glaze has alot of minerals and metals in it, thats how they make different colors. there might be some that are non toxic and even a different makeup now. and yes ceramic bongs that are sold are not glazed inside but they do soak up some water and get a funky resin smell after using. i had an art teacher who was really cool, i once made a bead(smokestone) that she certainly asked me about.(too easy for a real art project) but it blew up in the kiln so i never got to use it. i dont really know if it is bad to use glaze inside (or cheaper) but the produced ones dont have it inside.