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Prep of Green River Fish at Fossil Butte National Monument


Sagebrush Steve

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I just got back from a week-long trip that included a stop to dig Green River fish at the American Fossil Quarry outside of Kemmerer, Wyoming.  That was a successful venture and I will post a separate entry showing some of my finds once I get them unpacked.  While I was there, I stopped in at the nearby Fossil Butte National Monument.  In the visitor center, one of the rangers was doing a demo of prepping a Green River fish (a Diplomystus from the 18" layer they got from one of the commercial quarries).   I didn't take any photos but I did ask a lot of questions.  Before I share his answers, you might want to take a look at this video from the Fossil Butte National Monument website.  It shows how they prep the fish using an air scribe and air abrasive.  But be warned that what I learned isn't exactly the same as what is shown in the video here:

 

https://www.nps.gov/media/video/view.htm?id=9BD712EE-1DD8-B71B-0B88EC525E86D328

 

The setup I saw was the same as in the video.  It looked like a home-made blast cabinet with a sheet of acrylic plastic on top, held on by blue painters tape.  It was connected to a good dust collector.  The microscope, as in the video, looked like a Leica-Wild M8 stereomicroscope with a video camera on top and an offset binocular viewing head.  This is a top-of-the-line unit that probably cost somewhere between $7,000 to $10,000 (sadly, this model microscope is no longer manufactured, but you can pick them up on the used market if you have enough money).  The microscope seemed to be fixed in the center of the blast cabinet, you move the specimen around under it. I didn't learn the make of the air scribe tool he was using, he said it was a specially modified one with a large rubber sheath that reduced the vibration transmitted to his hands.  For the air abrasive, they had two Crystal Mark Swam Blasters model EV-2.  One of them, set off to the side and not being used, was labeled "Dolomite."  I asked him what abrasive he was using and he said iron powder.  I was surprised because I thought that would be much too hard on these fossils, but as I watched on the screen it did a great job of removing the matrix without damaging the fossil.  I probed some more and he said that while the machine could be set to go up to 80 psi, he had it set to 13.3 psi.  There is also a setting for powder flow that can be set between 1 and 10.  He had it set to 6, and when he is doing delicate work on the fins, turns it down to 2 or 3.  He also said the nozzle was specially modified to be smaller in diameter.

 

I was pretty impressed with the quality of his work and am inspired to make my own blast cabinet similar to theirs (but without the high-priced microscope).  I thought everyone might like to know what works for this facility even though it's different from what is usually recommended here on this forum.

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Very interesting. Thanks for sharing @Sagebrush Steve. The traditional thought process is to use an abrasive that is softer than the bones to reduce possible damage (recent studies show that even using abrasive damages the specimen microscopically). 

 

Clearly, they are running at such a low pressure to mitigate damage caused by the hardness of the iron powder. The funny thing to me is that soda and dolomite are both cheaper than iron powder typically, and at higher pressures probably work as fast as the iron.

 

One benefit is that this reduces the likelihood of blowing bones off with the pressure of the abrasive. 

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4 hours ago, RJB said:

What Ptychoduso4 said.  With Kris here I dont really have to type anything.  :)

 

RB

Don’t discount the 100 years of prepping experience you have. :P

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  • 2 weeks later...

Iron is not as agressive as dolomite (although higher on mohs scale), soda on the other hand is the softests of the 3 mediums, so it works best to preserve details as long as there is only a thin cover of limestone and since this limestone is very soft and bones hard soda is a great medium for GRF, and this type of prep very easy, just takes time. But in the end a lot depends on your setup and settings... Great post!

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