Cleaning without ruining natural shine

[sarabell]

I have only been collecting shells for 4 months.  How can you not living on a sub-tropical island <img src="smile/hapface01.gif" alt="smile/hapface01.gif" style="border:0" /> Anyway, I have found several small, 1 inch, snail shells that are very shiney and purple on the inside.  Before I found this site, I would soak in fresh water, along with my cowries, and ruined the natural shine.  I have since used the freeze/thaw method then the alcohol and have not had a problem.  My question now is, how do I clean the outside of these shells? If I soak it in anything, I will ruin the inside which is where the beauty is.  The outside of these shells have a thick, white hard substance on them.  I also have two shells that are very shiney and smooth on the inside, and have the leathery outside that I would like to get off.  I'm afraid if I soak them in bleach, I will ruin the naturally smooth, shiney inside.  I hope there is someone out there with the cleaning wisdom I'm looking for!!