was treated with mixed low and high molecular weight polyethylene glycol (PEG) for approximately one year. The treatment was done by Jon Loring, who had some direction from the staff at the Canadian Conservation Institute and ASM conservator Helen Alten. The major funding for the excavation of the trap came from Sealaska Corporation, the Southeast Alaska Regional Native Corporation owned and run by Tlingit, Haida, and Tsimshian shareholders and formed as a result of the 1971 Alaska Native Claims Settlement Act. Since ownership of the trap was unclear, most of the excavation documentation was kept by Jon Loring (Loring, 1995.) This is the first basketry-style fish trap known to be recovered from an archaeological context on the Northwest Coast. Traps were usually removed from the streams after the runs of fish ended each year. They were stored near the fishing site or returned to camp for repair (Henrikson, 2005.) According to the excavators, high iron content in the soil along with quick burial of the trap by an advancing river bar and tidal action are thought to have contributed to the survival of this trap. Interviews with Tlingit elders about fish traps were conducted in 1992 and included in the excavation report (Loring 1995.) Radiocarbon dating of fragments from the 1989 discovery sent to Washington State University indicated the trap is approximately 500 to 700 years old. Sample 1 (WSU-4140) gave a result of 500 +/-70 and Sample 2 (WSU-4141) gave a result of 700 +/- 60 using the computer calibration program developed by geoscientist Minze Stuiver of the University of Washington and run by anthropologist Jon Erlandson from the University of Oregon (Erlandson 1990.) In 2004, the Juneau-Douglas City Museum (JDCM) was awarded a grant from the Alaska State Museum Grant-in-Aid program to conserve, mount, and exhibit the fish trap.

3. Condition when excavated and initial treatment
Approximately 80% of the trap still exists. The trap was crushed in burial and the back end of the trap did not survive, resulting in a mystery about how the trap terminates at that end. The top section is separate from the larger bottom section, and there are perhaps 10 staves missing. Most of the spruce root lashing on the top section of the trap did not survive, but perhaps 60-70% of the lashing on the main section was still present during excavation. The funnel end is quite well-preserved, although crushed into a lentoid shape with pointed corners at each side of the trap. The back end of the trap was found bent upwards with staves broken, yet still connected to the main section by a badly distorted spruce root branch hoop.

The top section of the trap exposed by erosion was removed first. Most of its spruce root lashing was lost in burial and/or erosion from the river bank and the plastic “zip ties” used to hold the elements together for transport and salvage caused some additional damage from abrasion. (“Zip ties” are plastic strips available from the hardware store with a self-ratcheting action that allows them to be pulled tighter but not looser.) Storage in a fresh water tank before treatment flattened this section somewhat, although it appears that attempts were made to correct this curvature during subsequent treatment. The bottom section was more carefully supported during excavation with a frame of aluminum conduit (custom shaped in the field with a pipe bender), 1″ nylon webbing straps, 3″ plastic mesh straps, and polyethylene foam inserts to form a hammock and help maintain its shape during transport and treatment at the Alaska State Museum.
During excavation, the fragile spruce root lashings were covered with cotton gauze in the roll form typically used for bandages. Areas that were particularly deteriorated were not wrapped with the gauze but encapsulated in fine polyester netting with loose stitches of white cotton thread. One area on the main section where twined cordage survived was wrapped in roller gauze and then sandwiched between large stiff pieces of plastic mesh that were stitched together to give the area rigidity. In the field, the funnel of the trap was supported with individual balloons inflated to give needed support. These were later replaced with blue polyethylene foam inserts carved to shape. Following treatment of the two main sections in PEG, the trap was allowed to slowly air dry on the support frame and put into storage. This hammock/frame unit was suspended from a wooden exterior to hang free like a baby cradle (Fig. 1).

fig11

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Fish trap in storage supports from initial treatment. Funnel at bottom and cylindrical main body are flattened, and the distorted tail section is visible at the top of the image.

Additional pieces of polyethylene foam were inserted to hold the interior curvature of the trap with the aid of adjustable Plexiglas rectangles or “fingers” to follow the contour. These pieces of Plexiglas were individually adjusted (like a feeler gauge) and screwed firmly between a sandwich of narrow plywood boards. The ends of these plywood boards were lashed to the conduit with yellow nylon cord. (Medex, a medium density fiberboard bonded with polyurea-isocyanate resin, was originally used instead of Plexiglas, but it reportedly grew thick fuzzy mold quickly and was replaced as per Loring 2005.) The cotton roller gauze was left covering the lashing throughout the PEG treatment and subsequent storage. While many additional detached fragments were treated, some were not treated but left wet and kept in plastic bags. Most of the notes from the field excavation and treatment could not be found in 2005, but the excavation report and many slides were available and Jon Loring (also on the mount making team for the 2005 project) was able to recount much of what happened (Loring 2005.) A label on the lid of the box where some cordage was stored reads: “PEG 20% u/v Reg 200 Start 6-9-97 12-11 to 26 Drying.” The 1992 site overview plans indicated the proposed treatment as “25% solution of 10% PEG-200, 5% PEG-1000 and 10% Compound 20M in 500 gallons of water.”

4. Condition and treatment before exhibition
Examination in 2005 indicated the PEG treatment worked well. The wood was a slightly darkened reddish or yellowish brown color from the paler excavation color (Loring 2005,) but still had the feel and look of wood, and the weight also seemed normal, if slightly lighter than expected. The wood seemed stable and reasonably sturdy, although there were breaks through several staves. It is unclear if these breaks happened during excavation or subsequent treatment, but most do not contain sand or debris at the splintered break edges. These areas might also have been weakened in burial. Unwrapping a small test area indicated the roller gauze did not stick to the trap, but the spruce root lashings were very fragile, brittle, broken in many places, and were no longer providing any structural stability to the trap. There was significant dirt, sand, and small rocks between the lashings as well.

It was not possible to know exactly how difficult the treatment would be until work began. It was necessary to stabilize the spruce root lashing, stabilize the junctures, and make supportive mounts simultaneously, as each process facilitated access to the others. Working together, the conservator would stabilize the lashings enough to allow mount makers to support the trap and remove pieces of the cumbersome old support system, which in turn allowed the conservator access to additional areas to treat. Since the trap is basically a large cylindrical grid of staves and hoops attached at their junctures, maintaining attachment at these junctures was essential to the stability of the trap. The condition of the lashings did not allow them to perform this function. A combination of reinforcements for these individual points of connection, together with an externally supportive mount structure, would hold the trap in place without stressing the fragile lashings (Fig. 2).

fig2

 

 

 

 

 

 

 

 

 

Figure 2. Spring 2005 treatment in the lobby of the Alaska State Museum, with exhibit designer Robert Banghart (left) working on Mylar slings for the body of the trap. Dark strips below the body of the trap are plastic mesh and nylon webbing supports from the excavation. Ellen Carrlee (right) works on treatment of the lashings from the detached top section.

The support strategy utilized five main materials: Japanese Kozo paper, Tyvek (spun bonded polyolefin fiber in sheet form grade 1020 smooth texture), Mylar (polyester film), Plexiglas acrylic sheet, and brass. The Japanese paper was used to stabilize the lashings, whose condition could not be assessed until the unwrapping began. Luckily, the gauze wrapping did not stick to the spruce root lashings as a result of the PEG treatment, although splinters and dirt caused some snagging between the cotton and the artifact (Figs. 3-4).

fig3

 

 

 

 

 

 

 

 

 

Figure 3. Corner of funnel before treatment, with cotton gauze wrapping from excavation covering spruce root lashings.

fig4

 

 

 

 

 

 

 

 

 

Figure 4. Corner of funnel during treatment, with spruce root lashings partially exposed, Japanese tissue repairs tucked under loose lashing fragments.

In each area, the top surface of the gauze wrapping would be cut open with a small scissors, partially peeled back and the surface cleaned with puffs of air and a soft paintbrush until the loose lashing pieces indicated mobility. Small torn pieces of Japanese paper approximately 1 cm square were saturated with a wheat starch paste/PVA emulsion mixture and tucked into the interstices of the lashing wherever possible with a pointed tweezers. Saturated pieces of tissue could also be folded to serve as a gap-filler and adhesive for small detached fragments of the lashing. Points of good contact between the lashings and the hoops were sporadic, making a gap-filling measure necessary. The weakest adhesive possible was sought to ensure that any stress would cause the repair to fail instead of causing new damage to the artifact. Wheat starch paste alone was insufficient to support the weight of the fragments challenged by gravity. Methylcellulose was too weak as well, and not surprisingly, the two in combination were also too weak. The adhesive selected was wheat starch paste with a few drops of Jade 403 polyvinyl acetate (PVA) emulsion added to each batch. A batch size was the amount that conveniently fit into a large watch glass. Pieces of Japanese paper could be dragged through the adhesive and kept at the edge of the glass for application. Allowing them to dry slightly made them more tacky. These repairs reached full strength overnight, and the next day the underside of each lashing section could be unwrapped. More loss occurred as wrapping was removed since gravity pulled the exposed lashing fragments from the undersides of the hoops. To combat this problem, adhesive-soaked Japanese paper was tucked in before the fragments could fall. Cleaning these areas was not possible, and significant sand and dirt was consolidated into the paper. In some areas, there was no lashing under the gauze. In other areas, the lashings were badly crushed and could not be saved, or only partially saved. Approximately 30-40% of the main section of the trap had lashings that could be preserved to a degree that the wrapping technique could be studied. The Japanese paper could be tucked away out of view in many cases, but in others had the appearance of small white spitballs. The visibility of these was reduced by dotting acrylic emulsion paint on them with a tiny paintbrush to mimic the surround.

The trap was stabilized at junctures between the hoops and staves by narrow strips of Tyvek painted with acrylic paint in a brown, striated pattern on the top side only. One end of the Tyvek strip was attached underneath the juncture to either the hoop or the stave with Acryloid B-72 and allowed to dry. The strip was then pulled diagonally over the juncture to form a loop, snugged gently, and adhered to itself over the same area it was attached to the wood. Whenever possible, the Tyvek was slipped under the original lashing to help hide the Tyvek. Tyvek was chosen because it was lightweight, flexible, strong, and inert. All Tyvek strips were cut approximately the same width and painted a uniform color with acrylic emulsion paint (slightly distinct from the lashing color.) These strips were attached in the same diagonal direction as each other with the intent to have these stabilizing elements fully visible but camouflaged. They form a pattern with their regularity and can thus be easily distinguished from the real lashings by viewers studying the construction technique (Fig. 5). 

fig-5

 

 

 

 

 

 

 

 

 

Figure 5. Corner of funnel during treatment, with Tyvek strips attached. Tyvek gives physical support no longer provided by the original lashings. The Tyvek is painted a uniform color sdistinct from the spruce root color to allow the viewer to distinguish repairs from the original lashing.

Determined viewers can also peek up from below and catch a glimpse of the unpainted white undersides of the Tyvek strips.  Mount making was designed and supervised by Robert Banghart of Banghart and Associates. The primary support for the main body of the trap was made from three 6″ wide clear 10 mil Mylar straps used as a cradle (Fig. 6).

fig6

 

 

 

 

 

 

 

 

 

Figure 6. Mylar slings hang below the trap in preparation to replace the darker plastic mesh and nylon webbing straps supporting the underside of the trap. Mylar is temporarily clamped onto the uptake spool of metal supports made from basic plumbing supplies.

Mylar was chosen because of its flexibility and strength. It was feared that flaws might cause the Mylar to split and quickly propagate a tear (stress razor) but testing of the material with heavy weights and punctures indicated the material would not fail in this manner. The Mylar slings were held with supports made from standard plumbing supplies. The end of each Mylar sling was rolled onto an uptake spool made from a tube of ½” rigid copper with mild steel reinforcement rod attached on the interior of the tube with Scotch-Weld epoxy adhesive. The tube could be rolled like an axle where it entered a right-angle elbow-shaped street 90° pipe and held with a stainless steel set screw (hex drive with a national fine thread pitch of 8/32.) The right angle pipes were connected to legs of steel-reinforced copper tube by a silver solder join, and set in a steel floor flange that was screwed to the deck. Strong gaffer’s tape was initially used to hold the end of the Mylar to the uptake spool, but over time, the tape was not sufficient due to lack of compression strength on the uptake spool. To remedy the problem, clips were made from ¾” acrylonitrile butadiene styrene (ABS) plastic with a slot cut to create a “C” shape. In the future, use of these clips directly on the uptake spool to hold the end of the Mylar would be preferred. Curved sections of Plexiglas were added at the front and under the tail to prevent shifting of the trap. Additional 1/8″ extruded Plexiglas rod stops were added to the tail support to prevent shifting of the slanted tail area. Extruded Plexiglas rod was used where possible to support the Plexiglas, with a brass pin holding the Plexiglas and rod together. Loctite cyanoacrylate adhesive with accelerant was used to adhere the pin and the rod. Padded brass mounts rising from the deck were added at various locations to provide individual support to detached or broken areas. Polyethylene felt with acrylic adhesive backing was used for padding. More than 30 detached pieces from the trap ranging in size from 10″ to 55″ were not reattached and exhibited with the trap. Most of these pieces were not attached to the trap when excavated and their exact placement cannot be determined easily because break edges were deteriorated. Some pieces whose locations were known were not reattached. Each piece would have required its own padded mount and the inner, empty cavity of the trap would then be filled with a forest of mounts, making the shape of the trap difficult for the viewer to read. The measurements of these pieces, however, helped confirm the original size of the trap. Janice Criswell (Tlingit-Haida basket maker and instructor, University of Alaska Southeast) and her husband Steve Henrikson (Curator of Collections, Alaska State Museum) were commissioned to construct a full-scale replica of the trap. The replica was completed in March of 2006 and suspended above the original artifact to help the viewer understand the archaeological remains (Fig. 7).

fig7

 

 

 

 

 

 

 

 

 

Figure 7. Montana Creek Fish Trap with repairs complete, undergoing final mount fittings. View looks into funnel of trap, with detached top section supported above the main body and bare sticks of distorted tail projecting upwards at the far end of the trap.
A 4 ½” thick box truss was attached to the underside of the plywood that formed the original base of the trap support system. The surface of the plywood was covered with three coats of latex acrylic paint. The deck was covered with well-washed gray river rock to cover the mounting hardware and mimic the river bed where the trap was found. The trap does not touch the deck or the rocks.

Wallace Olson described the finished exhibit:
“As an anthropologist and archaeologist, I was happy that at least we were able to salvage some remains. I never expected, or hoped that the entire trap would be preserved…I was convinced that there was no way that a six-hundred year old fish trap, partially exposed to the air, crushed in its burial, could ever be displayed or replicated. My hope was that at least we might save a few pieces and carbon-date them. In spite of my doubts, the staff at the Juneau-Douglas City Museum was able to design and build a beautiful non-obtrusive support system to display the trap. When one looks at the display model, it is exactly the same as what I, and the archaeologists found. Today, as someone who was “on the scene,” from the beginning, I can walk into the Juneau-Douglas City Museum and honestly tell people, “Yes, that’s the way it was found and recovered” (Olson 2005).

figure-8

 

 

 

 

 

 

 

 

 

 

 

 

Figure 8 Trap in exhibit case with replica by Janice Criswell and Steve Henrikson suspended above. The archaeological trap remains are crushed but the replica suggests its original shape.

Supplies
ABS plastic pipe, set screws, steel floor flange, street 90° pipe,
Plumbing supply stores or local hardware stores.
Acryloid-B72® ethyl methacrylate (70%) methyl acrylate (30) co-polymer in acetone and ethanol:
Conservation Resources International LLC. (www.conservationresources.com)
Jade 403 polyvinyl acetate emulsion, Kozo Japanese paper, Tyvek spun-bonded polyolefin fabric in grade 1020 smooth texture:
TALAS (www.talasonline.com)
Liquitex acrylic paint in burnt umber, red oxide, and yellow oxide:
Art supply stores such as Dick Blick (www.dickblick.com).
Loctite cyanoacrylate adhesive with accelerant, Maylar polyester film (10 mil), Scotch-Weld DP-100 Quick Set Epoxy:
McMaster Carr (www.mcmaster.com).
Padding of polyethylene felt with acrylic adhesive backing:
Benchmark (www.benchmarkcatalog.com).
Permacel Professional Grade Gaffer’s Tape:
Theater or sound equipment supply stores, or at Uline (www.uline.com).
Wheat Starch Paste. Commercially available product made in Japan, from the supply at the Alaska State Museum conservation laboratory. Label in Japanese. Comparable product sold at TALAS as Zen Shofu Wheat Starch Paste (www.talasonline.com).

References
Banghart, Robert. 2005. Personal communication. Principal of Banghart and Associates Exhibit Design. Douglas, Alaska.
Erlandson, Jon. 1990. Personal communication. Professor of Anthropology, University of Oregon. Eugene, Oregon.
Florian, Mary-Lou. 1992. Personal communication. Conservation Scientist, Royal British Columbia Museum. Victoria, British Columbia, Canada.
Henrikson, S. 2005. Personal communication. Curator of Collections, Alaska State Museum, Juneau, Alaska.
Hoadley, R.B. 2005. Personal communication. Professor of Building Materials and Wood Technology in the Department of Natural Resources Conservation at the University of Massachusetts Amherst.
Loring, J. 2005. Personal communication. Excavator, mount maker. Juneau, Alaska.
Loring, J. 1995. The Excavation of Basket-Style Traps. Montana Creek Fish Trap Site, Juneau Alaska (49-JUN-453). Unpublished typescript. Juneau-Douglas City Museum, Juneau, Alaska.
Olson, W. 2005. Personal communication. Emeritus Professor of Anthropology, University of Alaska Southeast. Juneau, Alaska.
Additional Sources
Betts, R.C. 1998. The Montana Creek Fish Trap I: Archaeological Investigations in Southeast Alaska. In Hidden Dimensions: The Cultural Significance of Wetland Archaeology. Ed. Kathryn Bernick. University of British Columbia Press. Victoria, British Columbia, Canada.
Betts, R.C. 1992. Northwest Coast Basket-Style Fish Traps: Ethnographic and Archaeological Background. Paper presented at the 19th Annual Alaska Anthropological Association Meeting. Fairbanks, Alaska.
Campbell, C.R. 1994. An Archaeological Survey of the West Mendenhall River Tail. State of Alaska Department of Transportation Project No. 71466. C.R.C. Cultural Resources Consultant. Unpublished typescript. Ketchikan, Alaska.
Chaney, G. n.d. Montana Creek Fish Trap Stratigraphy Interpretation. Unpublished typescript. Juneau-Douglas City Museum, Juneau, Alaska.
Chaney, G. 1998. The Montana Creek Fish Trap II: Stratigraphic Interpretation in the Context of Southeast Alaska Geomorphology. In Hidden Dimensions: The Cultural Significance of Wetland Archaeology. Ed. Kathryn Bernick. University of British Columbia Press. Victoria, British Columbia, Canada.
Criswell, J. 2005. Personal communication. Tlingit-Haida basket-making instructor. University of Alaska Southeast, Juneau, Alaska.
Miller, K. 2005. Personal communication. Anthropologist, Sealaska Heritage Foundation. Juneau, Alaska.
Emmons, G. T. 1991. The Tlingit Indians, ed. F. DeLaguna. Seattle and London: University of Washington Press. New York: American Museum of Natural History.
Stewart, H. 1994. Indian Fishing: Early Methods on the Northwest Coast. Seattle, Washington: University of Washington Press.


Does Low-Temperature Pest Management Cause Damage?

March 19, 2009

http://cool.conservation-us.org/coolaic/jaic/articles/jaic42-02-002_indx.html

ABSTRACT—Preventive low-temperature treatment as a means of pest control during the relocation of the ethnographic collections of the National Museum of the American Indian afforded the opportunity to undertake an observational study of potential damage from this treatment. Does low temperature harm materials thought to be vulnerable? What are the possible causes of damage from this treatment? The study revealed no visible damage to any of the materials treated, although the literature suggests that minor changes on a molecular level are likely. The literature also indicates that the effects of changing relative humidity and water relationships are less of a threat than effects related to low temperature alone, such as shrinkage, embrittlement, and molecular alteration. The first part of the article discusses the threat (real or imagined) of various damage mechanisms, and the second part addresses several categories of vulnerable artifacts in relation to these damage mechanisms. The observational study and literature review indicate that low-temperature pest control may be appropriate for a wider range of materials than was previously assumed.

1 INTRODUCTION

The National Museum of the American Indian (NMAI) is in the process of moving approximately 168,000 ethnographic objects and 632,000 archaeo-logical artifacts from outdated facilities in New York City (the Research Branch) to new facilities near Washington, D.C. (the Cultural Resources Center). An integral step in this move is to carry out a preventive pest management protocol to minimize the possible transfer of live insect pests within the collections to the new facility. For much of the collection, the preventive method is to treat objects with low temperature prior to relocating. Included in the vast number of objects treated are certain “borderline” types of materials for which low temperature was feared to be detrimental in theory, but to which experience and anecdotal evidence showed no damage.

Low-temperature (in the range of –20°C to –30°C) pest eradication in conjunction with an integrated pest management system has been the preferred method for museum pest control since the mid-1980s (Jessup and Ballard 1997; Strang 1997), in part as a reaction to federally mandated legislation limiting the use of pesticides. Subsequent development of both anoxic environments and the use of thermal methods has produced important applications in museum pest control. However, the ease, nontoxicity, speed, cost effectiveness, and definitive kill provided by low-temperature pest control continue to make it the favored pest control process whenever possible.

The existing conservation literature emphasizes the aspects of proper temperature, freeze duration, insect resistance, condensation, and practical low-temperature procedures. Little has been published about damage to artifact materials, although several references give lists of materials that are not recommended for this treatment (Florian 1986b for lists and procedures; Berkouwer 1994; Raphael 1994; Michalski 1996; Strang 1997; Baughman 1999). The types of potential damage feared include cracking, delaminating, fatty bloom, staining, corrosion, and fungal growth. Some NMAI objects considered vulnerable to low temperatures are not treated in the freezer but instead are managed with Vikane (sulfuryl fluoride), anoxic treatments, or careful inspection and isolation. The expense and time required for these alternatives, however, make low temperature the preferred option for the thousands of objects involved in the NMAI project. Some potentially vulnerable objects are being frozen at NMAI because they are part of a composite object where the risk of infestation seems greater than the risk of damage or because the object shows evidence of prior infestation.

Within the limitations of the move process, an observational study was undertaken to test the hypothesis that these materials are not damaged by low-temperature pest control. Four categories were investigated: materials in composite objects, cracked objects, lamellar objects, and waxy or oily objects. The results of this study, together with information about the mechanisms of damage due to low temperature and the characteristics of artifact materials at low temperature, contribute to an informed approach for the treatment of potentially vulnerable materials.

2 CONCERNS FOR MATERIAL CHANGES FROM FREEZING

Several categories of physical change were considered during this study to determine what mechanisms might be responsible for potential damage to artifacts during low-temperature treatment. References for low-temperature damage found in several nonconservation fields proved tantalizing but difficult to apply to the museum situation. The fields of cryogenics (the study of living systems at low temperatures) and low-temperature physics utilize a temperature range much colder than proposed for museum pest control. In general, Arctic studies, refrigeration engineering, and the food preservation industry deal with considerably more free water than pertains to the museum treatment situation. Freeze-thaw, dehydration, condensation, swelling, embrittlement, shrinkage, thermal shock, polymorphic phase change, and molecular alteration have all been mentioned by conservators as possible areas of concern. Some of these are relevant to museum pest control, and others are not. The field of materials science suggests factors of greater relevance.

2.1 MOISTURE AND HUMIDITY ISSUES

Little information is available to conservators about potential damage to museum objects from low temperatures. Most concerns about the treatment are theoretical, extrapolated from the extensive information available about the reaction of museum objects to changes in relative humidity and from empirical evidence from daily life (such as one’s home freezer). Some of these assumptions are incorrect. In a museum treatment situation using proper packaging, most objects lack sufficient moisture for freeze-thaw or dehydration mechanisms to occur. Inclusion of adsorbent buffering materials and the counteraction of shrinkage mitigates swelling as a concern, while proper bagging eliminates the danger of condensation on the object and creates a closed system. Conservation scientist Mary Lou Florian of the Royal British Columbia Museum has written extensively about moisture relationships and proper low-temperature protocol and included lengthy bibliographic references outside the field of conservation in her articles (Florian 1986a, 1986b, 1987, 1990a, 1990b).

2.1.1 Freeze-Thaw

Use of the term “freezing and thawing” to describe the museum pest control process should perhaps be replaced with the more accurate “warming and cooling.” The term “freezing” is loosely used in the conservation literature to imply temperatures below 0°C, and in this context does not necessarily imply a phase change from liquid (water) to solid (ice). Review of the scientific literature indicates ice does not tend to form in museum objects. A brief review of water dynamics is helpful in understanding several issues surrounding potential damage to artifacts.

Moisture content (MC) is the percent weight of water in relation to the dry weight of the material. Water activity (Aw) reflects the portion of water within the moisture content that can be used for “activity” such as chemical reactions, availability to microorganisms, or exchange of humidity between the material and its environment. Water activity is given as the ratio of vapor pressure of water in a material compared to pure water under identical conditions. Sometimes this number is multiplied by 100 and called the equilibrium relative humidity (%ERH). Equilibrium moisture content (EMC) is a measure of the amount of water in an object after it has reached equilibrium with its surroundings over time. Water can exist in many physical states on a continuum reflecting how strongly the water is bound to another material. On one extreme, it can be tightly bound in a single layer to the polar sites of molecules. This water does not freeze (Nomura et al. 1977). At the opposite extreme is free water. If sufficient free water were present in museum objects, the phase transitions between liquid water and solid ice implied by the terms “freeze” and “thaw” could cause damage from the expansion of ice. However, ethnographic objects in a museum setting generally do not have sufficient equilibrium moisture content to undergo the formation of ice. Most organic artifact materials in museum environments have 8–12% moisture content (Florian 1986b). Artifact material with equilibrium moisture content of up to 28% does not form ice at –20°C (Zachariassen 1985). For example, in beef dried to 22.5% moisture content, no ice formed regardless of temperature (Fennema 1981). The water present in most museum objects is physically adsorbed or chemically combined water and is therefore not available for ice formation. (Adsorption is the adherence of water molecules as a monomolecular layer, as distinguished from absorption, in which the penetration is deeper into the molecular structure.) Furthermore, free water in capillaries smaller than 30 micrometers (as in collagen) is physically altered and does not solidify above –40°C (Horne 1969). Even in fresh collagen (45–60% water), the water of hydration is still in a state of mobility at temperatures well below the freezing point of ordinary water, remaining unfrozen at temperatures as low as –50°C (Dehl 1970). In frozen muscle, approximately 20% of the water was considered unfreezable in nuclear magnetic resonance (NMR) studies (Taylor 1987).

When it does occur, ice formation is commonly known to cause freeze-thaw damage from the 9% expansion in volume that takes place as water changes from the liquid to the solid phase (Franks 1985). Other phenomena, however, are also related to the formation of ice. Living plants hold their shape in part due to “turgor pressure” or the pressure of water inside the cells of the plant tissues. At low temperatures, an increase in the permeability of the cellular plasma membrane (due to pressure from the 9% increase in volume as ice crystals grow) causes a loss of cellular water, thus turgor pressure and the subsequent “wilted” appearance of some frozen plant materials (Reid 1987). However, the most damaging problems associated with freezing are the “concentration effects.” As an aqueous solution freezes, water separates out of the mixture as ice, and the concentration of the remaining solutes increases (Taylor 1987). This result affects a variety of factors within the cell, including ionic strength, viscosity, oxidation-reduction potential, pH, salt concentration, and enzyme reactions. The majority of the literature associated with freezing damage focuses on these effects (Hawthorn 1968; Poulsen and Lindelov 1981; Kobs 1997). At low-moisture-content levels such as those present in most museum objects, the possibility of ice formation, loss of turgor pressure, and damage related to concentration effects is eliminated.

2.1.2 Dehydration

Dehydration does not occur in objects inside the freezer if there is insufficient free water to be lost (Florian 1986b; Strang 1997). The ability of air to hold moisture is temperature-dependent. The word “relative” in “relative humidity” refers to the relationship of moisture present to the maximum of it that air can hold at a given temperature. Wintertime air, for example, is drier than summertime air because cool air cannot hold as much humidity as warm air. When dry winter air is warmed inside a building, it is able to hold more humidity, and inhabitants of that building (including food, plants, and people) help provide the moisture to bring the air into equilibrium at a higher RH. Complaints of dry, itchy skin in the winter are often related to the ability of human skin to provide water for warmed, dry air “hungry” for moisture. The cold air inside the freezer is not “hungry” for moisture. The equilibrium moisture content in an adsorptive object actually tends to increase due to the decreased ability of the air to hold moisture. The relative humidity measured in freezer-bagged enclosures does not correlate to the experience of the object at the same RH in a standard room temperature situation. A reading of the RH measured in the enclosure must take into account the moisture the air has already given up to the object and buffering materials. In this case, the lower RH does not signify a situation where the object is being desiccated by a dry environment. On the contrary, reducing the temperature allows the object to slowly increase in EMC.

A review of the process called “freeze-drying” is helpful in understanding why museum objects do not dry out during low-temperature pest control. Freeze-drying is a process involving the removal of frozen water from an object by sublimation. In contrast to evaporation, where liquid water is turned to water vapor and carried off, sublimation is the removal of water vapor directly from ice without its becoming liquid. “Freezer burn” is the surface dehydration of poorly packaged foods caused by sublimation in the freezer. Freeze-drying is a more sophisticated process involving a vacuum in order to take advantage of the properties of water under low pressure. Under low pressure, water will vaporize at a lower temperature. That is, water does not need to be as hot to become water vapor. (This circumstance is related to the phenomenon of water boiling at a lower temperature at a high elevation due to the lower atmospheric pressure of thin mountain air.) With the use of a cold condenser and a gentle heating element, the air in the freeze-drying chamber is kept at a temperature slightly above the temperature of the frozen object, allowing water molecules on the object’s surface to break free and gather on the condenser as frost (Schmidt 1985). This treatment is used only when museum objects are wet and have sufficient free water to form ice and allow sublimation to occur.

2.1.3 Condensation

Condensation is a result of the reduced capacity of air to hold moisture as its temperature is lowered. It is this phenomenon that is observed on a car’s windshield in the winter. When the interior of a car is warmed, the warm air encounters the cold wind-shield, and a microclimate of cold air is created near the surface. This small cushion of cold air cannot hold the same level of humidity held by the warm air, and moisture condenses on the interior of the windshield. Turning on the air vent next to the windshield will alleviate the problem, moving the warm air away from the surface before it has the opportunity to cool.

Some artifact materials, such as wood and hide, are able to adsorb the humidity released by the air at low temperature and release it again when brought slowly to room temperature. Nonadsorbent materials, such as metals and stone, do not have that capacity and are vulnerable to condensation on their surfaces when cooled.(Frost is simply frozen condensation.) Condensation could potentially cause staining, migration of colorants, corrosion, or fungal growth. Addition of adsorbent packing materials such as crumpled tissue reduces the likelihood of condensation on nonporous objects, as adsorbent materials act as a buffer and adsorb available water vapor. Placing the objects in sealed plastic bags with most of the air removed reduces the amount of moisture available in the air for possible condensation. The sealed plastic bag also serves to prevent condensation on the cooled object as it returns to room temperature. Any condensation during warming would form on the outside of the plastic bag, following the model that condensation forms on the warm side of the warm/cool interface. Although polymer films, such as polyethylene bags, are slowly permeable to moisture, it occurs over a longer period of time (several weeks) than the bags would be in use for cooling (several days) (Strang 1997; Florian 1992).

2.1.4 Swelling

Swelling of materials is another consequence of the reduced ability of cold air to hold moisture. The excess moisture can be adsorbed by porous materials, and a small amount of swelling may take place. Again, this result can be mitigated by the inclusion of buffering materials to sacrificially adsorb and release the excess moisture. Wood, for example, swells at low temperature if it has exposure to open air. However, in the bagged situation, the equilibrium moisture content (EMC) change is not significant because the amount of water available for adsorption in the bag is small in relation to the amount that can be adsorbed (Florian 1990a, 1992). Furthermore, materials at low temperatures take longer to reach moisture equilibrium with the environment than the same materials at room temperature. Photographic films have been reported to take between 10 and 30 times longer to reach equilibrium at low temperature (Adelstein et al. 1997). At room temperature, white oak was found to take up to 80 days to completely adsorb or desorb moisture (Grattan and Barclay 1988). Experiments with textiles indicate wool required 14 days and silk more than 3 weeks to reach equilibrium at room temperature (Howell 1996).

2.2 PROPERTIES OF MATERIALS

The biggest potential risks faced by museum objects during freezing stem not from moisture-related issues but from the properties of materials at low temperatures and the mechanisms of cold-induced damage. Important factors include the coefficient of thermal expansion, stiffness, thermal conductivity, and strength of the material. Thermal cycling and the magnitude of temperature change can pose potential dangers. Geometry, aging, residual stresses resulting from manufacture, and the history of each unique object can also play significant roles. An understanding of the damage mechanisms will contribute to a more informed consideration of the risks and a logical approach to decision making.

2.2.1 Embrittlement

Embrittlement occurs at temperatures used for pest control because the molecules are resistant to motion. Increased tendency to fracture is related to this reduced ability to deform. So-called “glassy” behavior occurs when the molecules do not vibrate enough to bump past each other during the application of stress. The “glass transition temperature” (Tg) is the range of temperatures at which molecular motions become slower than the rate at which temperature is changed and the material no longer has sufficient time during cooling to remain in equilibrium. The material then changes from soft and rubbery to solid and glassy with a decrease in specific volume (shrinkage). The Tg is sometimes given as a range because it can be affected by factors such as the age of the material (aging increases the Tg) or rate of cooling (slower cooling gives a lower Tg). Below Tg, brittle fracture can occur by crack propagation. Elastic deformation tends to occur above Tg.

Conservators are perhaps most familiar with the concept of Tg in relation to adhesives. AYAA Poly (vinyl acetate) (PVA) adhesive, for example, has a lower Tg than Paraloid B-72, and is therefore more flexible at room temperature and preferred for use in situations where more flexibility in the join is desired, such as repairing feather quills. However, in an archaeological field setting, the low Tg of PVA may cause slumping of reconstructed ceramics. Thus the higher Tg of Paraloid B-72 is preferred.

Stiffness describes the amount of elastic deformation resulting from a given applied stress. “Elastic” behavior describes the ability of a material to deform under stress and still return to its original conformation. Objects with a high elastic stiffness tend to be brittle. Stiffening of most elastomers occurs below –20°C, while the brittle point does not begin to occur until –50°C (Sehgal and Lindberg 1973). Examples of materials that become brittle in this temperature range include rubber, resin varnishes, linseed oil films (oil paint), synthetic polymers, acrylic paint, and soft vinyl (Mecklenburg and Tumosa 1991; Michalski 1991). Linseed oil, for example, becomes fully glassy at –30°C (Michalski 1991). Although elastic stiffness induced by cooling is usually reversible with warming, materials are potentially vulnerable to structural damage until sufficiently warmed. Dangers could include vibrational stresses from motors inside faulty freezers, rough handling when moved while cold, and even the weight of the object itself (as in the case of a load-bearing adhesive).

Glass is an example of a material with a high elastic stiffness. In addition, glass is a poor conductor of heat and has a low resistance to crack growth. Generation of small surface cracks is likely to occur from cooling during manufacture as the surface goes into tension. Repeated exposure to low temperatures could result in one of two outcomes for these cracks: “ratcheting” or “shakedown.” Ratcheting describes the accumulation of plastic strain. Each time the crack is opened and closed, the crack grows. Damage evolution due to thermal cycling is known as “thermal fatigue” and will eventually lead to macroscopic failure. The other option, shakedown, involves a reduction of the incremental strain per cycle. Most of the damage in this process happens the first time the object is exposed to low temperature, and each subsequent freezing cycle results in less damage per cycle (Elzey 2001). It is also important to include aging as a factor in considering crack formation and growth. An object repeatedly exposed to freezing temperatures during its use in the Arctic may not tolerate thermal cycling after many years in controlled storage.

2.2.2 Shrinkage

Practically all materials shrink as temperature is lowered because of the reduced vibration on the atomic or molecular scale. (Think of how gas expands during heating due to the more active motion of its molecules.) The decrease in vibration causes the molecules to have a smaller range of motion and thus to take up less space. The “coefficient of thermal expansion” (CTE) is a measure of this change, expressed as a ratio of change in length per degree Celsius compared with the base length at some reference temperature (cm/cm/°C). How much a material might shrink is dependent on the strength of the interatomic bonding. Objects with strong chemical bonds, such as metals and ceramics, expand and contract less with changes in temperature than objects with weaker bonds. Rabbit skin glue, for example, with a CTE of .000025 cm per degree Celsius, will shrink only 0.1% when cooled from 20°C to –20°C (Mecklenburg and Tumosa 1991). In his discussion of paintings, Michalski cites 3% elongation as the elastic limit beyond which a polymer cracks (Michalski 1991).

Low-temperature treatment of composite objects gives rise to a risk of damage due to CTE mismatch if the two materials have different coefficients of thermal expansion. Internal stress, deformation, and damage could occur as the composite object is heated or cooled. There are published tabulations for expansion coefficients of some common materials, but there may be no data for many materials in aged or altered condition, or no data in the appropriate temperature range, or simply no data at all. Often materials are simply categorized as high or low relative to each other. During cooling, the low CTE material goes into tension while the high CTE material is in compression and in danger of cracking or delaminating.

CTE differences or mismatch can also be seen within a single material, particularly those that demonstrate anisotropy. The bonds in anisotropic materials are direction-dependent and expand to different degrees in different directions. Examples include materials with a complex structure that tend to crack in a preferential direction, such as wood, bone, tooth, and lamellar structures. Since the rate of freezing does not affect the CTE mismatch, it is not possible to mitigate damage by controlling the rate of freezing.

Cracking is not the only manifestation of CTE mismatch. If the high CTE material is more vulnerable, deformation or crushing may occur as the material goes into compression. A high CTE material sandwiched between two layers of low CTE material may be extruded by pressure from the surrounding material.

At sufficiently high stress, materials lose their ability to deform elastically, resulting in either failure or plastic deformation. Unlike elastic deformation, which is fully recovered when the applied stress is removed, plastic deformation is permanent. Plastic deformation of capillary structure and loss of water bonding sites is thought to contribute to the loss of moisture-regain ability in skins and furs exposed to cold storage (Pool 1997). Plastic deformation of cell structure and subsequent depletion of gas is thought to contribute to observed Ethafoam shrinkage in the freezer. The inability of air to replace the lower molecular weight gas that may have been squeezed out of the individual Ethafoam cells may also be a factor (Elzey 2001). Low RH is a far more common cause of shrinkage in artifacts than the effects of low temperature alone (Michalski 1991).

2.2.3 Thermal Shock

Thermal shock is the condition resulting when rapid temperature change leads to excessive internal stress resulting in damage or failure. It is the phenomenon that occurs when cold water is poured over a hot ceramic plate, causing it to shatter. The magnitude of the stress is determined by the overall change in temperature, the rate of cooling, the size of the object, and the material’s CTE, elastic stiffness, conductivity, and strength. Materials with high CTE, high elastic stiffness, low thermal conductivity, and low strength and that are exposed to a large overall rapid change in temperature are most at risk for thermal shock. Although most organic materials possess high coefficients of thermal expansion, conduct heat poorly, and are held together by low-strength secondary bonds, they have the advantage of very low elastic stiffness and are comparatively resistant to the effects of thermal shock. Inorganic materials found in composite objects may be more at risk. Ceramics, for example, combine high strength, high elastic stiffness, and poor conductivity. Although they have a low CTE, they are at higher risk for thermal shock. Table 1 is a synthesis of information mentioned in the literature and attempts to describe several key properties influencing the probability of thermal shock. “High,” “medium,” and “low” describe how these materials compare to one another for each property.

Table of Factors Involved in Thermal Shock

For table, see link

http://aic.stanford.edu/jaic/articles/jaic42-02-002.html

2.2.4 Polymorphic Phase Change

Phase change refers to a change in state, such as from a solid to a liquid, or liquid to gas. “Polymorphic” phase change implies a change from one solid state to another, often seen in metals at elevated temperatures. Polymorphism implies an ordered, crystalline structure. Many polymers and organic materials do not undergo polymorphic phase changes because they lack the tightly packed, regular 3-D arrangement of atoms that facilitates the change from one formal crystalline arrangement to another. If organic materials do become crystalline, as some polymeric materials may, then polymorphic phase changes do become possible. Temperature change may cause noncrystalline materials to assume a crystalline formation. Such a phenomenon can be observed in the crystallization of olive oil in one’s home refrigerator. In reference to elevated temperatures, Ellen Pearlstein describes the fatty bloom mechanism as follows:

Polymorphism, the condition in which the same substance can assume different crystal forms, is shared by triglycerides, long chain acids, esters, alcohols, and paraffins. … Temperature conditions influence which polymorphic form is most stable. Fats and waxes, which are semi-solid at room temperature, will continue to respond to subtle temperature changes with phase transitions, reaching a new equilibrium at a new temperature … a varied temperature history and the inclusion of impurities in a sample would make predictions of polymorphic behavior almost impossible. (Pearlstein 1986)

Observation of fatty bloom on a dressed leather saddle treated for pest control suggests that polymorphic phase changes might occur in museum objects at low temperature (Baughman 1999). Leather dressing often includes Neat’s foot oil from which the solid triglyceride portion has been removed through chilling, causing the solids to rise to the surface of the oil. Solid triglycerides remaining in Neat’s foot oil dressing may cause spew at low temperature (Fogle 1985).

Rubber is another material reported to undergo changes at low temperature. The rate of crystallization of rubber increases with decreasing temperature, reaching a maximum at approximately –25°C. Rubber that is crystallized is characteristically inelastic and may have hard or “crunchy” cracked surfaces. This alteration is sometimes reversible upon warming (Baker 1995).

Allotropes are polymorphs of elements, and some occur at low temperature. Tin disease (tin pest, tin blight, tin plague) is one such example. One pure tin allotrope, beta tin, is the shiny stable white metal seen at room temperature. The alpha tin allotrope (a nonmetallic crumbly gray powder) becomes the more stable form as temperatures decrease, reaching a maximum at –30°C. Upon warming, crystalline faults form, exacerbating the problem (Elzey 2001). Tin disease is inhibited by as little as 0.1% bismuth, antimony, or lead, the typical alloying metals used with tin. Most of our museum materials (such as tin cone tinklers found on Native American artifacts from the Great Plains) are alloys and therefore safe from polymorphic phase change in the freezer. However, the textbook example of tin disease involves Napoleon’s attempted 1812 winter invasion of Moscow, which failed in part because of the disintegration of the tin buttons on the soldiers’ clothing.

2.2.5 Molecular Alteration

The technology for studying proteins at low temperature in the absence of ice formation has been developed only within the past decade. Previously, scientific knowledge of low-temperature “denaturation” or unfolding of proteins was based on extrapolations from high-temperature experiments. Current research indicates that the denaturation of proteins has different causes at high and low temperatures and results in different disruptions of the molecule (Fahy 1995; Franks 1995). “Low temperature” studies of biological phenomena rarely involve temperatures below –70°C and often involve temperatures just below –0°C (Douzou 1977; Taylor 1987). Conformational stability in proteins is dependent on a complex energy balance involving a variety of intermolecular forces. Cooling weakens some forces, such as hydrophobic interactions, but enhances others, such as hydrogen bonding. These kinds of changes in the molecule may not be completely reversible upon warming and could alter some of the identifying characteristics of the protein (Taylor 1987). Many of these studies, however, involve freezing proteins with significant moisture content and suffer from the associated concentration effects. Simple exposure to low temperature exclusive of moisture-related complications is thought to cause a general instability that renders the protein susceptible to the influence of other factors leading to denaturation. However, most of those factors involve water content and ice formation (Taborsky 1979; Taylor 1987).

Although the rate of most chemical reactions tends to decrease with decreasing temperatures, according to the Arrhenius equation (Mills and White 1987), oxidation of lipids is an important exception. Autoxidation of unsaturated fatty acids, however, can be accelerated by low temperatures in the range used for pest control (Franks 1985). Autoxidation of lipids in foods is associated almost exclusively with unsaturated fatty acids such as are found in vegetable oils (Karel 1985). Lipids contain a wide variety of fatty acids that differ in chemical and physical properties as well as in their susceptibility to oxidation. Lipids in the NMAI collection include animal fats, plant waxes, beeswax, avian preen oil on feathers, and lanolin in wool. These materials have complex combinations of lipids that usually include a percentage of unsaturated fatty acids. The autoxidation of saturated fatty acids is very slow and slower still at low temperature. Oxidation may also be catalyzed by enzymes, although the definition of enzymes as “proteins produced by living organisms functioning as biological catalysts in living organisms” (Roberts and Caserio 1977) calls into question whether there are any active enzymes remaining in museum objects. Furthermore, some enzymatically catalyzed oxidation in lipids is influenced by solute concentration effects that allow enzymes and substrates to come into contact (Karel 1975; Reid 1987). Museum objects that cannot form ice are unlikely to face these problems.

Caution must be exercised in extrapolating data from other fields. Agricultural research, for example, is concerned with the longevity of biological tissues as a nutritional resource and issues such as flavor and texture preservation. The behavior of fresh fish muscle at low temperatures and its purpose upon thawing is very different from the behavior of an aged, dried fish skin artifact. The cryogenics field is concerned with the viability of tissues at low temperatures in the colder range of –80 to –196°C (Reid 1987). Both fields focus closely on the continuation of biological function and address issues of decomposition and cell death from a point of view that considers loss of structural integrity a somewhat secondary concern. For these fields, their objectives have already been lost at the level that museum freezing for pest control is addressing.

The loss of moisture-regain ability due to changes on the molecular level is another realm of potential problems for organic materials (Kronkright 1990; Pool 1997). The term “hysteresis” is used to describe nonlinear input-output systems because of material memory. Imagine an experiment measuring water content at different relative humidities. The experiment could be set up in two ways: the material may begin dry and measurements taken as it adsorbs water, or the material may begin wet and measurements taken as it desorbs water. Interestingly, at a given RH, the water content of the material is higher when it is in the process of desorbing than when it is in the process of adsorbing (Tímar-Balázsy and Eastop 1998). This finding is thought to be because polymers are at a more stable energy state with higher moisture content and are not as willing to give up moisture as they are to take in moisture. This phenomenon of adsorption and desorption rates relying on moisture history is one example of hysteresis. At low temperatures, molecules with potential water-holding sites may draw closer together and bond, creating a reduced capacity to hold water in the future. Water activity and moisture content are related by a curve known as a “moisture sorption isotherm.” It has been reported that sorption ability decreases with increase of cold storage time (Wolf et al. 1972). Long-term cold storage of furs and skins in an open system (not in a sealed bag) has been reported to cause a loss in moisture-regain ability (Pool 1997). Another study suggests that low-temperature treatment for pest control (a comparatively brief period of time) has a minimal initial effect on shrinkage temperature of collagen (Williams et al. 1995). There appears to be a difference between damage from short-term low-temperature exposure and long-term cold storage.

3 VULNERABLE MATERIALS IN ARTIFACTS

Several categories of artifacts were systematically observed in this study because they exhibited characteristics or flaws making them potentially vulnerable to the damage mechanisms described above. The following sections will discuss the potential for damage in artifacts with multiple material compositions, cracks, lamellar structures, waxy or oily elements, or cultural sensitivity.

3.1 MATERIALS IN COMPOSITE OBJECTS

The vulnerability of composite objects involves two areas of concern. The first category includes objects featuring different materials in close contact inhibiting independent movement of each material according to change in temperature or humidity. Tension may be built into an object during natural formation of the material (such as a tooth) or human creation of an object (such as a drum). Cracking, splitting, or warping may occur when one material is restricted by another. The second category involves materials that are not generally frozen (particularly inorganics such as metals, glass, ceramics, or stone) attached to materials that are good candidates for freezing. Garments with metal, glass bead, or tooth adornments are common. If the packing material or the more thermally robust part of the composite cannot mitigate the effect of the freezing environment, there is the potential for the vulnerable material to suffer from cracking or surface condensation. Condensation from poor packaging may result in staining, corrosion, or other changes in surface characteristics. Examples of vulnerable materials in composite objects include rawhide or sinew wrappings (arrows, hammers, snowshoes, etc.), metal (buttons, cone tinklers, brass tacks, inlay, etc.), tooth (garments, masks, jewelry), ceramic (beads, pipes), stone (beads, pipes), glass (beads), wood objects with inlay or tight joinery, and wax on wood or other organic substrates.

3.2 CRACKED OBJECTS

Shrinkage, swelling, embrittlement, and other phenomena in the freezer may lead to propagation of existing cracks or formation of new ones, especially in materials made up primarily of inorganic compounds. Ivory, tooth, and bone are of special concern since they have been shown to crack under changes in humidity, apparently from the stresses of shrinking and swelling. Tooth, bone, ivory, and baleen contain both inorganic and organic components that behave differently under temperature and humidity changes. Bone, for example, is anisotropic (it has a higher percentage of change in the long axis) and responds to environmental changes differently in different directions (Williams et al. 1993). Cracking is most easily caused in thick objects (such as stone, glass, and ceramic) having poor thermal conductivity, a high CTE, and high elastic stiffness when they are subjected to large, sudden changes in temperature. Beads with the tiny cracks associated with glass disease may be at additional risk because of their sensitivity to changes in humidity. Improper packing for low-temperature treatment could theoretically expose the glass to the elevated RH that occurs with decreased temperature (see sec. 2.1.3). Glass disease involves deterioration of the glass structure from leaching out of water-soluble components with flawed compositions created during manufacture (Lougheed 1988; Erhardt and Mecklenburg 1994). Michalski mentions that craquelure on painted or coated wood may crack further at –50°C (Michalski 1996). Candles are thought to crack if placed in the freezer, suggesting thick wax layers may be vulnerable. Some botanicals such as seeds or gourds might have the potential to crack, although the National Museum of African Art recently treated 60 gourds, including some with crack and ethnographic repairs, and noted no visible damage (Hornbeck 2001). The cracking danger in the freezer does not seem to be from low temperature alone as much as from mishandling while cold objects are embrittled. Examples of materials vulnerable to cracks include bone, tooth, ivory, diseased glass, painted or coated wood, plant materials, wax, and inorganic materials such as metal, ceramic, and stone.

3.3 LAMELLAR OBJECTS

Delamination is the peeling apart of materials with a layered structure. Examples of particular concern include painted objects such as masks and furniture, particularly if the pigment is well bound in media that will behave differently from the substrate. Amorphous and semi-amorphous polymer media (oil, varnish, glue, gum) can suffer shrinkage on the scale of 0.7% per 70°C decrease in temperature. Leaner paints with less binder and a larger percentage of pigment, however, fare better with shrinkage in the range of 0.4% per 70°C decrease in temperature (Michalski 1996). It is interesting to note that certain woods, such as cedar, cypress, and redwood, hold paint better than others, due in part to their dimensional stability but also because they are relatively porous and the wood-paint bond is thought to be largely mechanical (Mecklenburg et al. 1997). Another area of concern involves adhered or glued objects such as feather tipping on war bonnets, inlaid objects, furniture joinery, and past treatments. Most adhesives are stronger, more brittle, and more reactive to increases in RH at low temperatures (Erhardt and Mecklenburg 1994; Erlebacher et al. 1992). Joins that are under stress are at additional risk for failure as the adhesive becomes brittle at low temperature. The adhesive and adherend may also shrink or swell at different rates, causing failure. Objects with accretions from burial or use may be vulnerable for similar reasons. There have been reports of successful low-temperature treatment of leather with adhesive repairs, including BEVA 371 film, silicone adhesive SF2, and wheat starch paste mixtures (Kite 1992), as well as the successful low-temperature treatment of Japanese lacquer wares (Tanimura and Yamaguchi 1995). Shell (turtle shell, marine shell, snail shell) is thought to be potentially vulnerable to damage at low temperature due to its lamellar structure. This natural lamellar structure provides areas of weakness for stresses to be released if shrinking or swelling occurs. This damage could manifest as an opening up of these layers, with associated peeling and loss. Byne’s disease is another source of concern: the appearance of powdery deterioration on the surface of a shell could indicate that the calcium carbonate has reacted adversely with acid vapors off-gassing from wooden shelves or cabinets, forming hygroscopic salts that could swell in elevated humidity (Tennent and Baird 1985). Horn, as a keratinaceous material similar to hair, has the ability to absorb limited amounts of moisture. However, the lamellar structure of its growth makes it prone to crack with age, and it is these cracks and microcracks that may be propagated if stressed. Baleen is similar to horn, but further calcified. Changes in RH between 25% and 85% do not seem to affect the dimensional stability of skull bones in mammals (Williams et al. 1993). Teeth, which are hygroscopic, anisotropic lamellar structures, suffer more from low RH than from temperature changes. If damage occurs, canines are more prone to crack than molars, in part because the hollowness of molars constrains movement less than the more solid interiors of canines (Williams 1991). It is interesting to note that industrial cleaning techniques recently developed for large wooden surfaces such as floors employ low temperature expressly to force failure between layers, including wood, dirt, wax, varnish, and overpaint (Piening and Schwarz 1999). It is worth repeating that proper packaging should eliminate the elevated humidity that occurs with low-temperature treatment (see sec. 2.1.3). Examples of materials vulnerable to delamination include adhesive joins and repairs, painted or gilded objects (masks, furniture, beads), turtle shell, marine shell, snail shell, horn, baleen, bark, resins, and accretions.

3.4 WAXY OR OILY OBJECTS

The possibility of waxy, powdery, or crystalline formations developing on the surface of some materials during treatment is another area of interest (see sec. 2.2.4). Waxes, oils, and fats found in some objects (oiled ropes, food bowls with residues, dressed leather) may undergo a polymorphic (solid-to-solid) phase change during cycled changes in temperature, resulting in an opaque, powdery wax formation on the surface (Pearlstein 1986). Another explanation suggests that bloom may be the result of having materials with different coefficients of thermal expansion in contact with each other. For example, if a high CTE wax is sandwiched between two low CTE fibers (or vice versa), the wax will be squeezed (extruded) from between the fibers as temperature is increased (Elzey 2001). Spew from dressed leather exposed to low temperature for pest control has been reported (Baughman 1999). Cold temperatures may also cause waxes to become brittle (Victoria and Albert Museum 1970). Examples of materials vulnerable to bloom include bark, botanicals, wooden food dishes, dressed leather, wood with waxed surfaces, and oiled ropes.

3.5 OBJECTS WITH NONTANGIBLE SENSITIVITIES

Low-temperature treatment may be inappropriate for objects with cultural sensitivity determined by traditional care. Some objects are considered to be sacred or living members of certain cultural groups. The bagging required for a low-temperature treatment may constitute mistreatment from a traditional care perspective. Some Native American medicine bundles at NMAI are sometimes allowed to deteriorate naturally and be consumed in isolation from other objects within the museum environment. Examples of materials with potential cultural sensitivity include bundles, masks, pipes, sacred or ceremonial objects, medicine objects, fragments of human remains, and associated funerary objects.

4 THE PREVENTIVE FREEZE PROCESS AT NMAI

Both the Research Branch and the Cultural Resources Center are equipped with large walkin freezers. All objects packed at the Research Branch for the move are lightly surface-cleaned with a vacuum and secured on a travel mount. Some are tied down with cotton twill or Teflon tape to corrugated pallets with polyethylene foam supports, while others are placed in small boxes with acid-free tissue, bubble wrap, or polyethylene foam padding. These housings are then bagged in clear polyethylene plastic sealed with tape and grouped in larger cardboard boxes. These large boxes are wrapped with an additional layer of polyethylene and securely taped. During the move process (but not during this study), the boxes are placed in the Research Branch freezer at approximately –20ºC for five days. Boxes are then loaded on a climate-controlled truck for shipping to the Cultural Resources Center.

For the purposes of this study, freezing for pest management was done at the Cultural Resources Center instead of the Research Branch to eliminate possible damage in transit as a variable and allow condition after travel and before freezing to be assessed. The freezer at the Cultural Resource Center is a Bally pre-engineered walk-in freezer averaging a temperature of –40ºC. From the perspective of insect mortality, there is no benefit to temperatures below –40ºC, and lower temperatures may put the objects at greater risk of damage (Strang 1997). This temperature is lower than the –20ºC routinely used at the Research Branch for the NMAI move process. The freezer used for the observational study is a two-stage 10HP refrigeration system with a 45-minute defrost cycle every 6 hours. Freezers with defrost cycles are not typically recommended for pest control because during the defrost cycle they tend to rise above temperatures required to kill pests (Florian 1990a). Two ACR Systems Smart Reader 2 dataloggers were placed in the freezer with the objects on two occasions. Data from this equipment indicate that the temperature in the freezer drops from approximately 20ºC (room temperature) to approximately –40ºC over a two-hour period. This rapid drop is key to preventing cold acclimation in insects (Florian 1986b; Strang 1997). Temperatures were recorded as low as –45.8ºC. Defrost cycles were never warmer than –23ºC, safely below the recommended temperatures for insect mortality. The air inside the boxes returns to room temperature over a period of three to six hours after removal from the freezer. Relative humidity below 0 degrees is difficult to monitor because of the reliance of the datalogger on nonfrozen moisture for accurate readings.

5 THE OBSERVATIONAL STUDY

Objects for this study were selected at the Research Branch from among those slated for freezing and that fell into the previously described categories of concern. Additional samples were taken from the collection of NMAI “fix-it shop” materials used in the past for restoration purposes but now kept in the conservation laboratory for mock-ups and experiments. Table 2 lists the categories of materials observed for each object, and table 3 provides a description of “fix-it shop” materials observed. None of the study objects had been previously frozen at the Research Branch. Records for earlier low-temperature infestation treatments were not available. Upon arrival at the Cultural Resources Center, each object was inspected and documented with 35 mm color print details. For this project, a Nikon 6006 automatic 35 mm camera, a Nikon AF Micro Nikkor 60 mm lens, and a cameramounted Nikon Macro Speed Light SB-29 ring flash were used to ensure consistently controllable lighting. Kodak Royal Gold 200 color print film was chosen for its high quality and fine grain permitting good sharpness and contrast. Measurement of cracks, particularly on anisotropic materials, proved highly subjective with the available equipment. Even with a fine pair of calipers, fading of cracks into the grain of the mate-rial made it difficult to have confidence in the measurements. Visual comparison became the basis of observation. Detail photographs were taken as close as the lens would allow, and this distance proved to be at the threshold of easy visibility with the naked eye. Objects were packed according to normal move protocols described above, and put into the freezer for 6 days. After removal from the freezer, boxes were allowed to acclimate for at least 24 hours. Objects were then unpacked and compared to the prefreezing color prints. In cases where the outcome was ambiguous, a postfreezing photograph was taken under identical lighting conditions to compare with the initial print. In cases where the outcome was particularly illustrative, a postfreezing photograph also was taken. Table 4 documents the results of the three object groups put into the freezer during this study.

Materials Observed

For table, see link

http://aic.stanford.edu/jaic/articles/jaic42-02-002.html

Cultural Resources Center (CRC) Conservation Laboratory “Fix-It Shop” Collection (artifact materials not part of accessioned museum objects)

For table, see link

http://aic.stanford.edu/jaic/articles/jaic42-02-002.html

6 CONCLUSIONS

The observational study of vulnerable ethnographic material frozen at NMAI indicated no structural failure or visible surface changes to the objects. Low-temperature treatment conditions for this study were more extreme than recommended, in terms of both temperature and duration. Further evidence that encourages a cautiously optimistic attitude toward freezing can be found in several articles addressing museum storage in cold climates (Gates and Thorp 1982; Lafontaine 1982). So-called “humidistatically controlled heating” aims to control the RH of museum storage buildings in northern climates during the winter months, based on the principle that the RH of a constant volume of air with a given moisture content can be controlled by adjusting the temperature. No damage to objects has been reported, although vulnerable materials do not tend to be stored in these buildings. It is important to make the distinction between open systems such as these and the more controlled closed systems achieved with a sealed bag in low-temperature pest control.

Exploration of the literature and consideration of materials science issues raise two areas of concern. One involves the likelihood of repeated freezing cycles for some objects, particularly those actively loaned or exhibited and therefore subjected to low-temperature treatments with each re-entry into the museum collection. Experiments involving wood (Starecka and Mieczyslaw 1986; Erhardt et al. 1996), textiles (Dawley 1993; Holt et al. 1995; Jansson and Shishoo 1998; Peacock 1999), paper (Björdal 1998), synthetic fishing gear (Toivonen 1992), and insect collections (Rawlins 2001) suggest no significant structural damage occurs with repeated freezing cycles for pest control. It has been asserted that repeated cycling within the range of plastic deformation has no structural effects on most museum objects (Tumosa et al. 1996). Herbaria and natural history museums seem to have more of a tradition of successfully freezing collections on a regular basis than fine art museums do (Florian 1990b;Tanimura and Yamaguchi 1995; Shchepanek 1996;Ackery et al. 2000). One of the most encouraging examples comes from entomologist John Rawlins of the Carnegie Museum of Natural History, where 22,000 drawers of insect specimens are preventively exposed to –28ºC for two cycles every 18 months with no observed damage to pigments or structure and no microfractures seen under a scanning electron microscope (SEM). Of particular interest is the fact that these specimens are positioned while damp and then kept at 30–40% RH. Exposure to high RH or condensation in the freezer would cause wings and antennae to droop, and this change has not been observed (Rawlins 2001).

Freezing Report

For table, see link

http://aic.stanford.edu/jaic/articles/jaic42-02-002.html

The second area of concern involves the permanent physical changes that theoretically could occur (and perhaps accumulate) on a molecular level but remain invisible to the naked eye, such as loss of strength, loss of elasticity, distortion, crystallization, molecular alteration, and denaturation. In some cases there may be synergistic effects in which interrelated damage mechanisms combine to cause further problems.

While low-temperature treatment remains the best solution when ethnographic artifacts are actively infested, the need for preventive low-temperature exposure for objects entering and re-entering the museum environment is less obvious. Museum staff must weigh the potential risk for devastating loss through insect damage against the possible cumulative damage posed by repeated low-temperature exposure. Responsible prevention must include consideration of factors such as the quality of integrated pest management in the exhibit space or requesting institution, packaging and shipping conditions, duration of possible exposure to infested environments, ability of staff to perform adequate visual inspection, and the susceptibility of artifact material to insect pests.

 

ACKNOWLEDGEMENTS

Many thanks to Dr. Dana Elzey of the Department of Materials Science and Engineering at the University of Virginia, and the staff of NMAI, including Marian Kaminitz, Emily Kaplan, Jessie Johnson, and Leslie Williamson, for their support and feedback. I would particularly like to acknowledge Mary Lou Florian for her excellent work on this topic. Thank you to the Andrew W. Mellon Foundation for making this research possible.

REFERENCES

Ackery, P. A., A.Doyle, and D.Pinniger. 2000. Are low temperature pest disinfestation procedures safe? Biology Curator18:28–30.

Adelstein, P. Z., J. L.Bigourdan, and J. M.Reilly. 1997. Moisture relationships of photographic film. Journal of the American Institute for Conservation36:193–206.

Baker, M. T.1995. Thermal studies on ancient and modern rubber: Environmental information contained in crystallized rubber. In Resins: Ancient and modern, ed. M. M.Wright and J. H.Townsend. Edinburgh: Scottish Society for Conservation and Restoration. 53–56.

Baughman, M.1999. Approaches to insect problems in paper and books. Austin: Harry Ransom Humanities Research Center. http://www.hrc.utexas.edu/cons_web/bug_monitoring_99.html (accessed 2001).

Berkouwer, M.1994. Freezing to eradicate insect pests in textiles at Brodsworth Hall. Conservator18:15–22.

Björdal, L.1998. Effects of repeated freezing on paper strength. Proceedings of the Third Nordic Symposium on Insect Pest Control in Museums. Stockholm, Sweden: Naturhistoriska riksmuseet. 54–56.

Dawley, C. A.1993. The effect of conservation freezing treatments on selected properties of wool. Master’s thesis. Edmonton: University of Alberta. Department of Human Ecology.

Dehl, R. E.1970. Collagen: Mobile water content of frozen fibers. Science179(3959):728–39.

Douzou, P.1977. Crybiochemistry. New York: Academic Press. 152–59.

Elzey, D. M.2001. The effects of thermal cycling on the structure and properties of solids. Lectures given at the National Museum of the American Indian Research Branch, Bronx, New York, and Cultural Resource Center. Department of Materials Science & Engineering, University of Virginia, Charlottesville, Virginia.

Erhardt, D., and M. F.Mecklenburg. 1994. Relative humidity re-examined. Preventive conservation: Practice, theory and research. Preprints of the contributions to the Ottawa congress, September 12–16, Ottawa, ed. A.Roy and P.Smith. London: International Institute for Conservation. 32–38.

Erhardt, D., M. F.Mecklenburg, C. S.Tumosa, and T. M.Olstad. 1996. New versus old wood: Differences and similarities in physical, mechanical, and chemical properties. ICOM Committee for Conservation Preprints, 11th Triennial Meeting, Edinburgh, Scotland. Paris: ICOM. 903–10.

Erlebacher, J., E. D.Brown, M. F.Mecklenburg, and C. S.Tumosa. 1992. The effects of temperature and relative humidity on the mechanical properties of modern painting materials. In Materials issues in art and archaeology, vol. 3, ed. P. B.Vandiver et al. San Francisco: Materials Research Society. 359–70.

Fahy, G. M.1995. Cryobiology: The study of life and death at low temperatures. 21st Century Medicine (accessed March 2001).

Fennema, Owen. 1981. Water activity at subfreezing temperatures. In Water activity influences on food quality, ed. L. B.Rockland and G. E.Stewart. New York: Academic Press. 713–32.

Florian, M. L.1986a. The freezing process: Effects on insects and artifact materials. Proceedings of the 12th Annual IIC-Canadian Group Conference, Winnipeg, Canada. Ottawa: IIC-Canadian Group. 43–40.

Florian, M. L.1986b. The freezing process: Effects on insects and artifact materials. Leather Conservation News3(1):1–14.

Florian, M. L.1987. The effect on artifact materials of the fumigant ethylene oxide and freezing used in insect control. ICOM Committee for Conservation preprints, 8th Triennial Meeting, Sydney, Australia. Paris: ICOM. 199–208.

Florian, M. L.1990a. Freezing for museum pest eradication. Collection Forum6(1):1–7.

Florian, M. L.1990b. The effects of freezing and freeze-drying on natural history specimens. Collection Forum6(2):45–52.

Florian, M. L.1992. Saga of the saggy bag. Leather Conservation News8:1–11.

Fogle, S.1985. Neat’s foot oil in commercial products. Leather Conservation News1(2):8.

Franks, F.1985. Biophysics and biochemistry at low temperatures. Cambridge: Cambridge University Press.

Franks, F.1995. Protein destabilization at low temperatures. In Protein stability, ed. D. S.Eisenberg and F. M.Richards. Advances in Protein Chemistry 48. New York: Academic Press. 105–39.

Gates, M., and V.Thorp. 1982. Environmental control and artifact conservation in Arctic Canada. Proceedings of the 8th Annual IIC-Canadian Group Conference, Quebec, Canada. Ottawa: IIC-Canadian Group.20.

Grattan, D. W., and R. L.Barclay. 1988. A study of gap-fillers for wooden objects. Studies in Conservation33:71–86.

Hawthorn, J., ed.1968. Low temperature biology of foodstuffs. Oxford: Pergamon Press.

Holt, L., Y.Chen, and W.Dodd. 1995. The effect on wool fabrics of multiple freeze/thaw treatments for insect control. Textile Conservation Newsletter29:28–35.

Hornbeck, S.2001. Personal communication. Conservation laboratory, National Museum of African Art, Washington, D.C.: 20560.

Horne, R. A.1969. Marine chemistry. New York: Wiley-Interscience.

Howell, D.1996. Some mechanical effects of inappropriate humidity on textiles. ICOM Committee for Conservation preprints, 11th Triennial Meeting, Edinburgh, Scotland. Paris: ICOM. 692–98.

Jansson, P., and R.Shishoo. 1998. Effect of repeated freezing treatment on the mechanical properties of new wool. Proceedings of the Third Nordic Symposium on Insect Pest Control in Museums. Stockholm, Sweden: Naturhistoriska riksmuseet. 57–60.

Jessup, W. C., and M.Ballard. 1997. Integrated pest management. AIC News22(3):1–5.

Karel, M.1975. Stability of low and intermediate moisture foods. In Freeze drying and advanced food technology, ed. S. A.Goldblith, L.Rey, and W. W.Rothmayr. New York: Academic Press. 651–63.

Karel, M.1985. Lipid oxidation, secondary reactions, and water activity of foods. In Autoxidation in food and biological systems, ed. M. G.Simic and M.Karel. New York: Plenum Press.

Kite, M.1992. Freezing test of leather repair adhesives. Leather Conservation News7(2):18–19.

Kobs, L.1997. Designing frozen foods. Food Product Design (January).

Kronkright, D. P.1990. Deterioration of art made from plant materials. In Conservation of art made from plant materials, ed. M. L.Florian, D. P.Kronkright, and R. E.Norton. Marina del Rey, Calif.: J. Paul Getty Trust. 139–93.

Lafontaine, R. H.1982. Humidistatically controlled heating: A new approach to relative humidity control in museums closed for the winter season. Journal of the International Institute for Conservation, Canadian Group7(1–2):35–41.

Lougheed, S.1988. Deteriorating glass beads on ethnographic objects: Symptoms and conservation. In Symposium 86: The care and preservation of ethnological materials, ed. R.Barclay et al. Ottawa: Canadian Conservation Institute. 99–113.

Mecklenburg, M. F., and C. S.Tumosa. 1991. Mechanical behavior of paintings subjected to changes in temperature and relative humidity. In Art in transit: Studies in the transport of paintings, ed. M. F.Mecklenburg. Washington D.C.: National Gallery of Art. 173–216.

Mecklenburg, M. F., C. S.Tumosa, and D.Erhardt. 1997. Structural response of painted wood surfaces to changes in ambient relative humidity. Painted wood: History and conservation. Proceedings of a Symposium Organized by the Wooden Artifacts Group of the American Institute for Conservation of Historic & Artistic Works and the Foundation of the AIC (FAIC), Williamsburg, Virginia. Washington, D.C.: Wooden Artifacts Group of the American Institute for Conservation of Historic & Artistic Works and the Foundation of the AIC. 464–83.

Michalski, S.1991. Paintings: Their response to temperature, relative humidity, shock, and vibration. In Art in transit: Studies in the transport of paintings, ed. M. F.Mecklenburg. Washington, D.C.: National Gallery of Art. 223–48.

Michalski, S.1996. Freezing wood and parchment. Paper Conservation80:11–12.

Mills, J. S., and R.White. 1987. The organic chemistry of museum objects. London: Butterworths. 134–36.

Nomura, S., A.Hiltner, J. B.Lando, and E.Baer. 1977. Interaction of water with native collagen. Biopolymers16:231–46.

Peacock, E. E.1999. A note on the effect of multiple freeze-thaw treatment on natural fiber fabrics. Studies in Conservation44:12–18.

Pearlstein, E.1986. Fatty bloom on wood sculpture from Mali. Studies in Conservation31:83–91.

Piening, H., and R.Schwarz. 1999. Using cold on the cleaning interventions of surfaces: Three techniques. Kermes: Magazine for Conservation12(36):63–68.

Pool, M. A.1997. Preliminary analysis of the effects of cold storage on fur garments and mammal skins. Collection Forum13(1–2):25–39.

Poulsen, K. P., and F.Lindelov. 1981. Acceleration of chemical reactions due to freezing. In Water activity: Influences on food quality, ed. L. B.Rockland and G. F.Stewart. New York: Academic Press. 650–78.

Raphael, T.1994. An insect pest control procedure: The freezing process. Conserve-O-Gramno. 3/6. National Park Service. Washington, D.C.: U.S. Government Printing Office.

Rawlins, J.2001. Personal communication. Carnegie Museum of Natural History, Section of Invertebrate Zoology, Pittsburgh, Pa.

Reid, D. S.1987. The freezing of food tissues. In The effects of low temperatures on biological systems, ed. B. W. W.Grout and G. J.Morris. London: Edward Arnold. 478–87.

Roberts, J. D., and M. C.Caserio. 1977. Basic principles of organic chemistry. Reading, Mass.: W. A. Benjamin. 1270.

Schmidt, J. D.1985. Freeze drying of historic/cultural properties: A valuable process in restoration and documentation. Technology and Conservation (spring): 20–26.

Sehgal, S. D., and R. A.Lindberg. 1973. Materials: Their nature, properties and fabrication. Singapore: Kailash.

Shchepanek, M. J.1996. Observations of temperature and relative humidity during the cooling and warming of botanical specimens for insect pest control. Collection Forum2(1):1–7.

Starecka, D., and M.Mieczyslaw. 1986. Influence of freezing wood on its crushing strength. Annals of Warsaw Agricultural University, SGGW-AR. Forestry and Wood Technology33:43–46.

Strang, T. J.K. 1997. Controlling insect pests with low temperature. CCI Notes 3/3.

Taborsky, G.1979. Protein alterations at low temperatures: An overview. In Proteins at low temperatures, ed.OwenFennema. Advances in Chemistry Series 180. Washington, D.C.: American Chemical Society. 1–26.

Tanimura, H., and S.Yamaguchi. 1995. The freezing method for eradication of museum pest insects: The safe method for both the human body and artifacts: Experiment on Japanese artifacts and the present state of freezing method in western countries. Third International Conference on Biodeterioration of Cultural Property, Bangkok, Thailand. Bangkok: Thammasat University Press. 555–66.

Taylor, M. J.1987. Physico-chemical principles in low temperature biology. In The effects of low temperatures on biological systems, ed. B. W. W.Grout and G. J.Morris. London: Edward Arnold. 17–23.

Tennent, N. H., and T.Baird. 1985. The deterioration of mollusca collections: Identification of shell efflorescence. Studies in Conservation30:73–85.

Tímar-Balázsy, A., and D.Eastop. 1998. Chemical principles of textile conservation. London: Butterworth-Heinemann. 15–25.

Toivonen, A. L.1992. Investigation of the effects of cold winter conditions on fishing gear materials. Journal of the Textile Institute83(1):163–77.

Tumosa, C. S., M. F.Mecklenburg, D.Erhardt, and M. H.McCormick-Goodhart. 1996. A discussion of research on the effects of temperature and relative humidity on museum objects. WAAC Newsletter18(3):19–20.

Victoria and Albert Museum Conservation Department. 1970. The care of wax objects. Technical Notes on the Care of Art Objects, no. 4. London: Victoria and Albert Museum.

Williams, S. L.1991. Investigation of the causes of structural damage to teeth in natural history collections. Collection Forum7(1):13–25.

Williams, S. L., S. R.Beyer, and S.Khan. 1995. Effect of “freezing” treatments on the hydrothermal stability of collagen. Journal of the American Institute for Conservation34:107–12.

Williams, S. L., A. M.Wallace, and C.Jones. 1993. Effect of relative humidity on cranial dimensions of mammals. Collection Forum9(1):40–46.

Wolf, M., J. E.Walker, and J. G.Kapsalis. 1972. Water vapor sorption hysteresis in dehydrated food. Journal of Agricultural Food Chemistry20(5):1073–77.

Zachariassen, K. E.1985. Physiology of cold tolerance in insects. Physiological Review64(October): 799–832.

FURTHER READING

Abramov, Y. G.1975. Strength of fresh bone and bone preserved by freezing. Polymer Mechanics11(4):548–50.

Allington, C.1989. The extermination of insect pests by freezing. In Where to start, where to stop? Papers from the British Museum/MEG, Ethnographic Conservation Colloquium, occasional papers. London: Museum Ethnographers Group. 101–2.

Baker, M. T.1995. Ancient Mexican rubber artifacts and modern American spacesuits: Studies in crystallization and oxidation. In Materials issues in art and archaeology, vol. 4, ed. P. B.Vandiver et al. Pittsburgh: Materials Research Society. 223–32.

Brokerhof, A. W.1993. Icy insects: Freezing as a means of insect control. AICCM Bulletin18(3–4): 19–23.

Camuffo, D.1988. Surface moisture and conservation. European Cultural Heritage Newsletter on Research2(5):6–10.

Connell, J. J.1968. Freezing and frozen storage effect on protein of fish muscle. In Low temperature biology of foodstuffs, ed. J.Hawthorn. Oxford: Pergamon Press. 333–58.

Davies, J. D.1968. Freezing aspects in freeze drying of living cells. In Low temperature biology of foodstuffs, ed. J.Hawthorn. Oxford: Pergamon Press. 177–204.

Dean, R.1994. Cold, hard facts. Food Product Design (November).

Frankel, E. N.1998. Lipid oxidation. Dundee, Scotland: Oily Press. 216–20.

George, M. F., B. C.Cutter, and P. P. S.Chin. 1992. Freezing of water in hardboard: Absence of changes in mechanical properties. Wood and Fiber Science24(3):252–59.

Hand, H. M., C. O.Arah, D. K.McNamara, and M. F.Mecklenburg. 1992. Effects of environmental exposure on adhesively bonded joints. Construction and Building Materials6(4):227–34.

Hansen, E. F., S. N.Lee, and H.Sobel. 1992. The effects of relative humidity on some physical properties of modern vellum: Implications for the optimum relative humidity for the display and storage of parchment. Journal of the American Institute for Conservation31:325–42.

Hughes, J., C.Pearson, V.Daniel, and I.Cole. 1999. Monitoring of environmental conditions in a severe climate: How this can assist in development of conservation strategies for historic buildings and artifacts in Antarctica. ICOM Committee for Conservation preprints, 12th Triennial Meeting, Lyon, France. London: ICOM. 57–64.

Hughes, J.1988. The problems of preservation in a polar climate: The conservation of Sir Douglas Mawson’s huts at Commonwealth Bay, Antarctica. AICCM Bulletin14(3–4): 1–32.

Kolesnichenko, A. V., A. V.Zykova, O. I.Grabelnych, V. V.Tourchaninova, and V. K.Voinikov. 2001. The study of cold stress on lipid peroxidation at different mitochondrial respiratory chain complexes function in mitochondria. Maize Genetics Corporation Newsletter75(10):1–23.

Koslov, P. V., and G. I.Burdygina. 1983. The structure and properties of solid gelatin and principles of their modification. Polymer24:651–66.

Lafontaine, R. H., and P. A.Wood. 1982. The stabilization of ivory against relative humidity fluctuations. Studies in Conservation27:109–17.

McCormick-Goodhart, M. H.1996. Moisture content isolines and the glass transition of photographic gelatin: Their significance to cold storage and accelerated aging. Research techniques in photographic conservation. Proceedings of the Conference in Copenhagen, May 14–191995. Kobenhavn: Royal Danish Academy of Fine Arts. School of Conservation. 65–70.

Mecklenburg, M. F., C. S.Tumosa, and N.Wyplosz. 1995. The effects of relative humidity on the structural response of selected wood samples in the crossgrained direction. In Materials issues in art and archaeology, vol. 4, ed. P. B.Vandiver et al. Pittsburgh: Materials Research Society. 305–24.

Mecklenburg, M. F.1988. The effects of atmospheric moisture on the mechanical properties of collagen under equilibrium conditions. AIC Preprints. American Institute for Conservation 16th Annual Meeting, New Orleans. Washington, D.C.: AIC. 231–44.

Michalski, S.1993. Relative humidity: A discussion of correct/incorrect values. ICOM Committee for Conservation preprints, 10th Triennial Meeting, Washington, D.C.: Paris: ICOM. 624–29.

Reedy, T. J. and C. L.Reedy. 1992. Principles of experimental design for art conservation research. Marina del Rey, Calif.: Getty Conservation Institute.

Rijksdijk, J. F., and P. B.Laming. 1994. Physical and related properties of 145 timbers: Information for practice. Dordrecht, The Netherlands: Kluwer Academic Publishers Group.

Strang, T. J.K. 1995. A brief guide to thermal and controlled atmosphere treatments for insect eradication. Preventive Conservation1:4–5.

Strang, T. J. K.1995. The effect of thermal methods of pest control on museum collections. Proceedings of the Third International Conference on Biodeterioration of Cultural Property, Bangkok, Thailand. Bangkok: Thammasat University Press. 334–53.

Toishi, K., and T.Gotoh. 1994. A note on the movement of moisture between the components in a sealed package. Studies in Conservation34(4):265–71.

Waller, R.1992. Temperature and humidity-sensitive mineralogical and petrological specimens. In The care and conservation of geological material: Minerals, rocks, meteorites, and lunar finds, ed. F. M.Howie. Guildford, U. K.: Butterworth-Heinemann. 25–50.

White, B. S.1991. The influence of humidity on corrosion rate. Corrosion Prevention and Control. 39(6):154–56.

Wilkinson, R. S.1980. Further observations on freezing insects for storage. Entomologist’s Record and Journal of Variation92(11–12): 273–74.

Williams, M. A.1987. Furniture deterioration: Temperature and relative humidity. Antique Review13(2):17–20.


Conference Review for AIC 2004 in ICOM-CC ethno newsletter

March 16, 2009

http://www.icom-cc.org/ul/cms/fck-uploaded/documents/ICOM-CC%20Ethno%20WG%20Newsletter%2025.pdf

Conference Review AIC 23rd Annual Meeting Portland, Oregon June 9-14, 2004.

By Ellen Carrlee and Scott Carrlee

There were many talks of interest to ethnographic conservators at the 23rd Annual AIC meeting in Portland, Oregon, June 9-14, 2004. The theme of the conference was the Art of Cleaning: Ethics, Aesthetics, and Philosophy. The antagonistic speech from keynote speaker James Beck of Art Watch and the even more aggressive rebuttal from Kirby Talley Jr. focused on paintings conservation and emphasized issues of making assumptions, outside collaboration, original condition, and invasive treatments that have been central to ethnographic conservation for some time. The general session began with a talk by Landis Smith about the complexities of cleaning surfaces of Pueblo pottery. Loaded with useful technical details, this presentation emphasized the importance of combining documentation, ethnographic accounts and insights by curators and potters to make a decision regarding cleaning, noting that how a vessel should look is a moving target that changes with time and the viewer. Generally, there is a consensus that pots made as Western art can be cleaned to a higher degree than utilitarian wares. The type of clays and pigments used, firing conditions, surface finishing, “lime popping,” the impact of use on wear patterns and residues, coatings applied by potters and dealers, and old cleaning and repair methods for Pueblo pottery and are discussed in detail. Theresa Heady spoke about the ethics of working in the field and dealing with indigenous objects with cultural sensitivity. Her work at two Buddhist temples in Mongolia attempted to introduce our conservation values while respecting traditional practices that included resident artists re-painting old works, feeding resident birds as a religious ritual, and continuing replacement of old images with new ones. Students from the University of Mongolia were recruited to help with condition reporting. Deborah Bede presented the work of Mary Brooks and Dinah Eastop, “Matter Out of Place: Analyzing Conceptual Shifts in Preservation Values.” The core of the paper involved four models of dirt: “domestic” (related to household,) “Sacred” (such as relics,) “Art Historical” (particularly for authenticity,) and “Evidential” (including historical, forensic and legal significance.) Items with social ambiguity can be of greater interest, and the difference between soiled and clean object can impact its social significance. Virginia Green discussed the decision making process in her lab for determining if an artifact has museum dirt or ethnographic dirt and some successful cases of reducing soiling. Her experience with the Hopi, for example, included the concept that history is unified and there was not a distinction between pre- and post-collection dirt. This led to an unexpected opportunity to save time in treatment. Other groups felt it disrespectful to the maker to display an object in less than perfect condition. Green found covering cotton swabs with crepeline for cleaning wood with ethanol kept cotton fiber out of the wood. She urged caution when cleaning opaque vs translucent beads, since the inaccessible dirt inside translucent beads can make them appear gray after cleaning in contrast to the easier-to-clean opaque beads. Feather cleaning with non-ionic detergent and water followed by blow drying gave a nice appearance, but resulted in minor loss of barbs near the bottom of plumose feathers. The objects session began with fascinating research from Amber Tarnowski, Chris McNamara, Kristen Bearce and Ralph Mitchell about the nature of sticky microbes and dust on objects in historic houses. In this study, microbial populations were surprisingly greater indoors than they were in the soil outdoors. They feed on dust itself, with hydrocarbons from smog and pollution as sources of food as well. Most microorganisms are bacteria that produce a biofilm of exopolymers (mainly polysaccharides, proteins, and nucleic acids) that form a sticky film. This can make dust adhere to surfaces and becomes the food source for additional biological growth such as mold and fungus. Experiments testing effective methods of removal are now underway. Sara Moy presented her research on the potential of Groom/Stick to deposit residues. The product is more likely to leave residues of titanium dioxide and silicone when it is aged or used at elevated temperatures. Using soiled Groom/Stick to take advantage of reduced tack is discouraged because it can transfer contaminants. Instead, reduced tack should be achieved from lower temperature. Storing Groom/Stick in the refrigerator reduces tack and also prolongs its useful life. Stephen Koob gave a thorough review of why and how to clean glass from ancient to modern. He prefers Triton soaps 15:1 with a rinse in deionized or distilled water. Almost all glass can benefit from one good Museum cleaning during its lifetime, even crizzled glass, since washing removes the surface alkalis that can dissolve silica and free up more alkali over time. To extrapolate Steve’s information to bead disease, it would prolong the life of the bead to clean the alkali from its surface. Joanna Minderop, Cheryl Podisiki, and Ruth Norton offered their reflections about deinstalling and cleaning the 1950′s ethnographic and archaeological galleries at the Field Museum. Mounting methods were documented before deinstallation. Only 5% of 460 objects tested for arsenic were positive. Removing problem mounts from artifacts included the use of acetone poultices and vapor chambers to swell or dissolve adhesives. Wooden dowels were sometimes inserted into holes drilled into artifacts. These were removed by breaking the dowel flush with the surface, pricking a pilot hole with an awl, and drilling out most of the wood, followed by soaking the hole with acetone to facilitate picking out the remaining wood and adhesive bits. The wooden artifacts session included at talk by Alan Levitan about preserving large wood artifacts that do not fit in cases but are not architectural. Desert climates pose risk from erosion by windblown particles and exposure to sunlight. Fluctuations in temperature and RH can cause popping of nails and loosening of joints. Carpenter ants like fungally rotted wood, and termites can be found up to the border of Southeast Alaska. Generally, insects are the most severe problem in the Southeastern US. The fermosid termite is a new threat because it does not need to return to the soil on a daily basis as do our more common termites. In very cold zones, snow loading is a danger, but even painted surfaces can be preserved for 70 years or more. Sodium borates are an excellent line of defense against fungi and insects. They are water soluble, however, and leech out over time, even faster with soil contact. Softwood tends to decay from the inside out, and in one example of a large decayed interior cavity, mixing a foaming agent with the detergent helped to fully wet the surfaces. For repairs, Poly vinyl butyrols (PVB’s) are useful indoors for good penetration and better reversibility than epoxies. Used 1:1 in alcohol, PVB is a good adhesive. For exterior use, epoxies hold up better but have limited reversibility and penetration. The latter can lead to an “eggshell” effect where a surface layer is hardened and brittle with soft, untreated material below. Wooden or acrylic cradles help store and preserve oversize wooden items. Francesca Esmay and Roger Griffith contributed insights about cleaning methods for untreated wood. Although they were talking about plywood used by Donald Judd, it was interesting to hear how wet cleaning changed the color of the wood and could raise the grain. Dry cleaning by moving a blanket of crumbs along the grain with a large bristle brush or the use of a French polish rubber followed by vacuuming were preferred dry cleaning methods. Evaluation in the force of the rubbing revealed huge differences in personal style between conservators during treatment. Spectrophotometry showed a slight decrease in surface reflectance on some test panels after cleaning, but no drastic visible change. The buzz during the coffee breaks included a debate whether or not the approval of a curator was carte blanche to proceed with cleaning. Another topic was the possibility that the practice of making a sharp distinction between cleaned and uncleaned areas for the purposes of a DT photograph may leave a “cleaning line” after treatment. In the exhibitor’s area, a new product called “dry-gel” shows promise for both dessication and humidification procedures. The active ingredient is a corn starch based polymer that may be able to absorb more than 50 times it won weight in water, becoming a gel in the process. It is packaged in various sized paper packets. Artifex Equipment Inc is developing this product in conjunction with the National Agricultural Library of the USDA for use in book and paper conservation, but creative applications in ethnographic conservation may include humidification and disaster recovery.


Follow

Get every new post delivered to your Inbox.

Join 90 other followers