Wooden Artifact Group May 21, 2009
“Waterlogged Wood from the USS Monitor: A New Direction for Research and Collaboration.”
Susanne Grieve, Robert Blanchette, Todd Plaia, and Dave Emerson
Description of the treatment of an Civil War ironclad, sunk in 1862. Collaboration between the US Navy and NOAA on the treatment. Wooden components treated in 1990 are showing sulfur problems similar to those seen on the Swedish warship Vasa. Some parts, like deck fragments, were conserved in the 1980’s and the records are poor. Seem to have been treated with HCl to remove iron and then PEG 400. Crystal growth with a pH of 2 and wood is structurally weak. Untreated wood includes over 150 artifacts from the turret now kept in cold storage. Wood ID, bacteria studies and sulfur analysis are ongoing. Issues with toredo worms and most of the secondary cell walls of the wood are destroyed, leaving mostly primary walls. Everything on the ship seems to be covered in iron corrosion products. They are seeing wood lose more strength if the iron is chelated out. Seems that there is about 4.2% sulfur by weight in the treated wood, and up to 2.5% in the untreated wood. This is compared to 1.5% in the sediment and between 1-3% in the Vasa. Iron is thought to be the catalyst for the sulfur turning into acid. Ammonia gas for neutralization on the Vasa is apparently not working…wood continues to suffer again after a couple of months. The folks treating the Monitor tried Bookkeeper, a magnesium-based product used to deacidify paper. Again,t he wood eventually reverts back to its acidic state. In the Q&A, someone suggested using calcium in order to promote the formation of gypsum, which is very soluble and could be washed out? There was mention of using PEG 400, 1000, and 3350 on a wooden chest, but overall I was disappointed not to hear more details about the PEG treatments, especially the percentages and duration of impregnation. I was also surprised that the understanding of the sulfur source and the mechanism of deterioration didn’t seem to be as advanced as some of the literature already published about the Vasa.
Objects Session May 22, 2009
“Conservation at Kaman Kalehoyuk”
Alice Boccia Paterakis
I was interested in this talk because I took a class there in 1995. It was taught by Glenn Wharton and J. Claire Dean. My husband, conservator Scott Carrlee, worked there on and off from 1992-1997. I don’t think we would recognize the place today. The Japanese Institute for Anatolian Archaeology runs the site, and there are interesting tidbits I thought I’d include here. They plan to re-establish student internships at the site. In 2009 they hope to get a new fume hood and x-ray unit. In 2010, they plan to have a 5-day workshop for archaeologists on spot testing (I think that’s Nancy Odegaard and Scott Carrlee. Hey, maybe I’ll be going to Turkey next summer…) In 2011, they plan a 2-day symposium. Interesting research has been done there, but most of it is published in an obscure journal called “Anatolian Archaeological Studies.” Examples of topics: cyclododecane for lifting of bone. Laramie Hickey Friedman’s work on alkaline sulfite treatment vs non-treatment for iron and then re-examining 8 years later and comparing the specimens on site to those treated and stored at Winterthur. Seemed like the ones at Winterthur were stable and the ones at Kaman were not. They used an RP system by Mitsubishi to seal the metals into bags in 2000. They included silica gel, humidity card, oxygen scavenger, and an oxygen indicator. The RH stayed below 10% for at least 8 years but the oxygen indicator (which may have been the “Ageless Eye”?) turned color, which seemed to indicate some infiltration of oxygen. At the end of the talk, however, Jerry Shiner from Keepsafe Systems Inc (who sells this product) mentioned that the Ageless Eye has a shelf life of about 6 months if kept cold and can spontaneously change color. The thinks the packages were probably OK, and recommends double-bagging to improve the system. Folks in the room really got excited about that, I think. Stavroula Golfomitsou was studying bronzes treated with corrosion inhibitors BTA, AMT, and PMT. Some 220 objects total, both in water and in ethanol. There was one combination that seemed to be head and shoulders above the rest, and I think if I understood right it was published in the 2007 metals conference in Amsterdam, p. 38-43 by Golfomitsou and Merkel. As a resource, there are titles to 20 conservation field notes on a website http://www.jiaa–kaman.org/en/aas/index16.html Hope I got that link right. Alice Paterakis has these as PDFs that you can request.
“Technology as a Tool for Archaeological Research and Artifact Conservation”
Gretchen Anderson and Giovanna Fregni
Discussion of 3-D imaging for enhanced study and less handling of fragile collections. The Science Museum of Minnesota was using the Bodelin Proscope HR, the Leica Stereo Explorer, the Next Engine Desktop 3D Scanner, and CT scans provided by an outside vendor. I really paid attention when I heard Giovanna used to be a jeweler, and is now working on her PhD. I had never heard of a proscope before, and apparently the fancy ones are about $1000 while the basic ones are half that price. They connect to a computer with a USB. The 3-D imaging costs in the $3000 range, which I thought was unbelievably reasonable. Measurements can be embedded right in the image. Also great for getting accurate measurements on things that are really fragile to handle. CT scan on a mummy was able to show the septum had been broken, suggesting the traditional method for removing the contents of the skull during the mummification process and therefore authenticate the mummy. Q&A afterward was focused on various replication techniques to replace old fashioned molding and casting. Some 3-D scans (CAD programs?) can allow a replica to be computer milled out of plastic that is carved away. Some are built up from something like an ink jet that spits plastic. Texas A&M was mentioned as a place where lasers are shot into a tank of liquid resin and the points that the lasers intersect react with the resin to harden it, so you can build up your replica in this way and then just lift it out of the tank. Carlton University apparently had only half an engine, made a replica of the other half with a 3D scanner, flipped it on the computer to make the missing half on a 30D printer, and sent it to a foundry to be cast.
“Connecting Materials Science and Engineering with Archaeological Conservation”
Paul Mardikian, Dr. Stephanie Crette, Dr. Michael Drews, Nestor Gonzales, Johanna Rivero, and Claire Tindal.
Discussion of the treatment approaches to the treatment of H.L. Hunley at the Clemson Conservation Center in South Carolina after its recovery in 2000. Human remains were reburied in 2004, and Clemson University took over the project from the Navy in 2007. The Clemson Conservation Center seems to be actually in the School of Materials Science and Engineering at Clemson? They seem to have a staff of 10 or 12 people. Interesting research includes addressing the problem of chloride salts in the layer between the core iron and the surface corrosion (did he call that surface layer “Graphetization?”) Subcritical fluids at a high temperature under pressure seem to do a lot to diffuse out the chlorides in that interface, where they can be up to 10%. Reduction of surface tension and improved solubility means the diffusion happens fast, like a matter of days. There is a constant flow of solution (sodium hydroxide) and it is measured for chlorides on its way out of the 40L tank. What level of chlorides? They used to aim for under 10ppm, but now they can get below 0.5ppm in less than a week! This is still in its infancy, however, very much still in the experimental stage with small items. There was also talk of the importance of identifying corrosion products before treatment and after treatment in order to assess if stabilization is successful.
Supercritical CO2 is another approach used for certain problems such as waterlogged cork. Water exerts violent forces on fragile cells when water evaporates because of its high surface tension. Liquid CO2 has no surface tension, from what I heard at this talk, so if you replace water with a solvent and then that solvent with CO2, you can avoid the surface tension issue. Methanol and liquid CO2 mix well at a certain temperature and pressure.
Also mentioned 3D scanning for items in order to get really accurate readings to measure shrinkage. Hard to use caliper accurately on small artifacts, and using pins is only practical for larger things like ships timbers.
Paul Mardikian was an engaging speaker and at the end he kind of waxed poetic about the possibility of mass treatment for archaeological iron being a reality in the future. He feared it might end up a mirage, but was really starting to have hope. I also smiled when he described an upcoming deadline for abstracts if people want to present papers at the Metals Conference in Charleston, South Carolina in October 2010. As he put it, if your abstract is good, there can be an extension beyond the June 1 deadline. But if your abstract is not good, then the deadline is firm.