Fordite

Fordite is the informal, non-brand name for cabochons made from the multi-layered linings of the assembly-line ovens where paint was sprayed on to cars, then baked in. After hundreds of successive firings, the hardened paint lining the oven was broken off into chunks and discarded, until some creative and enterprising amateur lapidarists tried cutting the chunks down into cabochons. Hundreds of high-temperature bakings have made this lightweight, fun material surprisingly durable, although its use in heavy-wear jewelry is not advised.