[NHCOLL-L:3716] Re: ID of Shell versus Ivory/tusk

[Barry_Baker at fws.gov]

Bob,
If you have a cross-section view available, microscopic examination is
typically sufficient to distinguish ivory from shell.  The primary
distinguishing character is the presence of the Schreger pattern on
proboscidean ivory and its absence on shell.  A basic introduction to the
subject can be found in the following publication:

Espinoza, Edgard O., and Mary-Jacque Mann. 2000. Identification Guide for
Ivory and Ivory Substitutes, 3rd edition.

This guide is summarized on our web site:

http://www.lab.fws.gov/Ivory/index.html

Also, keep your eye open for the following paper that is in press:

Locke, Michael (in press). Structure of Ivory.  Journal of Morphology, in
press.

You can view the abstract at:

http://www3.interscience.wiley.com/cgi-bin/abstract/117870713/ABSTRACT?CRETRY=1&SRETRY=0

If you have electronic access to the journal, you can read the article now.
It provides a very comprehensive review of ivory micro-structure for a
broad range of species.  Hope this helps.

Sincerely,
Barry W. Baker

Forensic Scientist - Morphology
Morphology Section
U.S. National Fish & Wildlife Forensics Laboratory
1490 East Main Street
Ashland, Oregon 97520-1310
USA

Phone: 541.482.4191
Fax: 541.482.4989
E-mail: barry_baker at fws.gov
Web: http://www.lab.fws.gov

Adjunct Professor of Anthropology
Department of Sociology and Anthropology
Southern Oregon University
Ashland, Oregon





                                                                           
             "Bob Glotzhober"                                              
             <bglotzhober at ohio                                             
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             01/18/2008 12:01          [NHCOLL-L:3714] ID of Shell versus  
             PM                        Ivory/tusk                          
                                                                           
                                                                           
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Our archaeologists have an Archaic age (circa 4,000 ybp) gorget that they
are curious about. The older records indicated it was shell, but they
thought it might be ivory. I looked at it, and it seems to fit. The gorget
came from Glacial Kame culture – and with the rich supply of mastodon and
mammoth fossils found in Ohio, it could just as easily been made from tusk
ivory as from shell (we have some large species of mussels in Ohio
currently, and they did have trade with Gulf Coast cultures and had marine
shell also available.

So the question is, how to separate shell from ivory.
My first thought was a test for calcium carbonate with weak HCl acid – the
destructive sampling approach was not warmly received, but we do
occasionally approve destructive sampling in the right circumstances.

My next thought was doing the old Archimedes trick to determine density of
the object and compare that to known shells and known ivory. Does anyone
have a source of existing, standardized density for shell and ivory?

Are there any microscopic analyses that can be done without making thin
slices? Any other tests that anyone might suggest?

We await your ideas, suggestions and tried and true methods.

Bob Glotzhober



============================================
Robert C. Glotzhober                bglotzhober at ohiohistory.org
Senior Curator, Natural History             Ph. 614/ 297-2633
Ohio Historical Society
1982 Velma Avenue
Columbus, Ohio  43211-2497