Linda, It probably is shelly material, like a parietal glaze, but that covers the entire shell, covering the periostracum. Best to leave it on... Allen Aigen [log in to unmask] --- lindawbush <[log in to unmask]> wrote: Hello, Everyone! I ran into an unusual situation with a shell I got at auction the other night. It is an Elephant Snout type volute, not positive of the species yet. But it had what looked like a periostracum on it, partially gone. When I put it in weak bleach, it started coming off; but I discovered that it seemed to be a very thin colored glaze that looks like mica when it flakes off. I think this is not a true periostracum, but don't know what to call this layer. Do other volutes in this genus, Cymbium,I think, also have this glaze? I know very little about this group of volutes. Thanks, Linda