Thanks for all the advice re acid.  I was inclined to try it on some
Pectens, as advised by the writer of a shell encyclopedia I have.  (I'd
give the author, but naturally cannot remebre the name.)    Now, though,
I'm suitably terrified.
 
Re bleach:  I did find that bleach faded (mildly) the Junonia I found, and
the insides of some jewel boxes (I do not know the latin name).
 
HP