Any clay not made of precious metals. 

BRONZClay and COPPRclay and NEW White Copper clay can be pinched, rolled, sculptured, cut or manipulated any way you like. Then fire it and the binder burns away leaving a solid, pure bronze or copper object. Create jewelry, jewelry components, or custom-crafted specialized tools.

All Copper-Based clays need to be fired in a box of some kind filled with activated charcoal. Carefully read the instructions included with the packaging.

Made in the USA!