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:
- Compile physical and chemical properties through literature search/ experiment
- Swelling/sorption capacity (easier to test on sound wood)
- Experiment on test and archaeological samples
- Potential degradation
- 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.
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
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.