there used to be a sculpey glaze available from polyform plastics, the
makers of sculpey. i have some that i ordered a long time ago. it works
great! i'm pretty sure i've seen something like it at the art/crafts
stores... i just used it to give jewelry a shiny finish. i don't think you
need to coat sculpey with anything to make it waterproof since its a
plastic... check this out: http://www.sculpey.com/