Hi Aaron,
In the lab we extract rose bengal from bacterial slides using
acidified 50% ethyl alcohol.  On a shell you can't use the acid of
course, but 50% ethyl alcohol is probably your best bet.  For some
reason, the 50% solution seems to work better than either stronger or
weaker solutions.  Pure ethyl alcohol won't extract the dye at all.
You could also add a bit of ammonium hydroxide (household ammonia) to
the alcohol solution.
Regards,
Paul M.