Thanks, Paul. Yours is a pretty good explanation. I'll try wetting my M. balthica shells and see if they turn "brighter."
Roland

>>> [log in to unmask] 06/01/02 02:29PM >>>
I doubt that the actual pigments have faded in such a short time. Beach
collected shells, even those in the best apparent condition, are usually
microscopically abraded by being repeatedly rolled around in the sand before
finally being deposited on the beach. While the shell is wet, the water
fills in the scratches and microscopic pits, and the shell appears shiny and
colorful, but when the shell dries it appears dull, and the colors are less
apparent. It's the same as wetting a piece of frosted glass. The glass
appears clear until it dries, then it again appears frosted. Have you tried
wetting the shells, to see if the color reappears?  If so, you can bring out
the color more permanently by applying mineral oil to the interiors, and
wiping off the excess.

Paul M.