A square slump mold that guarantees a bottom as flat as your kiln shelf ? Unheard of? until this Big Glass Molds tool became available. No more wobbly square bowl for your pieces with this bottomless mold.You will get an bisque fired ceramic mold with slightly curved sides that allows you to take your fused glass to a new level.Form your glass piece up to 12 inches long x 12 inches wide (of any thickness you can create). The depth of this mold is 2 inches.