Wikipedia
Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between . The powder melts, flows, and then hardens to a smooth, durable vitreous coating on metal, or on glass or ceramics.
The term "enamel" is most often restricted to work on metal, which is the subject of this article. Enameled glass is also called "painted". Fired enamelware is an integrated layered composite of glass and metal.
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.
Enameling is an old and widely adopted technology, for most of its history mainly used in jewelry and decorative art.
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. ("Enamelled" and "enamelling" are the preferred spellings in British English, while "enameled" and "enameling" are preferred in American English.)
Usage examples of "vitreous enamel".
Slight discolouration of vitreous enamel consistent with submersion in fairly highly concentrated sulphuric acid.
The brick hearth was filled by a four-door Aga: its racing-green vitreous enamel had darkened down the decades, and there were plenty of little chips in it.