Enamels are made by painting a substrate, typically metal, with frit, a type of powdered glass. Minerals called color oxides provide coloration. After firing at a temperature of 750–850 degrees Celsius (1380–1560 degrees Fahrenheit), the result is a fused lamination of glass and metal.

Enamels have traditionally been used for decoration of precious objects, but have also been used for other purposes. In the 18th century, enamel painting enjoyed a vogue in Europe, especially as a medium for portrait miniatures. In the late 20th century, the technique of porcelain enamel on metal has been used as a durable medium for outdoor murals.

Source: Wikipedia