Hi Eliza -- I use Mexican pottery clay and also a white self-hardening clay
that I order from Sax or Nasco -- takes a few days to dry thoroughly. It's
tough without a kiln but I tell the kids not to make anything too skinny or
long -- and tell them how to recycle it at home (add water) should it break
-- wish I did have a kiln, though!
Liz in rural NY