Mark,
  There was a technique described for bringing out patterns in pliocene
fossils.  I believe that one soaks the shell in bleach for a period of
time and then exposes it to UV radiation.  If you are interested in trying
it, I can did up the reference for you.  I believe it was in an issue of
the journal CURATOR.
 
Charlie
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Charlie Sturm, Jr
Research Associate - Section of Invertebrate Zoology
                     Carnegie Museum of Natural History, Pittsburgh, PA
Assistant Professor - Family Medicine
 
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