Something genuinely practical for the ‘Practical Palaeontology’ section this time out, making palaeontological jackets. For those who don’t know, a ‘jacket’ is the name given to the bundle of plaster (or other materials) used to wrap up specimens to transport them. Whenever you see photos of palaeontologists working in the filed they are nearly always accompanied by large white blocks of jackets made up to protect the fossils that have been excavated to get them back to the lab safely. They can be time consuming and awkward to make and there is a certain art to their construction. I thought it would be useful for potential palaeontologists to have an idea of how to make these and perhaps be of interest to more general readers.
The general point of a jacket is to protect a specimen from its journey from the field site where it was found to the lab to be prepared free of the rock in which it lies. You don’t always need to make them (there’s no point for small pieces that can just be put in a safe box), but they are a very common feature of palaeontology. While fossils may be made of rock and buried in rock, they can be phenomenally fragile and a journey of dozens or even hundreds of miles across country in a 4×4 in unlikely to be the best way of keeping them in one good piece, hence the jacket. The principle really is to take out enough rock to encase the whole specimen and keep it secure, but not take out so much that you can’t shift it. By binding the whole piece tightly with a touch outer coating any breaks can’t shift against each other and the specimen gets some physical protection from any bumps and bashes.
The photos here are all from a number of jackets we made while recently in Henan which is why they’ll change shape and size in the photos as we go through the procedure, but the point is what to do rather than what we did it on. I’d also note that there are of course alternative ways of doing things that I list here and certain parts can be done at different times without really affecting the method, so this is hardly a gospel account of jacket building.
First off you need to clean the surface out and work out how big the specimens is (and where it ends if it’s still largely covered) and thus how big the jacket will be. You may have to deliberately break the specimen into several chunks if it’s just too big so having a good idea of what you have and where and how it lies is pretty important.
Now you can clean up the surface and start digging around the specimen to make a trench. Again the balance is between leaving enough rock to protect the specimen and keeping it light and simple. The trench will also be the start of how you complete the jacket so it’ll have to be to a sufficient depth to actually take the whole block out, though to being with it can be quite shallow. You also have to watch out for stray bits of specimen, or even a second one that might be lurking nearby. You can see in the photo above that we end up with two specimens close together as making the trench for the first turned up a second that then had to be taken out in a separate jacket.
One you have a reasonable trench you can cover any exposed bone in wet tissue paper (some people also use aluminium foil or other materials). This is to protect the bone from being stuck to the plaster. This can be removed later on but it’s tricky to do and takes time when a thin layer of something easily removed can be added in quickly. You should of course have added some consolidating agent or glue to the bones and / or rock during your initial investigation but might need some more now before the paper goes on. Any little spaces or holes should be packed solid with paper to keep things nice and tight when the plaster goes on and prevent things shaking or breaking later on.
Now the first layer of plaster can go on. This is usually either as plaster bandages such as hospitals use to make casts, or as burlap sacking dipped in plaster of paris. Add the layers on so that the material overlaps and runs in perpendicular layers for strength. Make sure the stuff goes on tightly and does not leave any spaces between the plaster and the rock, you want the whole thing to bind on tightly. The bigger the eventual jacket the more layers you might need, but you can always add more layer on if necessary. If they jacket is very small you can do the whole thing in one go in your hands as you just wrap the piece up with one long strip of bandage (like the one shown at the top of the page).
You can now make the trench somewhat deeper and begin to undercut the specimen. You’ll want to leave enough rock to keep it well supported but clear out the edges as far as possible so it can be removed safely. If the trench is deep then you can add a wrapping layer that goes around the specimen to fill the space in, support the sides and help bind the top layer on better.
You can now undercut things further with the ultimate aim of collapsing the pedestal of rock that supports the half-made jacket. You still need to be careful but by now you should be clear of any other fossils in the surrounding rock and the whole thing should be pretty stable and secure. Once you are through, you can flip the jacket over to get to the underside.
At least some of the pedestal has probably remained attached and this can now be cleared off to make the whole package lighter and allow the layers to go together better. You can now plaster the base making sure it overlaps firmly with the middle or top layer as appropriate to keep the whole thing solid and strong.
Next up, label the jacket. It’s no good getting it back and not knowing what’s in there, especially if you don’t return to it for a few years. Make sure the labelling is clear and takes into account orientation (is that 669W, or M699?) and is visible on most sides so you don’t have to turn it round or flip it over to find the field number. Finally make sure you mark the top – you don’t want the preparator to have to go through two feet of rock when the specimen is actually exposed free on the opposite side.
Finally you can transport your jacket in relative safety though as you can see here, mechanical help is not always available and even a medium sized one like this can be in the hundreds of kilos. For big jackets, if available, you can actually bind ropes or pieces of wood to the plaster to provide carrying handles which can help considerably.
Hopefully this has provided a lesson for various budding palaeontologists. As ever, helpful comments and tips from experienced field-workers are welcomed. I know I don’t have much experience in this kind of thing as yet (though it has grown exponentially in recent months and with another big summer ahead it will jump forwards again) but I’m pretty sure that covers it all. Certainly I have yet to build any huge jackets and have only seen the enormous ton+ ones that some crews build when then have the facilities, though I’m not sure the technique is any different bar the sheer scale and need for extra strength.