You can pick up Silicon Carbide grit pretty cheap online ( impure moissanite ). I have several tumblers, but have yet to finish the process of making polished gems- but it is still on my bucket list :). I have made lots of "sea glass: though. I have taken quite a bit to the local beach ( about 40 miles north of Palm Beach Fl. ) I toss it into the surf, figuring it will make some beachcombers happy. My logic is that once it has been in the ocean a few days, it will actually be sea glass. I would not make that claim for any of the glass that comes straight out of the tumbler though. Next time you visit a craft show and see folks with "Sea glass" Jewelry, note if they have separate displays for "real" sea glass, and man made.