“Blow It Off: Moving Beyond Compressed Air with Carbon Dioxide (CO2) Snow”
L.H. (Hugh) Shockey
One of the great things about coming to AIC is putting a name to a face and somehow I didn’t expect this guy to have a beard and ponytail and look like he could have just been working on his hot rod. When one of his slides identified his initial “L” as standing for Lucian I was tremendously amused, as just last week I watched a movie marathon with the three “Underworld” movies about vampires at war with werewolves, and guess who is the charismatic king of the werewolves? Lucian. OK OK on to meaningful content.
He’s working at the Lunder Center at the Smithsonian’s American Art Museum, and exploring the potential benefits of CO2 snow, which is producing particles on the micrometer scale, not the millimeter size. Kind of like dry ice blasting, but on a much smaller, finer scale. Setting up the equipment is in the $3000 range, and requires at minimum a snow generation nozzle and a source of compressed CO2 gas or liquid. The geometry of the nozzle is pretty specific and requires a specialty vendor. He was referring to a “Venturi” nozzle, but I don’t know what that means. His equipment is more elaborate with more ways to make the delivery more controlled and efficient. How does it work? Primarily, Hugh describes it as a “momentum transfer surface cleaning technique” sort of like billiard balls knocking dirt off the surface. Other forces at work might include secondary effects of liquid CO2 briefly touching the surface, breaking weak van der waals forces, and so-called “freeze fracture” although you’re never getting below the freezing point of water so Hugh takes issue with that term. The lowest temp he ever got to was 46.6 degrees F. Hugh described a 3 micron layer of turbulent air over the particulate soiling material of an artifact that seems (if I understand correctly) to interfere with just blasting off the particles with air, and that including these tiny tiny “snow” particles allows something with a bit of mass to penetrate through that turbulent layer and knock off the soiling. You’ll need to work systematically from the inside out or one side to another in order to push that loosened material away and not just redeposit it.
When is this useful? Not completely clear yet, it seems like Hugh is exploring that. He says the objects needs to be a hard surface that can momentarily take a drop in surface temperature and a little bit of depression. Your soiling has to be particulate in nature or a low molecular weight hydrocarbon, like perhaps fingerprint oil. Hugh says this technique is not so good for friable surfaces, rough surfaces, bound materials like paint, or oily grime. There’s a learning curve, and you need to control condensation. He showed us before and after images of a bound steel spring and a paper pinbox he had cleaned, as well as a great video of a Robert Morris plastic sculpture (molded cellulose acetate butyrate) with an unidentified but disfiguring surface haze. Yvonne Shashoua helped him with identification of the plastic (she wrote that great conservation of plastics book, didn’t she?)
In the Q&A section, Hugh mentioned that the disfiguring haze might have been migrating plasticizer and there is a theory that if you remove too much plasticizer from a surface it actually can encourage more migration of plasticizers in the object? Did I understand that right? Gosh, plastics are scary, especially these arty ones with the pristine surfaces. In one area, there was a kind of reverse haze pattern kind of like honeycomb from where bubble wrap had been in contact with the surface, which weirdly seemed to suggest the bubbles of the bubble wrap had absorbed the exudate?? Apparently, if you touch the stream it would be cold and dimple your finger but not injure you. His system is gas-fed, not liquid-fed and it sounded like he way saying the liquid-fed systems produce larger sharper crystals of snow. Question about what you might be inhaling during treatment, and Hugh uses clean room pads on the far side of the object to capture particulates. The technology is used for cleaning silicone wafers and lenses for high-end optics. Also, Hugh says that the compressed gas is a byproduct of some other industrial manufacturing process, so it is kind of a green thing, too.
“Examination of an Egyptian Corn Mummy”
Meg Loew Craft, Walters Art Museum
The artifact belongs to a private collector and was loaned for an exhibit in 2004 related the Kunstkammer or “Chamber of Wonders” which seemed rather like the Victorian notion of curiosity corners or cabinets. (I think it might be the same thing?) It came from a 1996 estate sale where the deceased had been to Egypt in the 1960’s and apparently acquired it. Fewer than 100 exist today, although there was apparently some looting in the late 1940’s that led some 400 corn mummies to come onto the market, most of which are no longer in known collections. Museum collections in Houston and Berlin also have corn mummies. Meg reports only 5 necropolis sites have produced them. This one is thought to be Late Period, 685-520BC and the term “corn” does not literally mean corn, but more like some “little hard thing”, usually grain of some sort. They range in date from 2nd half of the 8th century BC to Greco-Roman times, maybe 35-50cm tall, and associated with Osiris and therefore rebirth and fertility of crops. Meg’s materials analysis in this one indicate sycamore fig wood, carbon black pigment, Egyptian Blue pigment, yellow ochre pigment, gold gilding, beeswax, soil, seeds, linen, and traces of some original coating that defied identification but Meg thinks might have been a combo of oils, resins, gums, and maybe bitumen. Malachite was used to make the wax mask green in some areas. The mask was mold made and has fiber inclusions for support. Little canopic figures were found inside also, apparently made of soil with a thin coating of wax. These were seen with CT scanning, which incidentally also allows you to see the tree ring pattern pretty clearly. Dendrochronology might be possible, if only there were a reference database of this kind to compare it to.
“Disrobing: Research and Preventive Conservation of Painted Hide Robes at the Ethnological Museum, National Museums Berlin, Germany.”
By Anne Turner Gunnison, Helene Tello, Peter Bolz, and Nancy Fonicello
Nancy presented this talk because the original presenter was not able to be there, and it was great to have another opportunity to hear her speak (see the tips posting too for her feather cleaning info.) Seven rare and early bison robes in the collection of the Ethnological Museum in Berlin were collected in the 1830’s by Prince Maximillian zu Wied on his travels along the Upper Missouri River. The robes were getting re-housed, which allowed an opportunity for study. One robe that was Piegan (Blackfoot) was investigated in-depth using HPLC and FTIR. It has both painted pigment figural illustrations as well as dyed porcupine quill embroidery. Red colorant showed high levels of mercury, suggesting perhaps vermillion, but in actuality the robe has mercury present as a pesticide in frighteningly high amounts. Bill Holm thought the brown material might be from the root or rhisome of the horsetail. I was most interested to hear this, as I have recently been told that some of the material commonly identified as maidenhair fern stem on Tlingit basketry in Alaska might actually be root of horsetail in some instances, but we all expect to see maidenhair fern stem so no one questions it. Now here is another mention of horsetail root! Nancy is a quillwork expert, and she tells us that not much is published on dye techniques. She experimented with dying quills with fox moss or dock root for the yellow, and bloodroot for the orange-red. If I understand correctly, she gathered and processed these materials herself for a visual comparison. From her slide, the fox moss (with Nancy later told me is probably the same as the wolf moss I am familiar with here in Alaska) and bloodroot sure made comparable colors to those seen on the robe. However, HPLC samples indicated those might not be the dyes used. The idea of a plant called bedstraw was suggested as something that makes a madder-like dye. In the Q&A, someone asked if Nancy thought the analysis could have been flawed. In her experience, fox moss is the only dye material that makes that color yellow. HPLC vs Nancy, I’d place smart money on Nancy. The other interesting thing was that not only was mercury present in ridiculously high amounts, but there were suspicious white crystals on the hair side and a shiny residue was left on the gloves when the object was handled. Suspected DDT was also confirmed by analysis. Quite the toxic robe.
“It Takes Guts”
By Kelly McHugh, Kim Cullen Cobb, Michele Austin-Dennhy, and Landis Smith.
Landis presented the entire paper, as Kelly McHugh could not be there to present the second half. The first half of the presentation was by Landis Smith, about the methodology she designed for the overall project. The second half was read from script written with Kelly’s humor, as she was the intended presenter, but in a way it was a whole different kind of hilarious to hear Landis deliver Kelly’s jokes.
The Anchorage Conservation Project is making the Smithsonian’s holdings more accessible to folks in Alaska through a new wing on the Anchorage Museum working with the National Museum of Natural History’s Arctic Studies Center there. Accessibility is really key, so objects can be requested for closer study and exhibits are designed with mounts to allow easy removal from cases. About 400 artifacts will be loaned from the NMNH and another 200 from the National Museum of the American Indian and the loan periods are up to 12 years. For each object, they are compiling a mountain of data and records for study as well. Many of the artifacts were collected by Edward Nelson, who spoke Yup’ik and whose Yup’ik name translates to “man who collects good-for-nothing things.” Lots of consultants, too…both Native (like skin-sewing experts Chuna McIntyre, Frances Usugan, and Estelle Oozevasenk) and non-Native (like NMNH curator of Arctic Collections Igor Krupnik and the vertebrate zoology folks at NMNH as well as skin artist Fran Reed.)
At this point in the talk, there was a SCREAM from the table behind me and some loud thumps, followed by total commotion among perhaps 6 people. I thought an ambulance would need to be called and someone would have to jump forth to begin CPR, but it turned out to be simply an EXTREMELY large cockroach. Steven Pickman heroically captured the creature in a glass and removed it from the room to great applause and cheers. (This later gave me an excuse to chat with Steven, but that is a tangent I’ll get to in another posting.) Perhaps the cockroach mistook the session for an IPM working group discussion and was spying??
Estelle was the source for extensive information about preparation of gut, and a workshop was done on gut preparation to better understand that material, since identification of the exact animal and the exact organ is difficult and there is only one major conservation reference for this material: Hickman’s “Innerskins/Outerskins.” Linda Lin at the UCLA/Getty program has been investigating gut ID, and so has Amy Tjiong at the NYU program. Both of them contacted me last year, struggling with this ID issue. Of course, I, too, have material in my lab that I would like to identify. Even at this talk and its Q&A period, there was tantalizing and sometimes conflicting information about the nature of gutskin. For example, there is the so-called “summer gut” and “winter gut” issue. Extended exposure of the inflated gut to cold causes a change in its appearance and properties: summer gut is translucent and water beads on its surface for several hours before penetrating, while the white “winter gut” is much more absorbent and has a silky opaque white appearance. Helen Alten had heard that wetting winter gut can cause it to revert back into summer gut, although the Smithsonian folks didn’t find that to be the case. Someone said Julia Fenn, who was not present, apparently suggested once that this “winter gut” is related to freeze drying, and was related to the surface tension of water and how it moves (or does not move) the collagen fibers and causes an air gap…I will need to look into that further. I am most interested in where this is going and who is willing to take this further, as I would like to get involved.