Thanks Paul; in fact I did (pat on the head) search the archives before
posting and in frustration decided to just ask again.  :)   You are right,
they're not easy to sort through at all.

If the signs are a fine white powder on the shell's surface, can it not be
"wiped away" or is in more of an "eating away" or permanent
etching?   Luckily I have not encountered this yet and hope to keep it that
way.  :)

Nancy