I've noticed more people are showing more interest in reusing painted shells, I thought I'd give you a hand!I highly recommend doing this to all of your painted shells, why throw out and waste a perfectly good shell if you can save it?
It's really easy, and it's really exciting finding out what kind of shell is underneath!You can even do this with shells that have a clear sealant on them. However, if a shell looks like the paint goes all the way into the spiral, unless you can pull it out in one piece, toss the shell. Sometimes there is paint pooled in the spiral, still wet, and a crab will get stuck in it! I lost Fred this way, and I don't want anyone to put painted shells into their tank only to later find out there was still some in there. And unless you break the shell, you can't remove paint that's deep in the spiral. And if there's a stain left over that you can't remove, also be cautious, since shells are porous and I'm unsure of whether or not the chemicals in paint leeching into the crabs shell water can be dangerous or not.
You can use salt or fresh water to boil with, and if you can stand it, a bit of vinegar. You'll also need a hand towl (preferrably an old one that you won't miss) some newspapers to keep the mess level down, and an exacto knife, or butter knife, or sometimes even your fingernails.
Place your newspapers on a table so you don't get the paint chips all over, and boil your shell for awhile (this softens and loosens the paint)
Take the shell out and hold it in your hand with the towel so you don't burn or stab yourself and make an 'entry hole' with your knife to start scraping outwards from the entry hole (don't worry about damaging the shell. If it cracks as soon as you apply pressure to it, you don't want your crabs to use it anyways) scrape slowly and try to peel the paint, this will usually take off large chunks of paint at once.
If you take a break, or go to bed without finishing, just drop your shell into a cup of water to soak while you're away, this will keep the paint looser off the shell. You dont have to re boil it every time you start scraping, but it sure helps! yYou should push the shell against the table (or any hard surface) while you scrape to stabilize your hand. And always move the knife away from your hands as you scrape, never towards them.
Do NOT soak your shell in nail polish remover, paint thinner, etc. Shells are porous like our skin and absorb the chemicals. If you wish to soak your shell, soak it in water, dechlor or salt will both work. And don't soak it in just vinegar! Too much vinegar will dissolve the shell. Use vinegar sparingly, since the acidity can eat away at your shell 
you never know what cool shell is underneath the paint!
Just a side note, this is if you already have shells with paint on them. I'm not encouraging buying crabs in painted shells or the shells themselves! It just feeds the trade, and the less we buy, the less they get
Plus painted shells are ridiculously more expensive than natural ones. And it's hard, if not impossible sometimes, to tell what kind of shell you're buying
Let us know what goodies you find under there! Your welcome 
