I have found it takes several days soaking in the bleach to remove the
periostracum from salt water shells - a Pleuroplaca gigantea for instance.
You have to just be patient and leave it for several days.  Eventually it
comes off.

S. Edwards
Huntsville, AL

----- Original Message -----
From: "Paul Monfils" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 24, 2002 8:16 AM
Subject: Re: periostracum question


> Acid has little effect on periostracum, but has an extreme effect on
> carbonate salts, which is what the shell is made of. Muriatic acid won't
> remove the periostracum from the shell, but it will quickly remove the
shell
> from the periostracum. Vinegar and other weak acids will do the same
thing,
> just more slowly. Organic solvents like alcohols, acetone, hydrocarbons,
> etc. will have no effect either on shell or periostracum. You definitely
> need a fairly strong base to dissolve periostracum without dissolving
shell.
> I am very surprised that bleach didn't work. By "bleach" I mean a liquid
> bleach containing hypochlorite - like Chlorox. That should dissolve
> periostracum. If it doesn't, you can try oven cleaner or drain cleaner, or
a
> solution of sodium hydroxide or potassium hydroxide (I recommend these in
> view of your stated use for the shells. I wouldn't recommend these methods
> for specimen shells to be placed in a collection). Handle these chemicals
> with care. They also dissolve skin.
>
> Paul M.
>