Pondering the Cleaning of Ethnographic Gutskin

June 12, 2010

Internal organ skins of marine mammals continues to be an area I find interesting and under-explored in the conservation literature.  Not long ago, several gutskin items came into the collection at the Alaska State Museum: two gutskin bags and one round hat.  The size of the skin strips and their physical appearance resembled materials often identified on artifacts as seal intestine.

Alaska State Museum 2008-10-1

The underside of the hat, both images are before treatment

The hat was recognized by the curator, Steve Henrikson, as quite special.  While made of traditional Alaska Native materials, it was a design typically seen in sailor’s caps such as those used by Russian and European seafarers.  Several hats of this kind can be found in one of my FAVORITE books, The Etholén Collection, which has many wonderful photos and descriptions of Alaskan artifacts in the National Museum of Finland.  The hats similar to this one are attributed to the Aleut.  Our hat had dyed wool tufts and remnants of feathers, as well as red and blue paint on the welting sewn into the seams.

The hat was among recent acquisitions selected for the summer 2010 Alaska State Museum exhibition “From Gift to Gallery.”  I recalled that in fall 2009, our intern Lauren Horelick noted that humidifying seemed to help release dirt.  She observed this during treatment of a pair of Aleut or Alutiiq boots made from a marine mammal internal organ tissue, possibly sea lion esophagus.  

Lauren Horelick working on boots from the Sheldon Jackson Museum collection, 2008-6-1

Lauren wrote in her report,  “After exhausting dry cleaning methods, aqueous cleaning began experimentally with distilled water on cotton swabs. Initially this did not appear to be an effective method, producing very minimal soiling on the swab. Perhaps this was due to a lack of applied pressure. However, after the boots were humidified (step 6) the use of a cotton swab and distilled water removed a significant amount of dirt. A 16-ounce can was eventually filled with completely blackened swabs after both boots were surface cleaned along the interior and exterior.  It is possible that the process of humidification swelled and loosened the dirt from the surface of the legging material. Humidity may have also relaxed the fibers sufficiently to release the soiling. The cleaning appeared to bring a more luminous quality to the boots with an overall brighter yellow color.”

Lauren manipulating the skin of the boot

After surface cleaning the hat with dry techniques, we undertook overall humidification of the hat in a humidity chamber.  I brought the chamber up to its practical limit of about 80% RH over the course of about four hours.  The method I like to use involves small containers of water with sponges in them to increase surface area, and after a couple of hours I soak a few strips of crumpled acid-free blotter with water and add those to the chamber to speed up the rate that the humidity increases.  The wet items are located below the wire shelf, so cannot come in contact with the object.  I need the object to get pliable, manipulate it and position it within the course of a single work day because I don’t want to leave gut material damp overnight.  The cotton textile lining got very limp, almost damp.  But the gut was not cooperative for very long, and I had a very short working time.  Maybe 10 minutes maximum before it was too stiff to manipulate without risk of new tears.  I wondered if I should have used some solvent for humidification, as sometimes the smaller molecule size of certain solvents is thought to penetrate better during humidification, but I was concerned about the pigments. 

Gutskin hat beginning humidification in the chamber

I inverted the hat and used small clips suspended from a hoop to encourage the rim back into shape.  The wooden clothespins were attached at intervals around the rim over small sections of curved (by curling) blotter paper on the interior and exterior of the rim.  Because the gut started to become brittle again, this was the extent of the re-shaping at the first pass.

First attempt to reshape the rim of the hat

A second overall humidification was repeated in the humidity chamber, following a similar humidification profile.  Put in at 8:30am and removed at 3:30pm, as the rim began to collapse again and take on memory of crumpled shape.  Stuffed out the outer areas of the hat with acid free tissue and inserted a cotton-covered disc of 1” polyethylene foam inside rim to help maintain shape.  The foam was cut smaller than the rim to leave space for strips of curled blotter to be clipped both inside and outside the rim again.  The foam was then placed on a riser so the clips could hang free and their weight could help encourage the rim into position.  A little extra weight was added to one side in order to even out the shape.  I did this with magnets attached to the springs of a few of the clothespins.

Reshaping the hat before wet cleaning

Now comes the interesting part, and I was grateful for the assistance and observations of Aurora Lang during this phase of treatment.  Aurora has a Museums Studies master’s degree, and was volunteering at the museum for a few months before she became the new Curator of Collections and Exhibits at the Cordova Historical Museum.  She and I agreed on our observations about the wet cleaning of gutskin. 

Some of this dirt had come off with a soft brush and a low-suction vacuum, but much still remained on the surface after dry cleaning techniques were done

The sooty dirt was not removed nearly as well with distilled water as it was with saliva.  Warm water works better than room temperature water, but not better than saliva (which also affords more control.)  On a scale of one-to-ten, with 10 being the best, the use of saliva is a 10, warm water is a 7 and cold water is a 3.  Warm water is at least twice as effective as cold water.  Saliva aids in the release of the soot, and repeated rubbing of the area is not needed as extensively it is with water alone.  Swab slides over the surface easier, and it feels a little more lubricated.  When water is used, the rubbing makes crinklier sounds and feels more aggressive.  Biologically, saliva and gut are quite compatible.  To what degree are we benefitting from enzymatic action?  Should we be worried about putting a bit of our own DNA on the surface? 

Lower left area is cleaned, the horizontal area has not yet been cleaned in this image

 Dirt continues to be released with repeated applications of saliva.  The best cleaning happens if you take two steps forward and one step back.  It seems that if you get the gut in one area to seem clean, and then you move on to another area and let the first one dry, more dirt comes to the surface in the first area, showing up as little islands of dirt in the crevices.  Cleaning a small area (approximately 2” x 1”) will take about 3-4 minutes on the first pass, and only about half that amount of time on the second pass which is most effective if done perhaps 2-4 minutes later.  This can be repeated a few times until the swab no longer comes away dirty.  On the first pass, the gut will get very pliable and soft, like pasta or perhaps like seaweed in miso soup.  The texture is delicate and it seems as if it might be punctured easily but we did not have that problem.  On the second pass, perhaps 4 minutes later, the gut feels supple under the swab but not pasta-like as on the first pass.  It is not crinkly and is still semi-humid.  It is in this state that a lot of dirt can be removed from the gut.  After cleaning, the gut has a semi-translucent luminous quality, almost glowing, that it did not have before cleaning.  Feathers and pigments were avoided.  Because we were concerned with the residues of the saliva cleaning, we went over all those areas one last time with cotton swabs dampened in ethanol.

From left-to-right: cleaned with saliva, distilled water, and warm distilled water

For comparison, cleaning was also attempted on the lined gut bag that was also part of this accession.  Since its construction and materials were similar and it came from the same accession, it is assumed that its manufacture and soiling history would be similar.  It was notably more difficult to remove dirt from the un-humidified bag, but cleaning could be done successfully with repeated passes.  More passes were required and dirt did not come off as easily.  From this we felt that perhaps Lauren was right and that our overall humidification of the gut made it easier to clean.

After treatment, top of hat

After treatment, gutskin hat, Alaska State Museum collection 2008-10-1

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WOAM 2010 in Greenville: Extracurriculars

June 2, 2010

Arrived in the fried-chicken-scented Raleigh airport at 11pm with 100 miles to drive…speed limit is 70 here!  Staying at the dorms on the Eastern Carolina University campus at the crazy good price of $38 per night including breakfast.  I was very lucky to attend this conference thanks to grant funding from the Rasmuson foundation in Alaska (www.ramuson.org).  Personally I really like it when conferences trap attendees at the same location.  From what I can tell, the conference organizers have mainly been Sarah Watkins-Kenney of the North Carolina Dept of Cultural Resources, Emily Williams from Colonial Williamsburg, and Kristiane Straetkvern from the National Museum of Denmark.  Usually, when I come to a conference all the way from Alaska, that seems kind of a long way.  But this conference has more than 80 people from at least 15 different countries, and I am sure the folks coming from Australia had to wake up earlier than I did.  I’ve been told this would be an intimate, open and welcoming group.  I am equal parts thrilled and terrified to be among the people who can actually converse with me about polyethylene glycol.  I hope they will be gentle when I reveal my ignorance, but I am willing to get humiliated a little bit if it would mean getting my facts straight.  There will be some 43 papers and 13 posters in the next four days.  The conference proceedings will be dedicated to Kate Hunter, who passed away in January and is perhaps best known for her masterful work on the Newport Ship project.

 QAR BBQ May 25,2010

Brunswick Stew, Cornbread Sticks, Eastern NC Style BBQ (basted with a vinegar sauce, pepper, a little bit of tomato), coleslaw in a 5-gallon bucket.

 The tour of the QAR was terrific and I could have spent hours there, really.  I am sorry that this is the picture I have for you, it would have been much more spectacular had I been able to get an image of Jim Spriggs dressed up like a pirate, complete with inflatible parrot on his shoulder.

Thursday Evening Dinner Reception

Richard Lawrence gave a talk about the past 40 years of underwater archaeology in North Carolina.  He was the director of Underwater Archaeology for the Department of Cultural Resources for 29 years, and is just about to retire.  North Carolina has some 300 miles of coastline, including features I cannot precisely define like capes, sounds, and shoals and such.  Apparently, Cape Hatteras is a vulnerable point that sticks out into the Atlantic and the northbound Gulf Stream Current goes within 15-20 miles of it, closer than anywhere else in North America.  And that’s also where it meets the Laborador current going south.  Yikes!  There are some 5,000 historical and documented wrecks along the NC coast.  The discovery in 1962 of a civil war blockade runner (the Modern Grace who sunk in 1982) was the first wreck they dealt with, and enthusiasm about the Civil War Centennial helped get the Fort Fisher Preservation Lab built the following year. Leslie Bright, “more of a chef than a chemist”, and armed with Plenderleith did most of the conservation work on the artifacts 1964-1998.  The Underwater Archaeology Law was enacted in 1967 to help put artifacts under state ownership.  For a while there were sport/hobby permits and people were allowed to keep stuff they found if they declared it and it wasn’t deemed especially significant.  In 1972, Gordon Watts became the first underwater archaeologist there.  In 1973, the USS Monitor was found and research on that was ongoing till 1984.  The first national marine sanctuary was established, and NOAA contracted them to manage and do research.  There were UNC field schools from 1974-1979 and ECU field schools 1979-1982.  Gordon Watts and maritime historian Bill Still went on to found the ECU program in 1981, and things moved towards being more program oriented and less project oriented.  Many more wrecks were dealt with, and then there was an interesting tagging program for wrecks, so if they moved around they could still be identified as something that was known.  In the mid 1980’s some 24 very old dugout canoes were found (Middle Woodland Period, more than 4000 years ago) when drought and firefighting activities lowered the water level in Lake Phelps.  This was one of the pre-conference tours for WOAM (I missed it) and apparently it was most enjoyable, even when some conference delegates became a bit, er, waterlogged themselves.  In 1991 the wreck of the USS Huron (from 1877) became the state’s first and only underwater wreck.  The Queen Anne’s Revenge Project (QAR) got going in 1996 and because of the continuing exposure of the wreck, it will be a full recovery.  They are about halfway through, but funding lately has been poor.  The goal is to have everything recovered by 2013, and a museum by 2018, the 300th anniversary.  In September of 2008, the state’s oldest shipwreck was found.  Thought to be from the 1650’s (coin from 1642 and spoons from 1620) it was on the beach and moved around quite a bit before it was hauled further up on shore and there is just no money for it right now.  In hearing all this history, I wondered two things: 1) what info and experience is there in North Carolina that could help with the establishment of a maritime society in Alaska? And 2) there is a name strongly associated with conservation of marine archaeology in North Carolina that is conspicuously absent from the official discussions at the WOAM meeting.

Check out additional posts on the business meeting, specific WOAM personalities, the flavor of WOAM, and Lars Andersen’s advice to me on freeze drying at the AIC’s news blog.


WOAM 2010 in Greenville May 28

June 2, 2010

ANALYSIS AND CONSERVATION OF LEATHER, BONE, AND OTHER ORGANIC MATERIALS

A New Approach to Excavating and Handling Waterlogged Textiles from the American Civil War Submarine the H.L. Hunley. (peer reviewed)

Johanna Rivera and Philippe de Vivies

The Hunley was the worlds’ first successful submarine, sunk in 1984 and found in 1995.  Over 1,400 artifacts have been recovered steadily since 2005, including textiles and organics (wood, leather, rope, horn).  The inside of the submarine was completely filled with sediment.  All crew were found at their stations.  The talk involved the textiles on Lt George Dixon, removed in 7 block lifts.  The block is placed in a tank and then slowly filled with water.  A syringe filled with water is used to dislodge the sediment.  Sediments are vacuumed off with a siphon hose made of PVC plastic, controlled by pinching with the fingers.  When the need comes to flip it, they fill in gaps with foam, then cover all with a thin plastic film, and then fiberglass (DuraPower Inc Pipe and Hose Repair Kit) and then polyurethane resin.  When firm, then they can slide something underneath and flip, exposing the other side for cleaning.  Four fabrics were found: a fine black or brown wool, a cotton/wool, a red that turned brown with exposure to UV light, and a strange thread that was all that remained of suspenders that were apparently made of natural latex rubber.  Fragments of textile were unfolded underwater, and rounded Mylar patches helped with the manipulation.  One textile was a vest, but its stitches that held in the lining were only on the surface, no longer penetrating through the cloth.  There is an entire AIC presentation on the vest treatment.  Use of a surfactant helped remove dirt from the textile and keep it in solution instead of re-depositing on the textile.  There are five more blocks from Dixon to be dealt with, and another 27 textile blocks from the rest of the ship, a huge undertaking.  Elizabeth Peacock asks about dye analysis, and says its not likely to be madder, for example, as madder dyed textiles are often better preserved than other textiles in the burial environment. 

A Neolithic Shoe from Sipplingen Conservation and Technological Examination

Ingrid Wiesner

The shoe was found in a burned layer, and thought to be 5000 years old.  The material seems to be strips of retted bast fiber, from the lime tree (tilia?)  Comparisons were made to other old shoes that had been treated: Feldtkeller (1989) used PEG 400, and consolidated with Luviskol K30 after and then Bojesen-Koefoed et al (1993) using high molecular weight PEG.  Seems that for this Sipplingen shoe, 8% PEG 1500 followed by freeze drying was the way to go.  Another example about how the conservation field is moving away from the use of low molecular weight PEGs.

Analysis of Plant Fiber Artifacts from a Shipwreck: Application of Material History Methodology

Runying Chen

Dr. Chen had a cool chart that was looking at Observation Data, Complementary Data, Supplementary Data, and then Conclusions along the rows, and then the columns were looking at Material, Construction, Function, Provincial, and Value.  This was Smith’s Material History Methodology from 1985.  Fits nicely with conservation treatment report format, doesn’t it?  Dr. Chen was saying it really helps you to be more disciplined and eliminates pre-conceived notions or bias by using a matrix like this.  There’s a recent article in the Journal of Nautical Archaeology that is a cordage study (French?) and has a new recommended framework for how to describe cordage.  It is tricky to compare cordage if people are not talking about it in the same way.  Louis Bartos is a sail maker and historian who was a useful resource.  Info about the plant fibers can give you an idea about the size of a ship and the kind of sails it has…looking at the angle of twist, type of weave, seam construction, stitching, etc.  I think Dr. Chen felt a little out of place in the context of the other papers, but I thought this was really valuable.  With our noses so deep in the science, it is nice to be reminded of the balance we need to have with the interpretation of our wet organics and not just the preservation of our wet organics.  Conservators are often called upon to help interpret what we are seeing and it is great to be reminded of some of the work that is happening in that area too.  And knowing what people need to look at for interpretation helps guide the aspects of what we need to prioritize for preservation.

 

Polyethylene Glycol Treatments for Basketry on the Northwest Coast of North America (peer reviewed)

Ellen Carrlee and Dana K. Senge

This was our talk, and I was so glad it was on Friday so I had a chance to ask a lot of people about it before getting up in front of everyone.  Despite feeling a little out of our element, Dana and I were definitely on the right track.  We were trying to come up with a PEG protocol that would work for basketry.  I had two baskets in the lab already treated with 20% PEG 400 and 5% PEG 4000, based on the best knowledge from the late 1990’s, and even though they looked nice, they were too fragile.  So I wanted to see if using high molecular weight PEG would help, maybe without low molecular weight, and maybe at higher concentrations.  I think that panned out, and is in harmony with the current understanding.  Also, my consolidation with Butvar B-98 seems to be something others have found useful.  Maybe 55% PEG 3350 is a good way to deal with very deteriorated spruce root.  And maybe basketry treatment, which has been very challenging for lots of people, might be best approached with a two-step treatment: step one being PEG and step two being consolidation.  I did not get an answer about why my unheated sample treated with 20% PEG 400 and 75 PEG 3350 turned very dark on cycling RH but the heated sample did not get dark.  In all cases of treatment with 75%, that was too high and they were excessively brittle.  at Dana’s work in compiling old basketry treatment info is right on the money as well, as this kind of data is really useful and she was right to start capturing that, too.  We are still missing a bit of the degree of deterioration problem, since Dana and I struggled with what we were seeing under the microscope.  I now have this fantasy that I can attract a grad student in wood anatomy to come from Minnesota and work up spruce root and cedar bark for me.  If we cover those two materials, we’ve covered most of the baskets on the Northwest Coast?  Carlos is keen to try silicone oil on the problem, and maybe I will collaborate with him a bit on that.  I have to think it through, since I am feeling like I have a good direction to go with these treatments using techniques that I am comfortable with in terms of reversibility/retreatability, but the idea that giving over a bit of this material for silicone oil might add to our overall big picture knowledge of various tools in our toolbox…hmmm.  Tara Grant agreed that POLYOX wasn’t that useful, but in order to work with it they found that putting a pool of it on the table and pushing to object into it was a good way to deal with its lousy handling properties.  Kate Singley reports she’s had good luck with Lascaux, although the kinds I tried didn’t work so well for me.  Rope gives a similar problem, and was reported on at the Portland WOAM.  In Denmark, they tried using Paraloid F-10 on brittle rope after it was PEG treated and that worked well for them.  For the consolidation issue, I guess it matters quite a bit whether your consolidant is dealing with the PEG or dealing with the wood.  I suspect that if it is the former, then solvent-based consolidants are going to be good (as I was finding) but for the latter when wood is available for bonding (perhaps if the PEG has been cleaned off the surface) maybe that is when people are getting better results with the water-based consolidants.  And one final revelation, Dana points out that historical spruce root baskets are BRITTLE too!  Chemist Mikkel Christensen from Norway points out to me during one of the breaks that a general rule of thumb is that you can have stability or you can have flexibility but you cannot have both. Don’t miss Dana’s weblog of past basketry treatments and their outcomes at http://waterloggedbasketry.blogspot.com

Assessing the Physical Condition of Waterlogged Archaeological Leather (peer reviewed)

Katerina Malea, Thelxiopi Vogiatzi, David E. Watkinson

To ID the animal species, they used SEM to look at the hair follicle pattern.  To assess degree of deterioration they were looking at amino acid analysis of the collagen.  In examining leather visually, people tend not to agree in how deteriorated they think it is.  pH reflects degree of hydrolytic deterioration.  In the 4.6-7.5 range, with most in 5-7 range.  They were also looking at shrinkage temperature, and how broad the range was from when the first one went to the last one in heating for shrinkage.  Looking at ratio of basic:acidic amino acids?  If the ration is low, does that indicate oxidative deterioration?  I am not quite catching all the science, it is a little above my head on this talk.  Some commentary afterwards cautioned the use of shrinkage temperature as a tool, since it was designed for use on recent leather.  Apparently, there’s been some difficulty using it on archaeological leather because of mineralization?  It behaves unpredictably?  There was a 1997 study that showed a correlation between mineral content and shrinkage temperature.  The plot thickens!!

A Comparative Study of Various Impregnation and Drying Methods for Waterlogged Archaeological Leather

Angela Karsten, Kelly Domoney, Liz Goodman, and Helen Ganiaris

There’s a backlog of leather to be treated in the UK, which is a problem because it is prone to mold growth, analysis cannot be completed until it is dry, and it cannot go into a repository wet.  Usually, leather from anaerobic terrestrial sites is pre treated with glycerol or PEG and then freeze dried.  20% glycerol gave the best results, and EDTA along with it was good and also helped with flexibility.  Using that in conjunction with vacuum freeze drying was the best, and air drying was OK too.  All treatments dried darker and somewhat brittle, although the freeze dried ones were easier to examine without damage.  The ones that went through controlled air drying with a series of salts to control RH had challenges with mold and using the technique was a pain.  If they got some pre-treatment, even 10 years in storage was OK and they didn’t get moldy and good results were still possible.  However, without pre treatment they tended to curl up.  Ian Godfrey reports that in Australia, they found the glycerol treatments caused dessication and brittleness over time.  In the UK, however, it seems that they’ve been using it since the 80’s without that issue, although that’s anecdotal and maybe it needs to be looked into.  Dr Godfrey is keen to assist in the analysis of leather and help distribute the results.  I think this issue of glycerol is really interesting.  Like how the glycerol in the alum treatments for wood seemed to make them much worse?  What is up with glycerol?  I want to understand it better.  Jim Spriggs says they treated leather in York with glycerol and freeze drying since the 1970’s and it does change over time.  The ones in York that came out the best were some weird combo of solvent dehydration and then a solvent soluble oil?  Wow.

Efficiency and Quality in a Batch Treatment: the Conservation of Over A Hundred Leather Shoes and Fragments

Jessica LaFrance

Metal cistern from 1850-1870 contained lots of leather shoes.  Used an ultrasonic dental scaler to clean.  Removed chlorides in tapwater baths, agitated, up to 3 months long.  Iron was removed with either 2% dibasic ammonium citrate as a batch of 50 (immersing them twice) or 5% sodium dithionite in 2% EDA (did I write that down correctly?) used on shoes individually.  The latter worked better, but cost more, took longer to prepare, and required ventilation.  Iron stains might have helped preserve the collagen?  The monitored the color of the solution to know when it was done.  When it was rinsing clear, then they treated the leather with PEG, 20% with 1% Hostacor IT since there were metal attachments and wood inserts inside the shoes.  She reshaped with foam supports and Supercrinx stretchy self-adhering bandages, and freeze dried for 2 weeks.  There was 7-10% shrinkage, and really maybe even a little more than that since they likely shunk a bit in transit.  After freeze drying, used some 2% Klucel G in ethanol where needed, and used Lascaux 50:50 498HV to 360HV applied by brush to sheets of Reemay and reactivated with acetone for tear repair. Susanne Grieve mentioned that the Hunley shoes were preserved with commercial shoe inserts successfully.  She also likes a material called Bibac plastic, which can be shaped with a hairdryer.  Sounds like it has lots of holes in it, so there is less surface area and the leather dries better?  Susanne likes Teflon tape during PEG treatment because organic bandages like traditional roller gauze has gotten moldy or has left marks on the surface of artifacts.  Emily Williams jumps into the issue of how the term “batch treatment” affects the concept of the artifact value to curators and collection managers.  Objects treated individually are perceived as being more precious.  But is it chicken and egg?  Have the curators and collections managers already made that judgment before the batch treating happened?  In the UK at least, with the volume of material and the limits on resources available to deal with it, there is a risk that things might get discarded rather than treated if batch treatment was not an option.  With some 35 years of experience, Elizabeth Peacock wisely says we don’t have to advertise that batch treatment is how it is done!

Conservation of Thule Skin Clothing from the Sannirajaq Site, Nunavut

Tara Grant

For me, this was maybe the most exciting talk of the conference.  Tara does archaeological fieldwork as well as conservation work in the CCI lab.  A 2006-2007 excavation of houses from 100-1400AD brought up boots, belts, fur parkas, bird skin inner parkas, gutskin anoraks, pants etc as well as human remains of 8 individuals.  After consultation, it was determined to rebury the human remains, and the clothing was excavated separately.  There were health problems and strong odors to be dealt with.  The precendent of Christchurch, Spitalfelds, England was useful.  It seem that lead dust, mold, and parasite eggs are a bigger risk than infectious disease.  Anthrax and smallpox can survive, but plague, cholera, typhoid and tuberculosis do not tend to survive in burial.  The site was pre-European contact and there were no domesticated animals.  The Canadian Science Center for Human and Animal Health was also helpful, and determined that with appropriate personal protective equipment, the staff would be OK.  They used a HEPA unit and charcoal filter for odors, mostly from putrescine and cadaverine.  These are water soluble compounds that smell even more in high RH conditions.  Mary Ballard’s work on this was very helpful.  20g/L water of sodium bicarbonate for proteins and sodium carbonate for cellulosics.  The objects she was talking about were mainly a parka with seal fur, caribou fur and birdskins with the feathers still on them.  (Cool tidbit, diving birds have stronger skins!)  There were also boots of defurred seal skin.  Gutskin anorak.  They were dealing with hair loss, slippage, dirt, fat, loose/open seams, rips/holes in the skin.  Some of the loss or damage was from pre-burial, as evidenced by things like a knot tied in the gutskin near a loss.  Tara had really cool slides about gutskin structure.  Summer gut is dried in above-freezing temperatures and is not as flexible as winter tanned gut which is dried at below freezing temperatures.  They were looking at shrinkage temperature, which as between 45 and 63 for the artifacts, and modern seal and cow are 55C and 60C respectively.  There’s a new technique for measuring Ts which is more accurate than the old visual method, so the reference numbers are a little different these days.  So on the anorak, for example… They were using 20g/L of sodium bicarbonate, and is thought to preferentially react with amine rather than protein. 30 minutes, agitate, pH of 8 (a little high for skins) and then sodium dodecyl sulphase 0.5w/v as an anionic detergent to remove fats.  Brush and cavitron cleaning, then a 17 hour rinse with running water to remove detergent.  Repeated detergent and deodorizing, then rinsed for 4 days.  They used 20%v/v PEG 400 for 24 hours, and the rinse, tamp, reshape, freeze at -22C.  Odor removal was only partly successful.  Feathers especially still had some smell, but seams were loosening and feathers were starting to detach so things had to stop.  AT the gut didn’t smell at all, and they were able to use a cold mister and finger pressure to manipulate and then clamp into the desired shape. 

Conservation of Waterlogged Ivory

Ian Godfrey and C. Wayne Smith

This particular talk was dedicated to the late Sophie Lussier, who did some important work on testing materials to use with ivory.  Elephant tusks were found in a 1970’s excavation of a Dutch shipwreck.  Tusks form as a cone-in-cone structure.  Tendency to delaminate.  No relationship between deterioration of ivory and success of treatment options.  Some tusks had been “looted” pre-ban and air dried OK, others did not air dry OK.  Layer of corrosion products on the outer surfaces were iron rich, and then there was an inorganic matrix better preserved at the core.  Calcium would be replaced by iron, and you’d see that lovely blue vivianite.  FTIR was the most helpful tool, it is really good for bone and ivory.   There was collagen in the rich outer layers, but not in the core.  Texture of the ivory was different throughout as well, with some areas as soft as paste and others very hard.  Form 1996-99 they tested Rhoplex AC-235 30% for 4 months, Primal MV-23-LO 30% for 4 months, Gelatine 30% at 30-40C for 4 months, Biodur S-10 with S3 hardener and S6 gas cure (plastination) and finally silicone oil (SFD-10 silicone oil with MTMS crosslinker and the dibutyltindiacetate catalyst.)  The aqueous treatments were all slow dried over 15 months.  The Rhoplex penetrated only 1mm in.  Aqueous stuff didn’t really work so well.  Really, only the plastination and the silicone oil treatments worked.  To do the silicone oil, they bound the tusk so it would not fall into pieces during treatment.  For the plastination, they probably ought to have done it at -30C in acetone, but it was done at room temperature in the hopes it would remain more fluid and penetrate better, and so the results maybe not as good as they could have been.  They embedded the tusk samples in epoxy and polished it down to look in SEM and see where the material went.  There was lots of silicone oil in area with heavy degradation, and then a steady amount in other areas.  By making a mixed sample with non-silicone treated ivory, they were able to prove they were not just smearing silicone around during polishing.  People were wondering after the talk if the silicone oil treatment would inhibit the oxidation of the pyrite.  Looked from this talk like silicone oil might be an appropriate tool for treating this tusk material since there wasn’t really anything else that worked.  At the end of his talk, Ian Godfrey brought down the house with killer images of live “flying” penguins from his work in Antarctica.  Is it an accident his talk was last?  Or was he intentionally chosen as the closer?

Check out additional posts on the business meeting, specific WOAM personalities, the flavor of WOAM, and Lars Andersen’s advice to me on freeze drying at the AIC’s news blog.


WOAM 2010 in Greenville May 27

June 2, 2010

SULFUR, IRON, ALUM, AND OTHER INORGANICS IN WOOD

Vasa—Recent Preservation Research

Lars Ivar Elding

The Swedish warship the Vasa sunk in 1628 and was recovered in 1961.  It is 900 tons, 60 meters long, full timbered with a 40-50cm hull and had 20,000 objects on it.  Since it was found, it has taken 50 tons and PEG and 15 tons of borates to preserve it, and maybe 5-10% of its current mass is PEG.  The 200kg pentachlorophenol it was treated with as a biocide has decayed over time and is no longer observable.  It went from having 150% water content down to only 10% today.  The ship gets some 1.1 million visitors every year.  In the 1990’s salt precipitates were discovered, made from sulfate salts reacting with the iron, causing an internal formation of sulfuric acid.   This was the subject of a 2002 paper in Nature, but now we know this was just one of several reactions and the situation is rather complicated.  From 2003-2006, the “Preserve the Vasa” project aimed to answer some questions: What was the microbial activity? (negligible) How about sulfur-iron chemistry?  Removal of the iron catalyst (EDHMA and DPTA dunno if I got those acronyms right though) PEG stability (formic acid found but decay in practice was negligible) Influence on the wood?  (Yet to be determined) The next phase, the 2008-2011 “Future for the Vasa” project, asks, Which processes are important? How extensive? How fast? How is the wood effected?  Lot of oxygen and a pH 4 is needed to keep reactions going.  There are low pH values deep in the timbers, so perhaps reactions are going on there?  The surface layer is weak and degraded, then there is an area which is rich in iron 3+ and then deep inside there is iron 2+.  Somehow, a high concentration of sulfur inhibits iron-dependent degradation.  Cellulose hydrolysis caused by sulfur is an over-simplification.  Because of all the visitors, they are limited in the kinds of techniques they can use.  In 2004, a new climate system was installed.  RH 55% and temp 20C.  Iron bolts are being changed out for carbon fiber or stainless steel.  The ammonia gas that might help only has 1-2cm penetration, look for a 2010 Studies in Conservation article about it.  Right now, we ought to take a sample and store it at low temperature and  low pressure and look for change over time.  Wish we had samples from 10 years ago, even though it does not look like there have been major changes in that time, who knows?

Iron Removal from Waterlogged Wood and the Effects on Wood Chemistry

Vicki Richards, Ian Godfrey, and Kale Kasi

Recovery in 1985 of an iron steam engine from the 1872 wreck of the SS Xanthro, had electrolysis in sodium hydroxide for years.  In 1994, the baseplate was removed and there were some 100 wood chocks under there, coated in tallow (a lubricant for the engine.)  From 1991-93 they treated them with dithionite and citrate and PEG 400 to preserve them and remove the iron.  Took some 20 days for the iron to start coming out, and it seemed to come out best with dithionite.  The solution got pretty acidic, below 3.  They tried diethylentriamine penta acetic acid, but it wasn’t as good.  Tallow interfered with the FTIR peaks when they tried to look at effects of chelating agents on the deterioration of the wood.  I have to admit, I didn’t understand this chemistry very well due to my own lack of background.

Nuclear Magnetic Resonance and Fourier Transform Infra-red Spectroscopic Analyses of Acid-Affected Waterlogged Archaeological Wood

Ian Godfrey, Vicki Richards, Lindsay Byrne, and Emil Ghisalberti

Trying to look at degradation of Vasa to reference wrecks still on the seabed to see what kind of deterioration happens after treatment compared to doing nothing and leaving it in situ.  Had to have big samples, 200mg, so there is sample left for other kinds of work also.  Seems like there was more cellulose loss from the Vasa, and the inner part has lost more than the outer part.  Perhaps areas that have more formic acid, like the outer areas, indicate more PEG since formic acid is a degradation product?   There was more acetic acid on the inner parts.  Truth is, there is more PEG degradation in the inner core even though there was more formic acid on the exterior.    This is another talk where I could not follow all the science very well, a little above my head.  I actually wrote in my notes at one point, “Big ol’ brain on Ian!”

The De-Acidification of Waterlogged Archaeological Mary Rose Timbers with Strontium Carbonate Nanoparticles.

Eleanor Schofield

The Mary Rose was the flagship of Henry VIII, dating to 1545.  About half survived in silt and was recovered in 1982.  Hoping to have money to rehouse it in 2012.  There are some 19,000 artifacts as well, and they have a sulfur problem.  They are using XANES (xray absorption near-edge structure spectroscopy) to see different oxidation states and distinguish between the sulfate compounds.  Before, sulfur was “spectroscopically silent.” SrCO3 good because strontium was a better marker when used at .005 molar, and it became associated with sulfur in the wood.  Forms SrSO4?  Stronium sulfate as an insoluble material, something more stable to leave in the wood?.  Gosh, this was pretty beyond my ability to grasp as well.  These heavy-science talks exceed my science knowledge, so I can’t interpret them very well.  Sorry about that.

Extraction of Sulfur Compounds from Archaeological Wood by Chemical Oxidation with Sodium Persulfate

Khoi Tran, Fanny Bauchaud and Clement Werner

Trying sodium persulfate to chemically oxidize the iron sulfides, 13.5% worked the best.  Buffered the acidic solution with sodium hydrogenocarbonate NaHCO3.  On the LaLomilla wreck, they were finding 80% pyrite, 20% silica and pyrite accretions, with 17% ash on the surface and 7% inside of the plank.  5 baths needed to soften accretion so it could be mechanically removed with a brush.  Only about 10g removed from a 6kg plank?  The PEG treated and freeze dried.  There were still minerals in there and PEG could not fully penetrate, so there was some shrinkage.  Also tried to do a poultice application on the crusts that came out after the PEG treatment.  Cellulose pulp, .14M sodium persulfate, and 0.05 sodium bicarbonate buffer.  10 months later, they still have pyrite but look OK with no effluorescence.  Maybe try electrophoresis in a poultice for in-depth extraction of ionic compounds? That has worked in the past to extract alum from wood. 

Re-Conservation of Wood from the Seventeeth Century Swedish Warship the Vasa with Alkoxysilanes: A Retreatment Pilot Study Applying Thermosetting Elastomers

Carlos Cabrera Tejedor

In my notes at this point, I have written the remark, “OMG, I am the least illustrious person in this room!”  Carlos was using Xiameter PMX-200 silicone fluid CAS # 70131-67-8, Dow Corning SDF-1 (about 75CST viscosity, ranges from 55-90) and the MTMS brand name Xiameter OFS-6070 silane CAS# 1185-55-3 as the crosslinker.  Carlos was looking at color using a Munsell color chart, texture, dimensional change, weight, volume variation and microscopic features.  His first test was to immerse the Vasa sample in MTMS at 70C to extract PEG over about 20 days, dry it, and catalyze the MTMS.  Was a little waxy, heavier, and maybe they could not get out the PEG enough?  Second test was soaking PEG out with deionized water, progressive removal of the water with ethanol and then to acetone in 25% increments, impregnating with a little vacuum to help get all the acetone out, cleaning, and then catalysis with DBTDA.  The evaluation was OK, except for the volume variation and the microscopic qualities.  However, in the third test he removed the PEG in water only, not just in one step with MTMS, and the results were much better.  A gallon of silicone oil is $160, and a pint of MTMS is $75.  So if I understand right, the alternate MTMS treatment is better than either the traditional one or the standard silicone oil treatment when re-treating PEGged wood from the Vasa.  PROS: short time to do it, not too complicated to perform, and means that minimum preventive conservation would be needed to curate the wood.  Thin layer of agent (a few microns) allows much of the woody quality to be retained and the morphological features to still be easily observed.  Treated wood is hydrophobic, chemically inert, resists acids and bases, and resists change with UV light.  CONS include non-reversible, non-re-treatable (only repeatable with same chemicals), price of reagents, and the health and fire hazard. 

I have to say I spent a lot of time talking with Carlos during the conference, and liked him very much.  He was personable, candid, competent, curious, enthusiastic and open-minded.  Before Carlos, silicone oil was firmly in the “do not trust it” pile of treatment options that I had no intention of considering.  Now that I have spent some time with Carlos, I feel like I have a much better understanding of the silicone oil issue.  For example, I had recently heard that while it is NOT reversible, it is “retreatable.”  Indeed, this term “retreatable” has gotten a lot of traction in the conservation world now, admitting that we are not ever going to get everything back out again safely, so “reversible” is in our the theoretical standards and ethics while “retreatable” is kind of the real-world version.  However, in chatting about it, Carlos now plans to use the word “REPEATABLE” with silicone oil treatment, because in fact you do not have any other retreatment options with other materials.  You can only repeat the original treatment to try to get better results.  And Carlos was very candid in saying that when you get good results from the silicone oil treatment, they are really beautiful.  To hear him talk, the results are almost seductively, unbelievably beautiful.  Only the trained hand could really say, “hmmm, this surface is maybe a little too silky…not quite exactly natural but damn close.” (my own quote) But when it goes bad, it goes really really bad and there is no way back.  Carlos’s term, “It is like a bulldozer.”  And then there is the issue of the lab where all the LaBelle items are being done.  Time will tell, but if the treatments hold up, that will be lovely, and if they don’t… well, the vast majority of all the organics from that ship, thousands and thousands of artifacts, have been treated since 1998 with this material.  When you have a hammer does everything look like a nail? 

Possible Uses of the Calcium Complex of EDTA to Remove Iron

Mags Felter and Anthony Crawshaw

Mammoth tusk needed iron removed in order to improve aesthetics, reduce risk of acidification and reduce risk of oxidation.  Godfrey’s 2002 article showed that EDTA or diammonium citrate on bone or ivory strips the calcium and demineralizes the substrate.  If you stir in calcium hydroxide to a 1.1molar strength, you can do a treatment for up to 40 days that works better.  The problem was that good iron removing chelating agents pulled out Ca because the calcium complex is less stable than the iron complex.  Adding in calcium helps. 

The Use of an Electric Field for the Removal of Alum from Treated Wooden Objects

Iben V. Christensen, Lisbeth M. Ottosen, Poul Jensen, Inger Bojesen-Koefoed, Hartmut Kutzke, Mikkel Christensen, and Tom Sandstrom

Alum was used extensively in the Scandanavian countries for waterlogged wood until 1960’s.  Examples: Hjortspring, Oseberg, and Arby.  Alum did not penetrate very deeply, so inner part of the object often left unimpregnated.  Internal cracking happens.  Alum makes wood heavy and brittle, but not stronger.  This experiment put kaolin clay poultices on both ends of the wood with electrodes in the clay so you would not have to put screws in the wood.  Trying to make the potassium and aluminum go to the cathode (has citric acid there) and the sulfate to go to the anode (has CaCO3 there.)  Have to soak it in water so that the ions can migrate? No, but RH needs to be around 90%.  Took 3-4 days, at 4V and 3-5mA current.  There was no significant removal of aluminum, but there was good removal of the sulfate and the potassium.  Problems: possible electrode reactions, humidity needed,  risk of unexpected migration of ions, and that the removal was incomplete, maybe 70-80%.  If I understand correctly, the typical method for retreating objects treated with alum is prolonged soaking in water, and maybe this is hard on the delicate degraded objects, so coming up with a method like this where you didn’t have to submerge the artifact would be an improvement?

Past Conservation Treatments and their Consequences: the Oseberg Find as a Case Study (peer reviewed)

Susan Braovac and Hartmut Kutzke

The Oseberg sleds date from 834AD and were excavated in 1904, treated with alum sometime before 1914, and are unstable now…weak and very acidic (pH of 1) with pieces starting to fall off.   The treatment involves alum (aluminum potassium sulfate) dissolved in 90C water, a coating of linseed oil and a final lacquer.  Alum did not fully penetrate, only going in 5mm across the grain.  Cracks and voids inside the wood not easily seen.  Aluminum makes lignin complexes?  Is sulfuric acid being produced inside the wood?  Question is, now does the alum need to be removed, or is there a material that could be added to stabilize things?

Reconservation of Wood Treated with Alum in the 1920’s – Challenges and Strategies.

Inger Bojesen-Koefoed

We must be respectful of past efforts.  Otherwise, many of these objects would not be here at all.  Some kinds of objects look very different on exhibition as a result of their treatments and it is difficult for the public to interpret what that means.  Conservation history is another dimension of an object’s history.  Alum was invented as a treatment in 1859 and was popular for about 100 years.  It was the first method used to preserve archaeological wood.  There was shrinkage and collapse, often, and the wood looked dry after treatment.  Glycerol was added in 1900 as a possibility, but that went badly.  By the 1960’s PEG began to be used.  There was an attitude in the 1970’s and 80’s that all the alum treated wood needed to be re-treated with PEG.  There is a certain fashion aspect of conservation in terms of what an object ought to look like.  There is also the joy of learning a new method that makes these aesthetic sensibilities change, too.  Conservation treatments and the way archaeology was documented in past eras is really interesting and should be part of what we try to preserve.  If an artifact is stable, resist the urge to re-treat it in the latest fashion.  Consider leaving those old fills and old mountmaking styles in place as its own documentation.   

Accelerated Aging of Recent Oak, Impact from Iron Ions and Oxygen on Mechanical Properties in the Longitudinal Direction (poster)

Gunnar Almkvist, Charles Johansson, Ingela Bjurhager

Known that iron2+ in the Vasa is contributing to iron catalyzed processes in the wood (Fenton type reactions?) , they attempted to impregnate fresh oak with iron ions.  They think that the changed wood preoperties from the use of PEG occur in the radial and tangential directions because the PEG reduces the compression strength, but the iron affects the axial tension strength.  They found a 39% decrease in strength.  What about the ability of sulfur and PEG to inhibit degradation from iron? 

Removing Iron Compounds from a Waterlogged Wooden Gun-Carriage Using the Chelating Agent DTPA (poster)

Ebba Phillips and Inger Nystrom Godfrey

Needed to treat an oak gun carriage that was eroded, cracked, and had high levels of iron and sulfur.  Problem with citrate or EDTA is that you cannot put it down the drain.  DTPA (diethylene triamine pentaacetic acid) is a chelating agent that can be poured down the drain.  They used only 1%, which is half of what others have used, in 1000L of water, and removed a kilogram of iron in the first 40 days.  You need to do analysis of how much iron is coming out so you know when to renew your system.

Excavation and Stabilization of a 17th Century Wicker Basket: New Application of a Known Method

Jill Barnard, Liz Goodman, and Nancy Shippen

Nancy Shippen is now at the MAC lab.  In 2006, a 17th century willow basket was found in a controlled excavation and block lifted.  There were 2.5cm concretions inside.  They sprayed it with 20% PEG 200 and then 20% PEG 4000.  It was then vacuum freezer dried.  But how to remove the concretions?  They decided on glass beads of 44 micron diameter that have been used on bone, as the round shape of a glass bead was less likely to become embedded in the basketry.  They used the lowest setting on the machine, a scalpel, bamboo and compressed air.  Found this to be rapid and gentle, and they brush consolidated with 5% Butvar in IMS as they went.  When pieces came off (the willow had some intact bark) they used 2-3% Klucel G.  On the interior, they did leave some crusts in place if they were too tenacious.  Jim Spriggs comments that he’s had some success with vacuum tweezer in these situations, too.  Someone asked if the accretion could have been a clay meant to be there, but it seems the entire matrix was this material, so no, it was not meant to be part of the basket. 

Ship Caulking – the “Leftovers” from the Ship Conservation Projects (poster)

Anette Hjelm Petersen

Caulking between ship planks made of wool soaked in tar is removed during conservation in order to treat the wood as well as get a good look at the tool marks.  But there might be interesting information in that caulking material.  In the period 1015-1450, textile are rare in Danish sites.  When was the caulking material unspun yarn and when was it textile?  Are there differences in the caulking material between warships and merchant ships?  She is exploring these issues.

Rehabilitation and Monitoring of Waterlogged Archaeobotanical Remains from Southwest Florida’s Pineland Complex.

Donna L. Ruhl 

Unfortunately, there was no presenter for this poster.  The abstract involved a site excavated from 1988-1995, dated 50-1710AD.  The archaeobotanical collection including things like seeds and wood is being curated at the Florida Museum with some grant funding from the National Endowment for the Humanities.  Because this was the last day of the conference and I didn’t know there was no presenter, I missed the chance to look at the poster.

Conservation of a Marine Composite (Copper/Textile) from the 19th Century Shipwreck “Patris” in Greece

P. Patsiri, C. Margariti, S. Rapiti

The Patris was a wheel steamship sunk in 1868 in the Aegean sean, with its two halves at different depths.  It was recovered in 2006.  The object being treated was a firehose fitting, where the hose attaches to a hydrant.  Calcareous accretions were removed with 10% formic acid on a local compress, and they also had 1% Hostacor in deionized water.  The fiber ID indicated the hose material was flax or hemp with a little bit of cotton.  There were also wood traces, but not enough to ID.  The hose also suffered from active corrosion as bronze disease and secondary deposition of copper as newly formed cuprite.  Sodium sesquicarbinate was used to treat the copper alloy.

Check out additional posts on the business meeting, specific WOAM personalities, the flavor of WOAM, and Lars Andersen’s advice to me on freeze drying at the AIC’s news blog.


WOAM 2010 in Greenville May 26

June 2, 2010

WOOD CONSERVATION STRATEGIES, METHODS, MATERIAL and CASE STORIES

Bacteria/Fungi: A Growing Concern for Waterlogged Wood

Shanna L. Daniel, James M. Rolston

Queen Anne’s Revenge, Blackbeard’s pirate ship, sank in 1718.  Lab site has EPA and East Carolina University regulations about what biocide can be used.  They have no sewer out there, and it is a protected wetland.  Following Dawson (1987) they wanted a biocide choice that would be effective, resistant, non toxic, and compatible.  Wanted to use Kathon CG (isothiazolin) by Rohm and Haas, but it wasn’t covered by the EPA.  Chose Proxel BD 20 (1,2-benzisothiazolin-2-one) by Arch Chem.  It breaks down in 9 months (or UV exposure) into non  harmful organic compounds that can be washed down the drain.  Did 8 week test.  Some slight change in pH and color of wood, water turns brown when you use it, didn’t think it was harming the wood, seemed to control fungal activity but maybe not all the bacterial activity.  Need to use around 0.2% in reverse osmosis water, and would be good to circulate it.   Discussion involved use of UV, chillers, Jacuzzi filters, and if it is good to circulate the water or not.  Circulating keeps it oxygenated, but can cause more biological growth?  Report of anoxic areas under timbers getting black staining if you don’t circulate the water a bit.  People felt concerned about ozone being too reactive of a chemical.

Strategy for Testing Impregnation Agents for Waterlogged Archaeological Wood—Examination of Azelaic Acid as an Impregnation Agent (peer reviewed)

Nanna Bjerregaard Pedersen, Poul Jensen, Knud Botfeldt

Gilles Chaumat suggested at last WOAM maybe we should try azelaic aicd.  Soluble at 50-70C but solid at room temp.  Hope that it would crystallize in the wood and provide support and stabilization.  Looking into this idea was the point of the paper, but the more useful product of the paper was actually an new methodology to test new impregnants:

  1. Compile physical and chemical properties through literature search/ experiment
  2. Swelling/sorption capacity (easier to test on sound wood)
  3. Experiment on test and archaeological samples
  4. Potential degradation
  5. Long term stability

Last two steps take more effort, can abandon the candidate if earlier steps do not go well.

Azelaic acid is less hygroscopic than PEG, has other advantages, but it damaged test samples of beech veneer.  Microbial degradation reported in literature search.  Solution is hot and acidic.  Damages well preserved wood.  Cannot be recommended.

Study of the Azelaic and Palmitic Acids Association to Treat Waterlogged Archaeological Wood

Gilles Chaumat, Lionel Blanc, Christophe Albino

High consolidation power, H bonding stronger than PEG.  What about palmitic acid?  Cheap, ecological, non toxic, no acidification, MP close to PEG 4000, other advantages.    NOT water soluble, so how to get it into waterlogged wood?  Tried to dissolve it into azelaic acid, didn’t go well.  What about neutralizing the azelaic acid with KOH?  Also, its conductivity could be a marker for presence in the wood, nice way to monitor where it is going.  KOH could make a lower temperature possible for treatment as well.  Like PEG, you have to use more if you are going to freeze dry.  15% azelaic acid with 84% water and 1% KOH and then freeze dry was OK for very degraded wood, better if you then applied 100% molten palmitic acid at 70C.  Not fully satisfactory.  On a side experiment, there was some passivation of iron by palmitic acid in water.  Azelaic acid doesn’t do it.  Some promise there?

Dimensional Stability and Ultrastructural Features of Waterlogged Wood Reinforced by Pure Feather Keratin (peer reviewed)

Rie Endo, Junji Sugiyama

I was delighted to hear this talk, and I see this kind of paper as indicative of the welcoming, curious, and professionally polite attitude cultivated at the WOAM conference.  The feather keratin treatment is not “shovel ready” as they say, since there are parts of the treatment that don’t go as well as desired.  But the fact that people present papers like this at WOAM and they can be discussed is a beautiful thing.  Waterlogged organics are so very challenging, there would be no hope of making good progress together if this group were not so accepting.  Keratin is not a single material, but a complex of sulfur containing proteins stabilized by disulfide linkages.  To get the keratin, they use duck feathers and laboriously wash, mill, weigh, treat with sodium hydroxide, neutralize, concentrate, and then impregnate wood with up to 40% of this keratin material (molecular mass 1200-1700.)  the material is called “duck feather hydrolysate”.  Seems to have a lot more moisture content than the PEG treatments, and more swelling, unfortunately.  Maybe because the agent contains a lot of salts?  Her samples included Chinese Soapberry and Oriental Elm.  Seems like the keratin penetrates the middle lamella and reinforces it, forming an amorphous structure in the wood cell walls.  Because of where it goes in the wood, it seems like removing it again would be difficult.

Keratin as a Bulking and Stabilization Agent for Collapsible Waterlogged Archaeological Wood (peer reviewed)

Poul Jensen and Kristiane Straetkvern

R. Endo initially presented the feather keratin treatment idea at the Copenhagen WOAM meeting in 2004.  To look into it, the Danes were following the testing strategy proposed by Nanna Bjerregaard Petersen et al in their paper on azelaic acid.  The Danes seem to like this protocol and plan to keep using it.  Maybe the rest of us should follow suit?  Someone asked why we don’t cut to the chase and just test the material in mock-ups, but indeed some of this important work happens because of the needs of student projects, so that is partly why the first few steps are done this way.  They found that the keratin was water soluble up to about 50% at room temp and had a molecular mass around 1500-200.  They saw 2.6% weight loss in drying and decomposition at 160C.  pH 6-7 in aqueous solutions depending on concentration and they can’t seem to find a solid phase…it has no freezing plateau, suggesting a eutectic?  Not good for freeze drying?  In testing, they were getting a lot of shrinkage and even up to 40% could not prevent collapse in deteriorated samples.  However, there seems to be good penetration for fresh wood?  Maybe it might be OK as a surface stabilizer, but it is not recommended for degraded wood.  There was discussion about feather keratin afterwards, including speculation it might be better for treating proteinaceous materials instead of cellulosic materials.  Horn in the UK, for example, turns up very degraded in the rare situations when it appears.  However, delegates who work with proteins a lot thought this was a dangerous idea, in part because important analysis by sulfur isotopes would be ruined.  How could you distinguish from the original sulfur?

Preliminary Assessment of a New PEG

Clifford Cook, Jessica LaFrance, and Carmen Li

They were testing PEG POSS, PG1190 and PG1191, a product much like PEG 3350 except its chemical structure has a cage-like shape at the central core and it is liquid at room temperature instead of a solid like PEG 3350.  From the discussions at the conference, having PEG be liquid at room temperature, like PEG 400, is a little bit of a problem because you always get the movement of the liquid inside your wood, the system continues to be doing things (who knows what?) and of course the oozing out and high RH issues of the low molecular weight PEGs.  PEG POSS seems to be even more corrosive to metals than the PEG we use now.  He was testing the new product against other common treatments, and using waterlogged samples they’ve had in the CCI lab for many years.  Tidbit that those sample are actually more degraded now than they were years ago.  This reflects what we have suspected about storing waterlogged wood in our labs: it is getting more deteriorated as we store it.  Sidenote from me: archaeologist Kitty Bernick told me she thought baskets that were treated right away seemed to fare better than ones where treatment had been delayed.  Sharp cookie, that Kitty.  I’m including some notes on how he did the common treatments, because people might be looking on the web to see how CCI is doing it these days and the older literature isn’t always the same as today’s methods (case in point: the C.Wayne Smith published text on the silicone oil treatment being outdated from the way his lab does it today.)  In a perfect world, people about to do the treatment would call or email those with the latest methods.  But people don’t often do that, do they??  So, it took two weeks to impregnate the samples of PEG POSS, measuring their uptake and stopping when they stopped gaining weight.  At both 20% and 30% the samples started getting darker.  Also, in testing with metals PEG POSS is more corrosive than traditional PEG.  And much more expensive.  For traditional PEG, he increased concentration in 10% intervals every 3 weeks until he had 40% v/v PEG 400 and 50% v/v PEG 3350.  He also heated at a hotplate on lowest setting of 48C and said something like” of course we would never heat PEG today…”  I’m very intrigued by that and asked around quite a bit at the conference…heating PEG is known to break it down, and most folks think that means that bits break off the ends of long chains, not that long chains get broken into much smaller bits by breaking nearer the middle.  And certainly formic acid is one of the things that is formed, as illustrated by Mortensen et al’s paper where they are trying to use formic acid as a marker.  But I cannot seem to find out how bad this breakdown is for preservation of the wood itself…you do get some benefit from heating in terms of penetration…is that worth it?  Another tidbit, rinse off your sample in water well before drying…the excess PEG that leaves white crusts can be removed later too, but it’s much easier to do it in this step here.  Back to the common methods, the CCI gang was also testing sucrose with 1% Kalpon CG biocide by increasing concentrations by 5% till they got up to 40% and then the increase happened at 10% intervals every few weeks.  Some folks see benefits in sucrose treatments, but I am still skeptical because they are more hygroscopic than PEG from what I understand, and also because of the IPM issue.  They got very poor results with both silicone oil and with acetone/rosin.  There was lively discussion about why the silicone oil treatment went poorly, and possibly it wasn’t executed properly.  But this leads me to think, if CCI (with its tremendous reputationand experience!!)  has trouble executing a silicone oil treatment, and the consequences of failure with silicone treatment are so final, then isn’t that an indicator that it is a risky treatment?

Conserving Waterlogged Archaeological Corks Using Supercritical CO2 and Monitoring Their Shrinkage Using Structured-Light 3D Scanning

Stephanie A Crette, Nestor G Gonzales, Benjamin Rennison, Michael Scafuri, Paul Mardikian, Michael Drews, and Marthe Carrier

Okay, so for some reason I don’t fully understand (but lots of people say it) cork does not respond well to PEG.  Maybe because of hydrophobic suberin in the cork plant cell walls?  And it comes up archeologically more often that I realized…bottle corks, cannon bungs and the like.  So supercritical drying has been a method to look into that.  Remember that pesky water issue in wet stuff, which in a simplified form for us treatment-based grunts at the bench seems to be 1) get the water out without the high surface tension of the water causing the violent stresses of capillary action and 2) provide some sort of support to replace the support the water gave.  OK, that’s crude but in in-a-nutshell.  Solving problem #1 often involves freeze drying, since you jump right from solid to gas and don’t HAVE the liquid to do the capillary thing.  But supercritical drying solves that issue too by using CO2 which acts like a liquid and a gas (that’s the supercritical part I think.)  Water is not soluble in CO2 because its surface tension is too high, so you have to exchange the water in the corks with something else, like methanol, that works well with the CO2.  This takes maybe 20-45 days.  Shrinkage is in the 2-4% range.  This treatment has been done before on cork, but the new thing with this paper seems to be the examination with a Breuckmann Opto Top-HE Structured Light Scanner, using the Geomagic Studio V8 software (but apparently PolyWorks V.11 is more current.)  Seems like this gives good results, but I don’t know if the cork is robust enough…there’s nothing in there to support the structure, right?  EUREKA MOMENT for me: isn’t cork a bark?  Like our cedar bark on the Northwest Coast?  And isn’t it having the same trouble with PEG treatment?  Ergo, I need to pay attention to the cork literature, because I wasn’t before.  And seriously, if we can nail down protocols for spruce root and cedar bark, there will be thousands of baskets we can maybe treat better in the future.  And also my whole obsession this week with thinking about baskets on the NWC as being kind of like ancient Greek pottery: the ubiquitous vessel in the culture which in some cases was elaborately decorated with designs that held meaning we really want to know about.  Who was the Tlingit Euphronios??  I never thought about things like that before.  And tell me a Chilkat robe is not technologically as amazing as a Greek vase.  God, I get so excited about this stuff!!!

Evaluating Treatments for Waterlogged Lignum Vitae Objects from the USS Monitor (peer reviewed)

Elsa Sangouard, Susanne Grieve

The Monitor: a civil war ironclad sunk in 1862 off the coast of North Carolina.  Lignum vitae, a ridiculously hard, dense wood from a tropical evergreen tree with a high resistance to decay and a resinous quality that made it good in friction situations such as those in pulleys, block sheaves, deadeyes, and the like.  They tried controlled air drying (best results, 14% weight, looked nice), PEG 400 (didn’t get proper freeze drying? Got cracks), sucrose (10% weight loss, no cracks, discolored and there’s the problem of sensitivity to high humidity and pests), acetone rosin (17% weight loss, unsuitable), lactitol trehalose (cracks and too harsh, but 5% weight loss.)   Seems like controlled air drying works, so why not do that and avoid putting stuff in the wood if you don’t have to??

Conservation of the Newport Ship: the Challenges of Scale.

Sophie Adamson

A 15th century trading vessel found in South Wales in 2002.  Some 1700 timbers excavated in two phases, stored in 16 freshwater holding tanks and recorded with laser scanning technique.  Condition survey in 2007, and then all timbers cleaned in 2009.  Timbers in pretty good condition, there seems to have been tar on it?  Lots of wet textiles and organics still await analysis.  Finding a French silver coin with the date 1446 was quite nice.  Did have some problems with sulphur and anoxia, people felt ill while cleaning the tanks.  Challenging to get the iron out…were trying to use 2% ammonium citrate, didn’t get out all the iron but needed to move forward.  Undergoing two-step PEG treatment (I think the wood was beech?) and expecting it might take two years, looking towards reconstruction in the next 4 years?

The Yenikapi Shipwrecks: Dismantling Methods and First Step to Conservation

Ufuk Kocabas and Isil Ozsait Kocabas

Our jaws dropped.  What a presentation!  The excavation going on there is happening on such a huge huge scale.  Imagine an ancient 11th century Byzantine harbor in one of the most intense heritage areas in Istanbul.  Now subtract the ocean and just leave all that waterlogged stuff under the sediment.  A 58,000 square meter excavation.  And then get a huge amount of money to put in the world’s largest underwater tunnel and put those elements all together.  Bam!  100 specialists.  600 workers.  34 shipwrecks exposed since 2005 (22 lifted so far.)  10 wooden piers, lots of horses, 25,000 artifacts (many of them organic).  Things like a ship with a cargo of amphora, 5 warships, another ship with the personal belongings of the captain intact, a boat with olive pits, cherry stones and a reed basket (cherry pits seasonal for May and June!) Then he shows us these amazing photo mosaic studies…over 200,000 digital pictures have been taken and some of them are knitted together in photoshop to make images of each excavation phase and even print them out 1:1 for exhibition.  The wood of the ships is very deteriorated and they’ve got some elaborate techniques for lifting the planks (negative mould method, L-shaped carriers, epoxy support, and “hamburger method”).  Two labs at Istanbul University are treating the timbers, using 10% PEG 2000.  Is it any wonder the group is leaning heavily towards WOAM 2013 in Istanbul?  I can already taste the raki!!

Conservation of a Waterlogged Mayan Paddle

Wayne Smith, Helen DeWolf, and Heather McKillop

The paddle from Belize was made of Manilkara sapote, a wood in the family Sapotaceae.  The wood contains high amounts of gummy latex “chicle” (15% rubber and 38% resin).  The client wanted it done in silicone oil as a “sure thing” because it was going to return to less than ideal curation conditions.  The prep phase took 60 weeks, if I understood right, to replace the water, first by exchanging with ethanol and then acetone.  He starts with the bulking polymer, which comes in several viscosities, and the art of choosing which one is important.  Then a crosslinker, MTMS (methyltrimethyloxysilane)  is added 20% by volume of the bulking agent and mixed thoroughly.  Percentages are chosen between 3% and 70%.  You can use MTMS alone to form a resin in the wood, but it is brittle and has no bulking ability.   Key thing with silicone oils is that they must have a hydroxyl functional group or they are just oils like the armor-all at the hardware store and will not work.  Immerse the object in the polymer solution for 6 weeks at ambient temperature and pressure.  A big vat can be mixed up to do hundreds of artifacts…it can last 5-6 years.  So this polymer solution naturally bonds to the remaining structure in a thin overall layer everywhere, but it won’t stay, and it won’t fill voids.  No panic to hurry at this stage, you’ve got a few weeks with these things out in the open air to adjust the surface how you like it.  They finalize the treatment with a tin based catalyst, dibutyl tin diacetate (DBTDA) which makes an acetic acid by-product, but that’s gone up the fume hood in a few days.  Catalyst is applied by vapor deposition in a polyvinyl bag.  The polymer is most heavily accumulated in the compound middle lamella and the primary cell wall.

I learned a TON about silicone oil treatments at this conference.  And it was hugely valuable to have three people at the conference from the lab at Texas A&M University where the treatment is done extensively: C.Wayne Smith, Catherine Sincich, and Carlos Cebrera Tejedor.   Conservators outside that lab have really held silicone oil at arms length.  (And perhaps wished their arms were even longer.) Here is a massive oversimplification, but in trying to understand why this is so, in a nutshell C. Wayne Smith seems satisfied that the important questions about silicone oil have already been answered, but other people still have questions.  I think Catherine and Carlos still have questions.  And I think those questions fit into the larger holistic issue of conservation standards and ethics as represented perhaps by the AIC philosophy, which has many points of divergence from the philosophy of many in the world of maritime archaeology.  I think that is at the heart of the controversy about silicone oil.

Twenty-Five Years Later: The Treatment and Display of a group of XVIIth Century Boats.

Andre Bergeron and France Remillard

The work on this was done from 1984-1988, and typical of that time, there was little money, little expertise, some PEG available, and lots of determination.  Boats found at the entry to the St Lawrence River, and there was not a lot of time to take them out.  They used PEG 400 and did some reshaping, tried to freeze dry them outdoors in a shelter and noted that the weight loss related very closely to the amount of sunshine, but also to the wind (with a slight lag.)  It has been reconstructed and on display a few times, at least 10 million people have seen it.  The project is an example of how the conservator can be the last line of defense to save an artifact.

PEG discussion: oh my this was interesting…the Danish National Museum has been skipping using the low molecular weight PEG now in pre treatment for freeze drying because it doesn’t solidify.  It acts like a cryoprotector, but so does the high molecular weight PEG.  With the liquidness of the PEG 400 in the structure, there is concern for it being hygroscopic and the salts moving around and being active.  And of course PEG 400 is still a liquid after treatment, it doesn’t magically become a solid.  Denmark was treating highly degraded objects with 25% PEG 2000 and 5% PEG 200 and it looked OK but was very vulnerable to high humidity.  So they dropped the PEG 200 and just use PEG 2000 now with better results.  They report a little bit of cracking on timbers, but find that acceptable.  CCI still likes a two-step method with low molecular weight being used to counteract cell shrinkage and high molecular weight to counteract cell wall collapse.  Cliff Cook gave a great two-minute synopsis of the history of low molecular weight PEG: Stamm started using it in the late 1950’s to help the cell wall of green wood during oven drying.  Ambrose came up with the idea of freeze drying with it.  Dave Grattan and Cliff Cook recognized PEG 400 was good for reducing the shrinkage of the cell wall (as opposed to cellular collapse, which is counteracted much better by high molecular weight PEG) and they came up with the PEG CON computer program to determine how much PEG 400 you need based on the deterioration and species of wood.  If done right and the PEG 400 replaces bound water in the cell wall, it is not sloshing around inside the wood.  Others in the room seem to think now that PEG 400 is not compatible with freeze drying.  However, Susanne Grieve reports that she has visually examined hundreds of artifacts that did well with a treatment of PEG 400 followed by freeze drying.  People discuss if we are maybe getting micro ice crystals and damage, and if water is evaporating instead of sublimating in the freezer.  Some folks report that if you aren’t getting the low molecular weight to freeze, then you aren’t getting freeze crying and the vacuum would make things worse and force evaporation from the capillaries even faster.  The ArcNucleart lab in Grenoble is not using low molecular weight PEG anymore either because they had some problems with freeze drying.  They think penetration is not an issue, and that they are getting good penetration into cell walls with PEG 4000.  Here’s an interesting tidbit: water and PEG have good affinity, and so do water and wood, but the PEG and wood have less affinity for each other than those other two combinations.  Wow, just when you think the field has made up its mind about PEG, we see there isn’t a single answer, even now after using it for so many years.

From Excavation to Preservation: 17 Years Work on a Roman Barge from Xanten-Wardt

Axel Peiss

Found in 1991 in a gravel pit in a location where the Rhine River used to go.  2/3 of ship present, wood very decomposed, made of 8cm wide planks and the needle would go all the way through when pin tested.  7m long, from around 100AD.  Needed to be salvaged quickly, so the block lifted THE WHOLE THING.  8 x 3 meter block, weighed 40 tons.    Conserved with PEG 200 in 1993-93 and then PEG 4000 in 1996-97.  But the construction of a new Roman Museum in Xanten indicated where this project got interesting.  The architects and designers wanted to suspend this thing from the ceiling!  Well, as you can imagine, talk of the “Flying Boat” was working its way into chatter and banter the whole rest of the conference.  If they had known of this plan to hang it up, a freeze drying treatment might have saved them 500kg.  Elaborate steel strip mountmaking was undertaken, as well as gap filling and some new wood additions.  New carriage bolts were used to hold things together and the heads were reworked to make them look old.  The 3 ton object was hung 10m high (ceiling in the hall is 16 meters) with a 1:10 model of the ship nearby.  The ship project cost at least $680,000 euros, took about 2,500 hours of work.  More than 700,000 people visited the museum last year.  Axel’s museum was one of proposed sites for WOAM 2013, but it seems to be lagging behind Istanbul a bit in crowd popularity.  Some folks were saying, Istanbul 2013 and Xanten in 2016??

Quo Vadis—Do We Need Swimming Pool Stadiums for Waterlogged Wood Conservation? (poster)

Nicole Ebinger-Rist and Ingrid Wiesner

In Germany they are facing a very challenging situation of gas lines being constructed over hundreds of kilometers, lowering of ground water tables from agriculture and more shoreline impacts from harbor construction.  With all the waterlogged wood they are turning up, they are really hoping for better options for the volume of stuff that’s turning up, like maybe re-burial?  Nicole was saying that the big timbers treated with PEG 3350 get very dark and very heavy, and the wood tends to lose it characteristics.  I wonder, why does it get dark?  The tests I did on the spruce root did not get dark until it reached 75%, and then only with the unheated samples.  Is it a matter of penetration??

For those of you like me, who had to look up the phrase “Quo Vadis” it means “where are you going?”  According to Wikipedia, however, it also suggests a Biblical association with the phrase in the context of Jesus going to get crucified.  Hopefully, the situation is not quite that dire in Baden-Wurttemberg??  And yet another tangent, on this very day I read a New York Times article about how great the traditional pretzels are in that very area of the world!  Strange how those kinds of coincidences pop up.

Controlled Drying of Saxon Bridge Timbers from Sucrose Pre-Treatment (poster)

Grace Deeks and Jim Spriggs

We all hear these cases: a project desperately needs to treat an artifact, but has no conservator and cannot afford one.  Can’t we just design a treatment and let the folks there run with it?  Get advice on options, choose the cheapest one, and do the work in-house.  Sometimes yes, but when it goes wrong it can be a real mess without a conservator there with the expertise and resources to troubleshoot.  Common mistakes of in-house treatment seem to be that the undermining chemical principles are not fully understood, so it is hard to recognize when things are going wrong early enough in the process to correct it.  Staff turnover and lack of familiarity in proper conservation documentation means loss of even the simplified understanding of the treatment, and loss of key information that could potentially have reverse poor results (or even learn as much as we could from them so as not to repeat them.)  Maybe it is my imagination, but sucrose treatments seem to be enjoying a bit of a renaissance lately.  Is this because they are relatively inexpensive?  Is it because archaeologists feel more comfortable doing them?  I’m not sure.  But sucrose has some drawbacks…in this case study, the artifact ended up with mostly fructose and glucose, not sucrose, after treatment.  It was grossly infested with wasps over many years, creating a stinking mess.  Fructose is hydrophilic and expands 22% of its weight at 60%RH.  It also deliquesces and you get a wet surface.  Sucrose treatment falls into this category where people like it because they can afford it, but they cannot afford the controlled environment needed to store it.  Without the ability to control RH and insects, this is a lousy treatment option.  And if you do have the resources to control RH and insects, don’t you also have the option to use PEG??  Note: the use of a 40 foot insulated freezer container truck converted to an insulated enclosure for controlled drying seems to be going in a good direction for the current project.

Analysis of Sugars Used for Conservation of pre-Columbian Dugout Canoes Recovered from Lake Phelps, North Carolina (poster)

Fletcher O’Cain, Sarah Watkins-Kenney, John Kenney

“What is this stuff?”  Isn’t that one of the most fundamental question in all of science?  Looking at the Lake Phelps canoes treated with sucrose (Four of the 25 canoes were excavated and treated, they were made of bald cypress.)  20 years after treatment, the canoes have damp, sticky, white-brown surface deposits.  Shouldn’t we have sugar in there because the object was treated with sugar?  Well, no.  Chemical assays with Benedict’s reagent and 3,5-dinitrosalicylic show that hydrolysis is going on and the sugar is breaking down into glucose and fructose.  Confirmed by spectroscopy.  See the Deeks and Spriggs cautionary tale on sucrose also.

The Ability of Waterlogged Woods to Resist Freezing (poster, peer reviewed?)

Hanne Billeschou Juhl, Knud Botfeldt, and Lars Brock Andersen

What about freezing unimpregnated wood  for storage?  Some variables: You can either freeze the wood damp, or you can freeze it submerged in water.  There is deteriorated wood versus fairly sound wood.  There is temperature.  And there are the freeze/thaw cycles of a typical chest freezer.  Seems like if I understood correctly, you can generally get away without microscopic damage if you freeze the wood underwater at not-too-cold temps and avoid freeze/thaw cycles.  But it works better for less deteriorated wood.  Degraded wood expands more, but then it appears to return to near normal size after thawing?  They tested at -10C and -40C.  Water expansion of 9% when it crystallizes to ice is not as important as mechanisms like hydraulic pressure, microscopic lens growth, and dyhydration of the structure.  So then we need to look at pore size distribution, freezing temp, air content in the wood and how many freeze-thaw cycles happen.

Check out additional posts on the business meeting, specific WOAM personalities, the flavor of WOAM, and Lars Andersen’s advice to me on freeze drying at the AIC’s news blog.


WOAM 2010 in Greenville May 25

June 2, 2010

IN SITU PRESERVATION AND REBURIALS

Deepwater Preservation and Management of Arcaheological Sites, Presentation of the DePMAS Project

Elizabeth E. Peacock, Fredrik Skoglund, and Jorgen Fastner

Deepwater distinguished from shallow by whether or not it can be accessed by divers.  Energy exploration is driving the need to consider how to protect these sites.  The area to protect now extends out 12 nautical miles from the coasts of Norway.  Estimated 17% of Norwegian ships from the 19th century were lost in open waters.  Wrecks also play an important role in fish spawning.  Challenges include wave energy, high salinity, steep drop-offs and the teredo worm.  I liked the discussion of “agents of preservation” in addition to the usual “agents of deterioration.”  The project has a 32 year timeframe and is trying to develop guidelines and protocols for cultural heritage management authorities regarding these sites.  Focus includes site formation processes, deterioration mechanisms, develop practices for mapping sites, and in situ preservation protocols.  Related project is RAAR (Reburial and Analysis of Archaeological Remains) which focuses on shallow ocean protocols.  Both have info on how to make and retrieve samples (metal, silicates, wood, bone, organics).  DePMAS is developing methods of monitoring using two sites on the Norway coast and deposited materials with a polymeric site protection mat.

 

WreckProtect – A Eurpoean Project to Protect Wooden Historical Shipwrecks Against Attack by Shipworm in the Baltic Sea.

David Gregory and Charlotte Bjordal

Estimated 100,000 wrecks in the Baltic, maybe 6,000 are known to be of historic and archaeological importance.  Low salinity of the Baltic has seemingly kept shipworm from being a big issue so far.  There are 65 known species of shipworm (teredo) but it is Teredo navalis that they are worried is spreading into the Baltic.  The larvae have about two weeks to find a wooden host, and are a bivalve mollusk similar to a blue mussel but are long and wormlike with a tiny shell on their butt (if I got that right.)  Theoretically, they are spreading into the Baltic for a few reasons: maybe the water is cleaner now, poorer quality wood in harbors may be easier to attack, it may be coming in as an invasive species, or it may be related to environmental change (especially change in salinity.)  There is a phenomenon called the North Atlantic oscillation that maybe causes periods of higher salinity, and there is some data to suggest outbreaks of shipworm may happen 2-3 years after??  The WreckProtect team is made up of marine archaeologists, GIS modeling experts, wood scientists, marine biologists, conservators, and a geochemist.  They are gathering data about the spread of the shipworm and environmental changes, with the project extending from May 2009-April 2011.  Some techniques to stop shipworm in the past have included pitch, tar, creosote, nails, and copper chromium arsenate (not banned yet but might be soon).  Today, geotextiles and plastics are sometimes used to try to cut off oxygen to the worms.  Debris netting (kind of like plastic seaweed) is used to encourage sediment transport as another way to exclude oxygen.  http://www.wreckprotect.eu

Monitoring In Situ Preservation of Shipwrecks

Michel Vorenhout and Wouter Waldhus

Fungal attack tends to happen fast with oxygen, while bacterial attack thrive in absence of oxygen (although their destruction of the wood is slower.)  Looking at shipwrecks buried in the ground in the Netherlands and how the deeper parts of the wrecks have better preserved wood, and being below groundwater seems to be a factor in better preservation.  In 1940-1960, new land was recovered (polders) that had previously been below sea level, so examining wrecks in that area is fruitful.  Development in the area means the groundwater will get lower.  Looked at two kinds of sites: flat coverage and a more interventive raised covereage of a hill that incorporated plastic in the burial to help catch rainwater and keep the water level up.  Both seemed to create anoxic environments, but the latter took longer to recover if it was disturbed, such as for examination.  They will be monitoring 6 more wrecks over the next 2 ½ years.  I had a chance to chat with Michel over beers later in the conference, and he was a wealth of knowledge about the machinations of academia and science and how those worlds work globally.  Not like he has more of this kind of insight than other scientists, but he was able to explain it to me in terms that I could understand and it was really fascinating.

Reburial and Analyses of Archaeological Remains – The RAAR Project Phase II

Inger Nystrom Godfrey, T. Bergstrand, C. Bohm,  E. Christensson, D. Gregory, E.E. Peacock, V. Richards, and I. MacLeod.

Artifacts were reburied in the late 1990’s, plus sample materials in order to evaluate reburial as a preservation method.  Hoping to learn about effects of the reburial environment as well as link environmental parameters with degradation.  A collaboration of various institutions is looking at six areas: environmental monitoring, metals, ceramics/glass, wood, non-wood organics, and packing and labeling materials.  They are looking at a metals reburial trench, an organics reburial trench, and one that is undisturbed.  The project is meant to last 50 years.  In sediment cores, they were looking at porosity, particle size, iron, and organic content.  In studying pore water, they looked at oxygen, sulphate, sulphide, CO2, redox potential, and pH.  They had a reburial of organics in 2002 and metals in 2003, but didn’t have the funding they needed to follow up in 2008 and 2009 as much as they wanted.  They did find that on metals, corrosion decreased with the depth of burial, but still occurred to an unacceptable level.  All metals, esp. ferrous need burial deeper than 65cm.  Reburial is a tool, but not a way to dump unwanted collections.  The article in the proceedings will perhaps describe more fully which materials fared well and which did not, and I’m hesitant to go into that much here for fear of oversimplifying the results and doing a disservice.  There are some worthwhile findings, and I look forward to reading more about interpretation, since I think the researchers have mixed feelings about it.  There are packing and labeling materials that did well, however, including HDPE crates, ziplock bags, pencil, permanent marker, and DYMO on PVC.  Polyethylene net, polyester, DYMO on steel, ballpoint pens and archival pens did not fare so well.  In Sweden, a museum would still be responsible for the burial site as a storage location of collections.  Heritage agencies need better accession and deaccession protocols for this kind of material.

DEGRADATION AND STABILITY STUDIES – ANALYTICAL TECHNIQUES

Bone, Antler and Ivory as Environmental Markers in Marine and Lacustrine Environments

Gordon Turner-Walker and Kristina Gau

Organics are so sensitive to change in the burial environment that survival may mean the burial environment has not changed much?  Mineralized vertebrate tissues are really durable, hydroxyapatite is the insoluble inorganic salt responsible for that preservation, and it has a mutually protective relationship with the protein collagen also found in bone.  Calcium carbonate, for example, is 100,000X more soluble.  If the material were not so robust, you’d dissolve yourself!!  Gordon talks about “diagenic trajectories” and has a lot of info about the pattern of deterioration seen in bone from different sites.  For example, dry site bone had increased porosity near the edge, but that was not seen on the waterlogged one which had overall cracking and no additional porosity.  It had some “bacterial magnetite biomineralization” which is a precursor apparently to fromboidal pyrite that he sees in a lot of samples from really old bone.  Freshwater bone gets damage from cyanobacteria, but they need sun because they photosynthesize.  In a well drained aerial soil he will see very porous degraded bone with bacterial tunneling, but the surface is intact.  I had a little bit of a hard time following some of this, but in essence you can correlate the histological features with the burial environment.  You might see pyrite framboids inside a tunnel from bacteria, which gives you a sequence clue.  The oldest bone he examined was up to 700,000 years old.  He said a lot of this was already published, but all of it is new to me so I cannot tell you what is new to the WOAM folks.  Gordon Turner-Walker teaches in Taiwan, and from what I could tell from the conference, this is really a “bone guy” who seems to have a lot of interest and expertise in archaeological bone.

Studying and Manipulating Bacterial Wood Decay – Results of Laboratory Experiments

Jana Gelbrich, E.I. Kretschmar, Norbert Lamersdorf, Holger Militz.

In order to study bacterial decay it would be helpful to isolate the bacteria, which has been difficult to do in the past.  In this study, a microcosm was developed using live waterlogged sediments as well as some infected wood in a closed system with certain variables: air, air plus oxygen, nitrogen (anoxic) or air plus circulation.   Sound pine wood in the sediment kept in the dark at 20C for up to 13 months.  Circulated treatment had the most decay.  The current ways of classifying the deterioration are not precise enough to use here?  In another microcosm test, small glass jars were used with air inflow and different sediments: pure, nutrition poor, and added nutrients (nitrate or ammonium, phosphate or sulphate).  Increased nutrients in the sediment correlated to less wood deterioration.  Later on in the Q&A, I asked if this was an avenue for preservation storage reburial: add nutrients to the sediment to keep the bacteria from eating the wood.  Generally, it was thought that might be dangerous, polluting, and cause an explosion in the bacteria population.  I still can’t help but wonder if it would work in short-term reburial with a way to remove the “food source” and the bacteria with it, then replace that bacteria-chow station, kind of like a cockroach hotel.

Environmental Scanning Electron Microscopy (ESEM): An Effective Analytical Tool for Comparing Reagents Used in the Conservation of Waterlogged Wood

Catherine Sincich

ESEM has the big advantage that you can put wet sample in the chamber.  Sputter coating is optional.  You also don’t need high pressure.  Can put just part of the object on the stage and let the rest hang down inside the chamber.  She was using it to determine when impregnation was done, in order to make treatments more efficient.  Also mentioned other research that indicated the silicone oil made a nice coating on some wood structures (like around the openings of resin canals) that could not be seen easily with the ESEM, and that the CT scan is useful for determining degree of penetration of silicone oil.

Evaluating Long Term Wood Stability of Waterlogged Archaeological Wooden Objects Through Determination of Moisture Sorption Isotherms and Conductivity in Conserved Objects and Impregnation Agents. (peer reviewed)

Poul Jensen, Anne Christine Helms, and Mikkel Christensen

This talk was over my head.  Here are some tidbits I think I got: Alum treatment stable to a very high RH unless you also use glycerol with it.  Big difference in moisture content between mannitol and sorbitol?  With PEG treatment, there seems to be a big drastic jump in conductivity at a specific point, over 50%, sometimes in the 70% or 80% range.  Happens at lower RH for the mixed molecular weights?  There is some key point here about ions moving around and the system not being totally stabilized even when we thought the RH was OK.  This seems to be because the conservation materials we put into the wood (specifically PEG 200-600, glycerol, and sorbitol) increases the conductivity, even at RH below 50%.  If I understand right, if ions are free to move around inside your objects, there is increased risk of chemical actions going on in there, maybe some that you don’t want?  This talk seems to provide more ammunition in the argument against using low molecular weight PEG in our artifacts if we can avoid it…

Formic  Acid as a Marker Molecule for Polyethylene Glycol Degradation in Conserved Archaeological Wood – A Radiocarbon Study (peer reviewed)

Martin Nordvig Mortensen, Helge Egsgaard, Soren Hvilsted, Jens Glastrup

“I’m going to explain some experiments today that didn’t work out as I planned.”  What conference have you ever been to that you could get up in front a crowd and say that??  Well, maybe the Western Association for Art Conservation, but it is a rare and beautiful thing to put yourself out there in front of your colleagues like that and do so in safety.  The premise here is that when PEG breaks down, one of the products is formic acid, and that C14 dating of that should reveal very old dates since PEG is petrochemical, and formic acid from the wood should be historic in timeframe and could be subtracted out.  Turns out the extraction of the formic acid was frustrating due to the difficulty of avoiding contamination and great efforts were made but the numbers were still a bit strange.  Also seems like formic acid concentrations in conserved archaeological wood is quite low (this is good news for me if I want to heat my PEG treatment?) Turns out, however you interpret the data, it looks like the C14 from the Vasa is at least 88% petrochemical and perhaps totally ancient and therefore all from the PEG, so PEG degradation has definitely taken place.  This method, however, cannot quantify that.

Oxygen Measurements in Conserved Archaeological Wood (peer reviewed)

Henning Matthiesen and Martin Nordvig Mortensen

Looking at oxygen consumption (might give you a decay rate), oxygen concentration inside the wood (might help you determine ways to control the decay process) and oxygen diffusion into wood.  Using optical oxygen measurement based on fluorescence that the oxygen quenches.  Helpful to put the sample into Escal heat sealable oxygen barrier film.  Conserved wood is not anoxic, only waterlogged wood is anoxic.  If you can control the concentration of oxygen inside by diffusion, maybe we could choose to make the wood anoxic.  When flushing with nitrogen, it took more than 200 hours to turn it anoxic. 

 

Waterlogged Wood from the Miocene Forest of Bukkabrany: A Preliminary Investigation of Material Morphology and Chemistry (poster)

M. Petrou, G. McConnachie, and A. Pournou

7 million year old forest, un-mineralized.  Had both fungal and erosion bacteria.  Lumen filling treatment rather than cell wall bulking was recommended.  Intriguingly, there is an image that says, “separation of the compound middle lamellae from the secondary wall.”  Is there still secondary cell wall?  Is it devoid of any carbohydrates for low molecular weight PEG to bond to?  Some data seemed to show abundance of inorganic inclusions.

The Stirling Castle Wood Recording Project (poster)

Angela Karsten and Graeme Earl

Looks into old and new techniques for recording fine surface detail before it is compromised by treatment.  Old methods include photography, drawing, x-rays, and silicone molding casts.  New ways include PTM (polynomial texture mapping) and laser scanning.

 

Measurements of Responses in Archaeological Wood to Ambient Temperature and Relative Humidity – A Case Study – The Oseberg Ship (poster)

Maria Jensen, Paolo Dionisi Vivi (shown here in the trunk of Susanne Grieve’s car), and Susan Braovac

Using a measurement system designed to measure movement in panel panels, the system was applied to an old oak ship that had been treated with linseed oil and creosote and held in place with lots of nails.  Compared to unrestrained fresh and archaeological samples, there was  a lot less movement on the constrained ship.  Are there stresses there that might be harmful to the ship?  The exhibition is in an uncontrolled environment.

Mapping PEG Diffusion into Waterlogged Wood Samples.  A Low Tech vs High Tech Approach (poster)

Jessica Binham, Rohan Patel, Sanjana Vasnani, Sarah Watkins-Kennedy et al

 The abstract was submitted with one set of results in mind, but they were only able to get one data point ten times…press the wood against the high RI crystal to get a nice band in the ATR spectroscopy, but didn’t get a series at different percentages because the sample didn’t have that variability.  Ultimately, they are hoping to figure out a way to determine optimum soaking time for PEG treatments, as the current methods is sample intensive and destructive (gravimetric techniques) and they were hoping infrared spectroscopy could give a better method.

Check out additional posts on the business meeting, specific WOAM personalities, the flavor of WOAM, and Lars Andersen’s advice to me on freeze drying at the AIC’s news blog.