Posted 06 June 2012 - 01:29 PM
Oh, My! The archives of the Forum are not yet available through the "search" function. I hope that's temporary. I did save in my own archives the following from an earlier thread:
"Here is a workable technique for consolidating fossils.
Polyurethane will not give the desired penetration of the fossil. This resin is very difficult to remove. Putting polyurethane on a fossil is usually a bad idea.
I recommend against white glue (polyvinyl acetate) as a consolidant because there are better materials available.* (Normal prep lab dilution of white glue is one part water to two parts glue.) Rarely, a specimen cannot be dried without it crumbling, and white glue is the only reasonable answer. In my experience, white glue is messy and never looks good when the specimen is fully-prepared.
A much better material for bone is a polyvinyl butyral plastic such as Butvar B-76, but that material may be hard to find in small quantities. I have used this plastic, dissolved in acetone, for many types of fossils. (I have used it successfully on Silurian-age shales with brachiopods, for example.) It penetrates well, and in the proper dilution it produces a "damp-looking" finish with no gloss.
Butvar B-76 (but not other Butvar varieties) is also soluble in alcohol. (I assume that is denatured alcohol that you can buy in gallon cans.) I have never tried this solution for consolidation. The alcohol takes considerably longer to boil off the treated specimen.
So, what works best? [most convenient, if you don't have Butvar-76] I recommend a solution of Duco Cement (clear, like model airplane glue) in acetone.
Dilution? Start with a tube of glue dissolved in about five or six ounces of acetone in a glass jar with a metal screw-top. Shake well.
Adjust the dilution with more acetone until, after shaking, the tiniest air bubbles are just slightly retarded in their rise to the surface.
I usually heat specimens with an infra-red lamp to drive off moisture just before dipping the fossil. I do this with all sorts of fossils, and have never had one damaged by the heating. The untreated specimen is always at least as wet at the relative humidity of the air around it, I suppose. (A microwave oven may be as effective, but I've only dried glass beads for my air-abrasive unit.)
Do NOT heat the acetone solution directly. The acetone solution will get warm after dipping a number of heated fossils. You must have good ventilation to deal with the fumes!
I use a long-jawed forceps -- ten-inch tweezers, really -- to dip and/or retreive the fossils from the jar.
Ideally, you would submerge the dry specimen in this consolidant for a brief time (say 15-30 seconds, or until the specimen stops fizzing). Set each wet specimen aside to dry on cardboard (I use beer-flat because that cardboard is absorbant and doesn't readily stick to the fossil).
To avoid pooling of consolidant which may want to drain from a bone, I rotate the bone once or twice in the first minute or two after placing it on the cardboard. This helps avoid a "drip-bead" of consolidant near the lowest point of the bone.
For a specimen too thick to be submerged, you can use a turkey-baster to flood the difficult areas. I treated an adult mammoth tibia that, because of its size, I dried in the Florida sun, then used the baster to pump consolidant into every opening of the bone.
I use a RubberMaid-type cake-pan to hold the consolidant for this soaking step - that plastic seems to be impervious to the acetone. Get 'em at your local dollar-store.
Acetone evaporates very quickly. Replenish the consolidant mixture with a bit of acetone if you are using it on many specimens. Store it in a tightly sealed glass jar. Even if some acetone evaporates away between uses (it always does, it seems), you can reconstitute the solution by replacing the acetone.
Acetone is a nasty solvent. The fumes are explosive. The fumes are toxic. The liquid penetrates the skin-blood barrier. It's best to use gloves. Use in a well-ventilated area.
* Here's what 'oilshale' had to say about white glue:
"Don't get me wrong - Elmer's White glue is a great stuff for glueing wood and can be also great for "hardening" crumbly fossils!
"But I fully agree with Harry's opinion (even so I am a polymer chemist and my job is to develop white glues and other latices....): I would never use a white glue unless the fossil is wet, crumbly and the substrate is porous and can't be dried before consilidation!
"There is no way to remove this white glue once dried (not even with solvent). It will form a dense polymer layer on the surface without penetrating much into the substrate (white glue are tiny polymer particles dispersed in water with a particle size of around 1µm, so the penetration depth won't be much).
"Butvar, a Polyvinyl butyrate (the company I am working in is also producing these polymers, of course different brand names) in this respect is much better (will penetrate better and can easily be removed by solvents).
"I do have a couple of fossil fish which were mistreated by someone else in such a way. Since the substrate was almost nonporous (diatomaceous earth!) and quite soft (and may be also the amount of white glue and concentration used was too high) there is now a thick slightly yellowish polymer film on top. Unfortunately, this is not all: The film shrinks and now peels off (with bones attached to the polymer film of course)!
"Extraordinary claims require extraordinary evidence." --------Carl Sagan