Multi-tasking in the UCMP Prep Lab (cont.)

Removing these clods of plaster can be the most challenging part of the job. In the field, making jackets is usually done under less than ideal conditions. There is often little water and few tools—just burlap and plaster, and the occasional big stick added to strengthen the jacket (and all this might take place on the edge of a precipice and/or the unwieldy load has to be carried large distances to transport!). As a result, the jacket is irregular in thickness, the amount of surrounding matrix is unpredictable, and there are few clues as to where the bone is and how close it is to the surface. I use a cast cutter (the same tool that the doctor uses to remove the casts from a broken arm) to slice through the plaster to reach the layer of tissue paper used to wrap the bone. It’s pretty tricky because the thickness of plaster varies, so I go very slowly and peel up bits as I cut along.
Aside from this masonry-type work, I borrow tricks and tools from other professions as well. Once the lid of the field jacket is lifted off, dental tools are ideal. Tiny picks, hooks and needles,
Jane with phytosaur jaw
UCMP’s Senior Preparator, Jane Mason, shows off a fossil phytosaur jaw that’s in the Prep Lab for some repairs. (photo by Colleen Whitney)
  along with a soft brush, help remove minute quantities of sand and rock until you strike paydirt—the fossil. Once a small surface has been revealed, I can then work carefully to expose more bone. Another nifty tool is the mini-sandblaster, although I use sodium bicarbonate (baking soda), dolomite powder, or even crushed walnut shells instead of sand. This tool allows a small stream of abrasive material to remove the over-lying skin of mineralization that often forms on the outer surface of the bone. I also enjoy using the air scribe, a miniature version of the large jackhammer used in road construction. When there is a clean separation between bone and rock, this tool can be used to chip away tiny bits of matrix. The air scribe is very loud, so it is necessary to wear ear protection. Often I use a magnifier to more clearly determine the fossil/matrix interface. Between the ear protection and the magnifier, it is easy to become so engrossed in the work that I feel that I am in another world.
Every fossil is different from every other fossil (even if from the same locality) due to differences in exposure, structure, degree of mineralization, and the variance between individual organisms. The levels of preservation range from the hardness of iron to the softness of talcum powder. Fragile fossils (very soft bone, trace fossils in sand, or something like a snail egg case) need special care during preparation. Thanks to the products of the organic chemist, they can be hardened with plastic varnishes. These products are variable in strength of solution and are totally reversible, so they are ideal for the job.

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