If you are intending to cast silicone appliances for your makeup.. . well, anything that has come into contact with the sulfur-infused clay will prevent silicone from curing. I’ve heard rumors that it’s not even a good idea to say the word sulfur around uncured silicone! I hope I haven’t upset the sulfur clay aficionados out there, but facts are facts, and sulfur and (uncured) silicone just do not play well together. So why do manufacturers put sulfur in clay at all if it is so bad for curing silicone? According to Chavant®, maker of Professional Plastiline, NSP, Le Beau Touche, and Da Vinci Italian Plastilina, sulfur is used in some of its clays because it is an inexpensive nontoxic filler that enhances the surface texture of the clay, giving it a unique, silky feel.