Glassy but noncrystalline coatings for attractivedurable service in chemical, atmospheric, or moderately high-temperature environments areprovided by enamel or porcelain coating. Dry enameling is used for castings, such asbathtubs. The casting is heated to a high temperature,and then dry enamel powder is sprinkledover the surface, where it fuses. Firing temperatures for conventionalenameling of iron or steel ranges up to 870°C.Low-temperature enamels have been developed,permitting the enameling of aluminumand magnesium. Coatings of 75 to 500 μm are used for kitchenware,bathroom fixtures, highway signs, andwater heaters. Vitreous coatings with crystallinerefractory additives can protect stainless steelequipment at temperatures up to 950°C.
