Vitreous enamel

Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C (1,380 and 1,560 °F). The powder melts, flows, and then hardens to a smooth, durable coating on metal, or on glass or ceramics. So in technical terms fired enamelware is an integrated layered composite of glass and metal. Enamelling is an old and widely adopted technology, for most of its history mainly used in jewelry and decorative art. "Enamelled" and "enamelling" are the preferred spellings in British English, while "enameled" and "enameling" are preferred in American English.

The term "enamel" is most often restricted to work on metal, which is the subject of this article. Enamelled glass is also called "painted", and overglaze decoration to pottery is often called enamelling. The word enamel comes from the Old High German word smelzan (to smelt) via the Old French esmail, or from a Latin word smaltum, first found in a 9th-century life of Leo IV. Used as a noun, "an enamel" is usually a small decorative object coated with enamel.

Since the 19th century the term applies also to industrial materials and many metal consumer objects, such as some cooking vessels, dishwashers, laundry machines, sinks, and tubs.

The ancient Egyptians applied enamels to stone objects, pottery, and sometimes jewellery, although to the last less often than in contemporaneous cultures in the Near East. The ancient Greeks, Celts, Georgians, and Chinese also used enamel on metal objects.

Enamel was also used to decorate glass vessels during the Roman period, and there is evidence of this as early as the late Republican and early Imperial periods in the Levant, Egypt, Britain and around the Black Sea. Enamel powder could be produced in two ways, either by powdering coloured glass, or by mixing colourless glass powder with pigments such as a metallic oxide.

...
Wikipedia