Amy Davidson American Museum of Natural History Tips for Unjacketing Amy Davidson American Museum of Natural History

Unjacketing Problems

Jacketing in the field often involves a large, enthusiastic crew Jacketing in the field often involves a large, enthusiastic crew. Unfortunately with this many people working it can be very difficult to control the quality of the jacket. Paleontologists may have years of experience in jacketing, but they may have no experience in unjacketing and can be unaware of the challenges that over enthusiastic jacketing may create back in the lab. Ultimately a jacket cannot be considered successful unless it can be opened without damaging the specimen within.

three inches thick! This is a typical problem- this very fragile specimen in sandy matrix has an enormously thick layer of plaster and burlap laid almost directly on the bone surface. There is just a whisper of toilet paper between.

an undercut Another typical problem is undercuts that lock the jacket into the specimen. This was a booby trap for anyone trying to open this jacket without pulling up the surface.

toilet paper undercut stuck to plaster too thick! toilet paper undercut stuck to plaster This smaller jacket of plaster bandage had two booby traps: On the right you can see that the bottom half of the jacket is way too thick , especially on the left edge. On the left the wadded toilet paper “separator” that was tamped wet onto the bone surface has dried very hard and stuck to the plaster. This defeats the purpose of the paper. Instead of separating the jacket it has becomes part of it and caused it to grab the surface of the specimen. If a jacket like this is not opened very cautiously the specimen can be accidentally sawn into or the surface ripped up with the plaster.

an undercut can rip up the specimen This jacket was opened carelessly like a jack-o-lantern, by sawing around the top edge and popping off the top. Unfortunately some of the specimen has popped off with the “lid”. an undercut can rip up the specimen

Here a similar attempt to “pop the lid” by making a deep, blind cut around the top edge has damaged the specimen. This jacket was not well made. It is very thick and not well separated from the bone. a saw cut into the bone

Tips to avoid problems

Unless you know that a jacket has been well made and designed for easy opening (like this one), it is always safer to assume that there might be problems.

The first thing you want to do is get some sense of the thickness without cutting into the specimen. The best way to do this is to carefully open up a V-shaped cut . Unlike a straight cut, the V-shape will help you peer into the jacket and find the surface without damaging it. Take your time and work in stages.

After the thickness of the plaster has been ascertained and any separating layers located, the cut is enlarged into a small window.

The window is gradually further enlarged The window is gradually further enlarged. In this manner there is no risk of cutting into or ripping up the specimen because you can see what you are doing.

Here is another example of starting by opening a small window…

…which is gradually chewed away, enlarged and trimmed back until the specimen is found.

Small jackets of plaster bandage do not have to be very thick to be strong. A well made plaster bandage jacket is even, tight and thin enough to peel away. In this case the bandage is adequately separated from the specimen by a layer of toilet paper but it is even better to have an additional separator of aluminum foil or plastic wrap on top of the paper to prevent it sticking to the plaster (see next slide).

Aluminum foil is an excellent way to separate the plaster bandage from the toilet paper. You can see here that I had to hold the foil in place with chunks of matrix until I could work the plaster bandage over it.

This little protoceratops jacket was a breeze to peel away with a thin, even thickness and three layers of separation between plaster bandage, aluminum foil, toilet paper and the specimen.

And here are the rewards of a careful jacketing and unjacketing- a beautiful specimen safely collected.