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Mar 28

Making a Field Jacket

Posted on March 28, 2018 at 3:41 PM by Bonnie Man

fossil jacketField jackets – burlap and plaster casings used to remove fossils from the field and transport them to the lab – are one of the more iconic images associated with paleontological field work. Paleontologists have been making jackets since the days of John Bell Hatcher (a 19th century fossil hunter who explored the Dinosaur Park quarry in the 1890s), and the process has changed little in the past century.

Every fossil does not need to be jacketed. Small fossils, such as dinosaur teeth, can simply be picked up off the ground, but some larger bones require some extra help. The main purpose of a jacket is to protect the fossil within. Despite being made of rock, fossils are often very fragile, and can splinter away to nothing if you’re not careful. The jacket holds a fossil without much structural integrity together so that it can be removed from the quarry site safely.

When making a jacket, the first step is to find the full extent of the fossil. If you only have part of a bone exposed and try to pull it out, it’s going to break with or without a jacket. Once you are confident the entire fossil is exposed and cleared of loose dirt and debris, you can lay down a buffer layer. The buffer is very important because it prevents the fossil from coming in direct plaster, which is extremely hard to remove. I use damp toilet paper for the buffer, but I’ve seen aluminum foil used as well.

Once the fossil is completely covered by the buffer material, it’s time to start applying plaster bandages. It’s easiest to use pre-made plaster cloth, but if you’re making a large jacket or making many jackets at once it can be more economical to buy burlap and plaster of paris separately. Lay down strips of plaster soaked burlap until you have covered the entire exposed portion of the fossil. The number of layers will depend on the size of the jacket. You want the jacket to be firm and durable, but it doesn’t need to be built like a tank. Keep in mind that somebody is going to have to crack open your jacket later!

The final steps are the most important. Once the plaster dries, you'll need to dig around the fossil so that it is standing on a pedestal of earth. Again, the necessary height of the pedestal depends on the size of the fossil. It's a good idea to add some extra plaster strips around the pedestal for support. Once you are confident that the entire bone is contained within the jacket and pedestal, undercut it as cleanly as possible. The moment of truth comes when you flip the jacket and pedestal over. If you do it right, the jacket will function as a plaster bowl, holding the fossil and its surrounding matrix in place!