Looking at one of your other questions, the one called "Fossil Conservation", I can see a paper attached by Marco Cherin, that I was just about to recommend.

That paper describes how Paraloid B72 can be used for fossil preservation. This acrylic resin is not affected by changes of temperature, and is not soluble in water (it dissolves in organic solvents, such as ethanol or acetone).

I think this substance could be very useful in the particular case presented by you, because it can be used in two ways: it impregnates the pores (if the fossilized wood still has pores), and it can also be used to coat the wood.

I think you should read that paper, and conduct some tests on materials similar to what you want to preserve, to make sure Paraloid B72 does the trick.

We have solved this in protection of the specimen from rain and water comming to the specimen from the ground. If the specime is in dry condition you can try to apply various commercionally avaialble conservants.

The conditions you describe are not extreme, no frost and enough rainfall that you would have no big problem with solution of free salt following heating by insolation. Problems might appear, if the wood is not completly silified, or you have high or intermediate content of iron sulfides decaying under such climatic conditions.

Usage of one of the Paraloid products used for conservation of less fossilized or heavily weathered material of wood, bone or invertebrate fossils may be contraproductive and sealing the material may result in decay due to inappropriate microclimatic conditions. Also you might get problems if clay minerals are involved.

If you have a solid trunk of a tree, not important to science and only used for display function, well silified and without cracks, you did not need a special conservation. If one of this points is unfounded, don't leave the wood in situ under open air conditions.

Thank you for your answers and your interest. Let me provide some more information and some of my thoughts...

We are not sure about the exact RH and T levels as these have not been recorded yet in detail. These are readings taken from the internet, and the data they used comes from a metereological station a few km away. We are planning to put dataloggers and meteorological stations at every fossil site soon to see what the real conditions and the micro-climate around each fossil are.

I believe we should expect important fluctuations. I took a few readings during my last reading to the site. To give you an example, On December 31st at noon, RH was about 42%. Eight hours later it was 87%.

The fossils are in Thailand, so there is very heavy rain. The butresses of the trees have actually dissapeared due to heavy rain and flooding.

Analysis of the material has been planned, so at the moment I can not tell you the exact percentage of SiO2. The fossil is quite porous and brittle though...

I will not risk using any materials without testing and I will avoid plasticizing the fossils. For me, reversibulity is very important. And so are the fossils. One of them is the longest fossilised tree trunk in the world and is expected to enter the Guiness book of records soon.

I would not use Paraloids..... Paraloids turn to turn white in contact with water. Put some Paraloid solution in a beaker and then add water and see what will happen. I had tried Paraloids in another petrified forest in the past and I was not happy with the results. Paraloids only work for filling cracks. The whitening effect is minimised with the addition of more materials in the solution. However, the fossil must be protected by a water repellent afterwards. And then, it is difficult to control moisture rising from the ground. The fossil must be able to "breathe", otherwise, the results will be worse.

In the past, as an adhesive, I used Paraloid B67 instead of B72, because I needed a higher glass transition temperature. Fossils store quite an amount of heat in their bodies, the same way that a car does when parked outside on a sunny day... We used to joke with my team about frying eggs on the fossil surfaces. In several occasions, pieces adhered together had fallen apart just a week later, because Paraloid B72 had melted because of the temperature of the fossil surface.

If you are interested about the techniques I have used in the past, I have summarised them in a paper entitled "Conserving the Lesvos Petrified Forest" (Kyriazi and Zouros 2008).

However, I want to test more materials for the petrified forest I am working on now... I would not feel confident suggesting the same materials I had used in Northen Greece.... Don't forget, weather in Greece is quite different than the weather in Thailand. And so is the budget...

I think I know the site you are writting about from one conforence presentation. I remember the trunks are dug in soil and some (one?) covered by a roof. The major problem there is moisture comming from the ground. Also the trunks are in excavated ridges, which are probably filled with water during rainy season. First I think the ridges require drainage, but even so, it would be difficult to keep them dry in such conditions.

Best preservation of the trunks is to transvere them to some dry conditons (light timber building or so...) or to leave them in the soil...

I have no direct experience with conservation of fossils like that in situ, the more to leave it at the site - you seem to be quite skilled in this, just in another conditions. In fact, if you dried it too much, it would most likely collapse - by the way, you should for first know, if and how much of the original wood remained non-silicified, how much of clay is inside the structure and how it is distributed. An alternative to paraloid, maybe justified in the conditions, is application of silicates which are used in conservation of buildings and so on, however I have no experience with.

It would be needed to know the local conditions better, but once uncovered, the trunks after re-burial could suffer due to water accumulation or increased flow during heavier rains.... As you stated above, there is high danger of creating zones or enclosures of different microclimate by the paraloid impregnation, which could cause further cracking due to increased tension...the same problem would arise with another acrylates and all the resins even though you would begin with very thin solutions.

It is very uneasy to give any good, safe advice in this case, you see :) ...the more, there is probably not a lot time to test a lot of eventualities for longer period... For first I would suggest to cover/shelter the trunks to minimize evaporation and drainage the location to get more time...

Ok, I see, more of the suggestions I am giving are stated above. I am sorry for the repetition...

I used to use Rhodorsil RC 70 and Rhodorsil RC 90 as water repellents in the Lesvos Petrified Forest. Now I am looking for more materials to test.

... you may contact the Rhone-Poulenc, a french chemical company, about etil-silicato RC70 or RC80

Rhodorsil RC70, Rhodorsil RC80 and Rhodorsil RC90 are ethyl silicates. They are either produced by Rhodia, or by Rhone-Poulenc or other companies. Sometimes their name is also Bluesil RC70 etc. I have used them in many occasions, both on fossils and on archaeological sites. They are definately some of the materials I am going to test. I am however looking for more materials to test, bith consolidants as well as adhesives.

Jiří, yes, one of the fossils, the longest one, measuring 69 meters is covered by a roof, but still water comes in because of the wind. We are thinking of ways to fix the problem. Another smaller roof has been put over the buttress of another fossil. One of the things we need to do as soon as possible is to cover all of the fossils, and solve the problem of water accumulating around them. We are trying to get some money from the local government.

Meanwhile, I am investigating on the physico-chemical structure of the fossils to see what its structure and properties are.

Hi Evangelia,

Have you thought about using carbowax/polyethylene glycol.

I've pasted an extract from google books relating to the preservation of the timbers from the Mary Rose (a sixtenth century ship recovered off the english coast).

Alternatively just google carbowax and Mary Rose.

The text suggests that the RH had to be maintained at a high level which wouldn't be difficult for at least part of the year!

http://books.google.co.uk/books?id=gAORAgAAQBAJ&pg=PA145&lpg=PA145&dq=mary+rose+carbowax&source=bl&ots=t6OM3I4pVZ&sig=NtSsy7sWgcIO9IXyplNu0rvUUzs&hl=en&sa=X&ei=_pggU-v5BvHQ7AbelYDwDg&ved=0CEoQ6AEwAw#v=onepage&q=mary%20rose%20carbowax&f=false

Hello Scott!

The fossils we are working on are not wood anymore. PEG is used for archaeological wood. In this case we are dealing with silicon dioxide as the main material.

Hi Evangelia,

We meet at the PCU at the Natural History Museum in London but I'm now work freelance. I suggested carbo wax as is water soluble and therefore reversible, can be transported into the specimen (impreganated). I use it regularly for conservation and preparation especially preparation supports field jackets and as a consolidant. Maybe other professioanls having experience of using it on fossil and sub fossil specimens. Will the specimens start to dry out once you've solved the rain/water ingress problem thereby facilitating crystal growth in your "silica" specimens.

If you need an adhesive would lime motar meet your needs. It can be removed if needs be and continues to function even when wet/saturated as the water can pass freely into it unlike the majority of plastic based adhesives and consolidants.

Both materials would avoid "plastisizing" the specimens.

Dear Evangelia Kyriazi

In my opinion and from my experience any kind of consolidation agents under the conditions you described are very problematic because of the of the water repellent effect which is never acting in only one direction. 

Rising humidity fom the ground with additional soluble salts may cause severe damage as well as thermic induced dilatation without accompanying procedures like blocking capillarity by excavating the fossilized trees and dissociating them from the wet ground.

The impact of every kind of stone consolidant (PMMA, silica ester, etc.) on the physical properties, especially on porosity characteristic always are serious, therefore you should test different consolidants on small samples in the laboratory or make some experiments on small pieces in situ under natural conditions before you start a comprehensive consolidation campaign.

Best regards

Andreas

Hi, as the material is silica based, I would think of any organosilicate consolidants (e.g. silicic acid esters and alkoxysilanes) which are a very good choice for silica-based consolidants. The consolidation action of organisilicates is formed through the formation of a reticular structurr similar to that of silica, making these conslidatints well-suited for silica-based materials due to their high compatibility. The most popular ones are TEOS and MTMOS. And nowadays, there are many nano-alkoxysilanes (e.g. UCAD).

I would have a look at this:

https://www.google.com/search?q=wheeler+2008+alkoxysilanes&ie=utf-8&oe=utf-8&client=firefox-b-ab

Definetely no B-72.

Thank you Jorge. Can you suggest any links or papers?

Thank you Evangelina. I know there is a new nano siloxane product called UCAD-2o that it is becoming very famous for silicate-based stones. I attach the first publication they published where it explains the composition and properties:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.858.739&rep=rep1&type=pdf

I read that it has also been succesfully tested in many quartz-based stones many times, you can find papers about it at the developers publications:

María J. Mosquera

I hope this can help you a little bit, regards, Jorge

I think this question is highly dependant on the material properties of the fossilized wood in question; and the environment it is situated. Wood can range from perfect silicification, vitreous blocks of no porosity like Petrified Forest in Arizona, Near Perfect Silicification like Florissant, where we see unique patterns of stone deterioration like fibrous disintegrations or ring-shake, or wood that is 20 million+ years old, lacking cellulose, but just lignin in the Canadian arctic. Its a big spectrum. At Florissant Jennifer Young noticed that ethyl silicates (TEOS) created a white haze on the surface of the rocks she trialled, this was likely because of the relative impermeability of that specific material.

Excellent answer Evan. Thank you for your contribution.

I had the same problem with ethyl silicates at the Lesvos Petrified Forest.

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