Enamel is a kind of composite material which is coated with one or several layers of enamel on the surface of metal and firmly bonded through physical and chemical reactions after firing. It used to be called enamel. It not only has the inherent mechanical strength and processability of metal, but also has the corrosion resistance, wear resistance, heat resistance, non-toxicity and decoration of the coating. Enamel originated from glass decorative metal.