Monday, August 25, 2014

Making a Archival Cradle for Bernie's skull

I just got back from a two week fossil hunting trip including a week digging at the famous Como Bluff in Wyoming. I'll have more to say about that later. First, here's what I did immediately before the trip.

Part of preparing a fossil is preparing long-term storage for it. Fossils will badly deteriorate if rattled around loose in a drawer, many will break under their own weight, and all will get scratched if rubbed by other fossils. Bernie's skull will have to be protected for the long term (100+ years) by a rugged cradle of some sort.  I have followed a procedure developed by the Peabody Museum at Yale to make custom supportive cradles to protect it.

A link to the Society of Vertebrae Paleontology's Preparer's resources  can be found here:
 Resources for Preparers

And a specific link to the cradle technique is found here:
A Review of Vertebrate Fossil Support (and storage) Systems at the Yale Peabody Museum of Natural History

Using this technique, first I cut a piece of 3/4 inch plywood in an oversized outline of the skull. The edges are beveled to allow for easy pickup of the cradle and fossil. The oversized outline prevents the fossil from bumping into adjacent fossils (if they have similar cradles). The drywall screws projecting up into the plaster will hold it to the plywood since plaster and wood would otherwise separate in time.
I rolled out a piece of clay to act as the substitute for the eventual padding layer. I made the clay approximately 3 mm (1/8 inch) thick . 

Then I covered the skull with a separation layer. You can use thin cling wrap, but I chose aluminum foil as it would bridge the gaps in the skull nicely. 

Then I covered the aluminum foil with the clay where the future padding will go. This goes on the underside of the skull when it is on the cradle. For Bernie, I had to be careful that the cradle would not capture the fossils and keep it from being removed from the cradle. (It could not be re-entrant)

Here's the cradle base with the clay-wrapped skull. 

Then I put an additional layer of aluminum foil over the clay to prevent it from sticking to the plaster. 
 After mixing the plaster quickly, I put a large amount on the plywood, inserted the skull, and smoothed the outer edges. The plaster set quickly and I did this in two applications to give myself enough time. After hardening a few minuted I smoothed the outsides and trimmed the upper edge to be about 3 mm (1/8 inch) thick.

 Here is the cradle after the plaster has set and the aluminum foil and clay have been removed. For the moment I am using a layer of no-slip padding to keep the skull off the plaster. Eventually I'll have to get a longer-lasting plastic foam, probably made of Polyethylene. However, since the cradle is deep, I may decide to not glue the padding to the plaster and keep a replaceable foam padding.
 And here's the other side. It keeps the teeth up in the air so nothing touches them.
Hopefully this will last 100+ years, but I won't be around to see that. 
Sincerely, Greg Carr

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