degreasing fish skeletons

San Diego Natural History Museum libsdnhm at CLASS.ORG
Thu Oct 31 10:15:37 CST 1996


It's a good idea to stop using 1,1,1-trichloroethane for human health and
safety reasons. You may even be using it illegally--I know several people
who have found the restrictions on its use and disposal to be quite
draconian.

The first question to consider is why you are degreasing bones, and if
you are able to stop the process before you do irreversible structural
damage. In other words, are the bones bleeding lipids into their storage
environment (which should be dealt with), or are they just not white
enough for someone's taste?

The urge to make all bones bright white is a misplaced exhibits esthetic
that has somehow found its way into collections management, to the
detriment of many skeletal specimens. The problem is that there are
several types of lipid compounds in bones, some of which oxidize readily
and are readily removed, others of which are part of the bone's
structural integrity and should not be removed. Soaks in caustic chemical
solutions destroy both of these groups and yield a white, greaseless, and
often brittle or fragile bone. Fish, sea turtle, and cetacean bones are
the trickiest to manage along these lines, as they have lots of these
compounds.

You can remove unpleasant oxidizing compounds at the surface by swabbing
with regular 70% ethanol. For robust bones that are truly greasy, you can
soak them briefly in ethanol. You may have to do this more than once in
preparation. I don't recommend chlorine bleach or ammonia compounds: they
are quite harsh in their effects on the bone and can destroy very fine
bones quickly. (Yes, that is the voice of sad experience talking.)

Whatever you do, do *not* use the commercial enzyme pre-soak detergents
recommended in a _Copeia_ article several years ago. A colleague and I
published a paper in _Collection Forum_ on the extremely distressing
long-term effects of this on a collection of what should have been fish
bones but were in fact powder. The enzyme was never denatured and
destroyed *all* the organic fraction of the bone. It was a very effective,
if sobering, demonstration of why you don't want to de-grease a bone
completely (as well as why you really should understand the chemistry of
what you are doing to a specimen before you do it).

David Von Endt at the Conservation Analytical Lab (Smithsonian) is part
of a research project investigating the use of very precisely measured
and timed enzyme treatments to de-flesh and de-grease bones without
damaging them structurally. He gave a presentation of preliminary results
at the 1996 meeting of the Society for the Preservation of Natural
History Collections, and I hope that there will be more information at
SPNHC in 1997.

For now, I would take into consideration the degree of surface grease,
the robustness or delicacy of the bones, and their use (are they to be
used as articulated or disarticulated specimens?). There is no one
approach that will work for every condition, and there is a lot of oral
history and ancestor worship out there that has resulted in the use of
untested methods that look good at first but which turn out to have
devastating long-term effects.

Good luck. Stay in touch.

Sally Shelton
Director, Collections Care and Conservation
President-Elect, SPNHC
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|                 San Diego Natural History Museum                      |
|                          P. O. Box 1390                               |
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On Thu, 31 Oct 1996, Scott Schaefer wrote:

> To the bone folks,
>
> AMNH has been using trichloroethylene to de-grease fish skeletons. It
> has worked very well with little detrimental effect on the specimens,
> however, is now becoming hard to obtain and quite costly.
>
> Can anyone recommend an alternative chemical?
>
> --
> Scott A. Schaefer                                schaefer at amnh.org
> Associate Curator
> Dept. of Ichthyology                           voice: 212-769-5652
> American Museum of Natural History             fax:   212-769-5642
> Central Park West @ 79th Street
> New York, NY 10024-5192 U.S.A.
>




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