By Harold McGee
In utensils called enamel-ware, powdered glass is fused into a thin layer onto the surface of iron or steel utensils. This was first done to cast iron early in the 19th century, and today enameled metal is widely used in the dairy, chemical, and brewing industries, as well as on bathtubs. In kitchen utensils, the metal diffuses the direct heat evenly, the ceramic layer is thin enough that it can expand and contract uniformly, and it protects the food from direct contact with the metal. Enamelware is reasonably durable, though it still requires some care: the ceramic layer can be chipped or damaged by quenching a hot pan in cold water.