Dear Ted,
         One thing you might consider, is to use Liquid "silicon" on your
shells in order to perserve their color.  It can be purchased in the liquid
state, but I do not have an address for this form at this time...I normally
will thin this liquid even thinner, by at least 4 or 5 to 1 acetone, then
brush it on the shell.  I have seen Golden Cowries treated this way when they
were first taken 20 years ago and they look as bright and dark orange as any
fresh-taken specimens I get!  If you know anything about "Golden", they tend
to fade quickly!  If you can't find any liquid silicon, you can make your
own...you can get silicon grease from most auto parts stores, then  you can
use acetone or some other thinner to turn it into a liquid state.  give it a
try
          Sincerely,
           Ed [Schelling]