Polyurethane and modern human bones

Tom Bodkin <hominid [at] email__msn__com> writes

>... Nevertheless, in the interest of preserving such a
>hard-to-come-by comparative specimen I chose a spray-on clear
>polyurethane.  My reasoning was because of the hardness achieved,
>the ease of application (too fragile to paint bone by bone), and the
>transparency of the coat.  I did not, however, spray all of the
>bones, leaving the lower long bones uncoated in case future DNA
>tests ever arise.  My questions to this listserv are:  1) are there
>are any long term negative interactions with the conservation method
>I have chosen, and 2) is there anything better?

For all the reasons you have so rightly identified (interference
with DNA and other analyses now and in the future, etc.), you have
to be very careful of any adhesive or consolidant you use with any
biological specimens. With such a fragile skeleton, it's a delicate
balancing act between preservation of the morphology and
preservation of the pristine sample. My guess is that you don't have
the latter absolutely (very few of us do, as the methods for
skeletal preparation traditionally emphasize maintenance of
morphology over maintenance of biochemical "cleanness").

Before you proceed, you have to decide what, if any, fraction of the
material might be used for destructive sampling and testing. Once
you decide this (quite an issue in itself), make sure you have that
decision in writing attached somehow to the specimen record and
files. If you have a relatively uncontaminated part of the skeleton
*and* you have decided that some destructive work is acceptable on
this, don't go any further with adhesion or consolidation with this
part of the skeleton. I would personally seal this part in some kind
of microenvironmental enclosure. You want to minimize or eliminate
all sources of contamination for such a sample, including human hand
sweat and oil, storage system offgassing, air pollutants, etc. A
sealed enclosure will also buy you a little time if the unthinkable
happens (as it does) and the collection is soaked or flooded.
Naturally, you'll want to keep this is a UV-free environment.

If the skeleton is not to be used for any kind of biochemical work
(whether because or rareness, fragility, irreplaceability, ethical
and political implications, etc.), you can look at the problem
slightly differently. If the specimen is basically stable, don't go
any further with consolidation: worry more about safe padded storage
that will provide some isolation from vibration. In other words,
don't consolidate first. Many polymers I've worked with in
biological and geological conservation have aging characteristics
that can affect the appearance and even (especially with such
fragile and incompletely mineralized bone) the morphology of the
specimen. A really bad polymer can torque, warp and split such a
specimen if it shrinks in aging; alter the specimen's appearance if
it yellows and darkens; alter so much as it ages that it is
difficult or impossible to remove without endangering the specimen;
and, especially if it is commercial preparation, introduce
contaminants that you are no aware of that can really damage the
specimen over time.

You can check a recent technical leaflet published by the Society
for the Preservation of Natural History Collections at
<URL:http://www.geo.ucalgary.ca/spnhc/>. Follow the links to SPNHC
publications and look for "Adhesives and Consolidants in Geological
and Paleontological Applications" (there are two parts to this: the
text and the wall chart). Hope this is of some help. Cheers,

Sally Shelton
President, SPNHC
Office of Collections Programs
National Museum of Natural History
Smithsonian Institution
Washington, DC   20560-0107
202-786-2601
Fax: 202-786-2328

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                  Conservation DistList Instance 12:48
                 Distributed: Monday, November 30, 1998
                       Message Id: cdl-12-48-001
                                  ***