Specimen jackets

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Fossil specimens are found on the surface or at a relatively shallow depth in the ground or rock.  In such a situation the fossils are often cracked or broken.  This can be due to weathering if on the surface, water infiltration if at a shallow depth, root penetration, or expansion and shifting of the enclosing rock as overlying rock is eroded away.  To keep the fossil together, the standard procedure is to encase it in a plaster jacket, like a cast around a broken arm. 

You first expose enough of the fossil's top to tell how big it is and what bone it could be.  Then a few inches outside the fossil you start digging down.  When you have excavated down to below the fossil, based on your previous guess at which the bone it is, you start digging under the bone a little.  What you then have is a pedestal of the fossil and some surrounding rock.  At this point you start making the jacket. 

You make up a mixture of plaster and water in a bucket or tub and then soak strips of burlap in the plaster.  This will form your jacket.  Since plaster sticks to fossil bone fairly tightly, you need to put a layer of something else over the specimen as a separator.  In the past, collectors have used newspapers, paper towels, plastic wrap, garbage bags, aluminum foil, or even toilet paper to act as a separator.  Once the separator is down, then the plaster soaked burlap strips are laid out over the specimen, covering it tightly and completely.  How thick you make the plaster depends on the size of the specimen.  The main thing is you want the plaster thick enough so it doesn't bend when you pick up the finished jacket.  Erring on the side of too thick is preferred.  The burlap and plaster strips are tucked under the pedestal as far as possible and when it is all thick enough you let it dry.  This might be over night. 

Once the jacket is dry and hard it must be turned over.  You carefully remove the jacket and its enclosed fossil and rock from its pedestal base and carefully turn it over.  This is called flipping the jacket.  If all is well, you have an upside down specimen with a thick plaster and burlap shell below and a rock or dirt surface above, with the fossil inside.  The next step is to place a plaster burlap cap on the exposed rock so that the specimen is completely encased in plaster and burlap.  Once this is dry, the jacket may be hauled away without damaging the fossil inside. 

The plaster and burlap can weigh a fair amount, so along with the fossil and rock the jacket can be heavy.  Not to worry, however.  A well made jacket can protect the fossil from quite a bit of rough handling as it is picked up and placed in a truck.  You probably don't want to drop it, however.  The jacket is taken to the museum where it is carefully opened and the fossil inside is cleaned and exposed to the world for the first time since it was buried.

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