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
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.