Another two cents...
 
I just finished cleaning a 9 and a half inch WHITE Haliotis rufescens.
Someone, somewhere had dripped black poly resin on the outside that
was tough as steel and it looked like a lost cause. So, I figured...what
the heck and decided I couldn't hurt it more than it was already no
matter what I used. Three applications of heavy duty paint stripper and
it looks as good as new with no ill effects on the shell!  This time,
taking a chance paid off.
 
K. Hutsell
 
 
Paul R. Monfils wrote:
>
> Actually, any kind of paint thinner should do a good job.  Mineral spirits is
> a good bet.  Don't use paint strippers though.  They are unnecessarily harsh,
> and some may contain acids.
> Paul M.