Vitreous Enamel is glass that shares the same co-efficient of expansion as the metal it is being fused to. This action happens at approximately 1750 degrees .... depending on the particular enamel and the metal it is being fused to. A number of factors affect the outcome including the cooling rate and the atmospheric conditions during the heating and cooling process. This process, our process, is "Old World" enamel. The "modern" process is nothing more than colored epoxies.