I've tried to study this a bit, including polishing some shells myself to
see how they react in attempts to better detect tampering in shells I
buy.  I suspect the best way to easily discover enhanced shells is with a
stereoscopic microscope.  However not everyone is willing to go that far.
An easy way to detect enhancing is to turn the lights out at night and
shine a flashlight on the suspected shell sitting next to a known all
natural shell for comparison.  This highlights imperfections not normally
noticed during the day.  You can see micro scratches from polishing, brush
strokes from painting, and a lot more natural flaws as well.

Detecting painted shell get's tougher the better quality the paint job.  I
look at as many specimens as I can to build up a repertoire of what
possible variations the pattern could be.  After you have a good
repertoire, you can spot poor fake patterns easier.  Take a look at this
shell from the top fake shell distributors on ebay.
http://cgi.msn.ebay.com/ws/eBayISAPI.dll?
ViewItem&category=4838&item=6502355306&rd=1

When spoting painted shells especially notice if the species has a pattern
that is both on the margin and the dorsum.  If not, watch for over-
painting onto the margins.  Also watch for three dimensional spotting.
Spots can be painted on different layers of clear coat, giving them a
three dimensional look that the natural pattern doesn't have.

Poorly painted shells have detectable problems.  The longer the shell has
been dead, the harder it is to make it look live collected.  In many
cypraea species the margins have been built up by the animal more than the
dorsum.  After death, the margins begin to separate from the dorsum.  The
area where the dorsum and the margins meet seem to be near impossible
to "polish together" once separation begins.  Look carefully at this
crucial area where the margins and dorsum meet for unnatural lines.
Higher quality fakes overcome this "nacre separation" problem by building
up margins out of synthetic material.   I guess the stuff is some type of
polymer.

A master's work is extremely tough to detect by the naked eye, but it will
feel different in the hand than a natural shell.  It will most likely will
weigh less than it should because the polymers are lighter than calcium
carbonate.  Some of these polymers will generate static electricity and
pick up particles if rubbed like the old comb trick.

----------------------------------------------------------------------
[log in to unmask] - a forum for informal discussions on molluscs
To leave this list, click on the following web link:
http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1
Type your email address and name in the appropriate box and
click leave the list.
----------------------------------------------------------------------