The "oh so close," thread has brought out a lot of information.
Here are my "dos centavos" worth;
 
Protecting your cowries from "The Evil Traid" -- as one might
call bright light, moisture and heat -- is the best route for cowries
that start out in excellent condition. Let's face it, it is only down-
hill from perfection!
 
The antithesis of "The Evil Triad" is.... the "Freezer." Fresh, dry
(empty!) cowries fade -- it can't really be avoided. But the initial
fading away of color is slowed considerably if the specimen is kept in
a freezer -- the colder the freezer, the slower the color loss.
 
Now, don't just toss those precious things into your icebox! Wrap each
one in a dry paper towel and alot the batch to -- what else? -- a zip
top freezer bag. The paper and the bag greatly reduce the chance of
thermal shock. This also means that you should give the specimens
a chance to slowly return to room temperature before viewing them.
 
Restoring the faded shells to their former glory is a daunting task. The
chief method that I am aware of is creditable (in my limited knowledge)
to C. M. Burgess. A couple of days before the cowry is to be displayed,
place it in a container of DISTILLED water. Place that in the
refrigerator -- NOT the freezer. An alternative is to wrap the cowry in
a paper towel which has been dipped in DISTILLED water.
 
My experience has been that the splendid finish of Cypraea degrades
rapidly once the animal that produced and maintained it is dead.
Organisms in the ocean begin to attach to the surface. Within a
couple of days, the first signs of these doers-of-damage become
evident -- and that's if the surf isn't up! A few hours of 'sand-
blasting' under the caresses of 8-foot high swells (i.e., 12-foot-plus
surf) leaves the finish ruined.
 
As I have discussed previously and mentioned above, "it's all down-
hill from here" for a cowry's shine. Dulled surfaces can be glossed
by oils and greases. The roughened surface can be smoothed by Jeweler's
Rouge, but the original finish never gets better and never is reattained
by human effort.
 
To end on a philosophical note, the shell was doomed to degrade anyhow,
so enjoy it while you have it!
 
Aloha,
 
makuabob (a.k.a.Bob Dayle)