(Published in "Tips and Trips", Vol. XXXI/5, May 2002, Page 6.)
Paleo preparation to make fossils look nice is usually the result of skill acquired with lots of practice working with fossils. The basic techniques are fairly simple and are well described in various books or pamphlets on the subject, many of which can be read in public or school libraries. These techniques have changed little over a couple hundred years. They consist of scrapping off matrix, grinding off matrix, dissolving off matrix and stabilizing or strengthening weak fossil material. The tools to do this include hand-held scrappers, picks, hand-held grinders (I use a Dremel), air-abrasive units, water guns, acids for dissolving soluble matrix, etc.
Stabilizing is more specialized, but can be done with resins, which should be thinned before use. Another consideration is that in many situations, areas of the fossil already exposed during preparation should be protected from further attack by coating with a temporary protective layer. Usually, to do all this properly, you should be using a binocular microscope to check the fine detail as the work progresses. These are techniques that can be learned easily by some practice, and often practice is required to judge what will work with the type of rock and fossil you want to work on.
Teaching yourself with basic tools is really the best way to learn preparation. Apart from the basic methods, three other factors are very important:
- willingness to work slowly and carefully
- evaluating the condition of the fossil, and
- an understanding of what is possible in removing the matrix rock.
The second factor is a critical step: deciding if preparation will really improve the fossil in hand. This clearly requires some experience, which can be acquired by trying to do some preparation and accepting some failures. Many, many fossils are not very well preserved and are suitable for garden rock, but not display material. Preparation will not change that condition.
Then, there is the matter of knowing the composition of the matrix and if, or how, it can be removed without destroying the fossils. For fossils like large bones and completely silicified shells, simple techniques may work well, but for a fossil very similar in composition or hardness to the matrix, grinding to remove matrix may be the only option. In this case, preparation may be impractical or will result in considerable damage to the fossil if not done in very small steps. This is especially true when using an air-abrasive unit. A water gun is better, if the matrix is moderately soft and the shell hard. If you have little experience doing preparation, a water gun is a better tool than an air-abrasive unit for softer matrix. If you want to remove hard limestone, a hand-held grinder with carbide bits (diamond if you can afford it, but these bits are usually very small and too fragile) is the best tool. In all cases, clean the surface frequently and check to locate the precise boundary of the fossil. This equipment is not very expensive, except the binocular microscope and the air-abrasive unit. The binocular microscope is the most important item for really good results, but you may not need it if the preparation can be done in a rough manner.
Tom, I agree with all you said... and might add one more thing. It is absolutely necessary to be as familiar as possible with the type of specimen you want to prep. I mean as to the size, shape, orientation in the matrix, number of appendages, etc.. If you know these things also, then prepping the specimen to present the way you want it to when finished is much easier. Try to cut the matrix to the size you want it before doing any work on the fossil, this way the specimen is protected from the effects of sawing, etc.. After sizing the matrix, for mudstones, I would recommend using grinders with diamond tips as Tom suggested to get the greater part of the matrix removed. Then begin the exposing of the specimen itself with scrapers of various shapes and sizes. Keep in mind, the round edge of a pick will remove matrix just as quickly as the sharp edge of a blade, and will not scar the specimen. I generally complete the prep with a quick airbrushing when warranted.
Good luck... C2
Carl J. Cook
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