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 vitreous coating. The word vitreous comes from the Latin vitreus, meaning "glassy".

Enamel can be used on metal, glass, ceramics, stone, or any material that will withstand the fusing temperature. In technical terms fired enamelware is an integrated layered composite of glass and another material (or more glass). The term "enamel" is most often restricted to work on metal, which is the subject of this article. Essentially the same technique used with other bases is known by different terms: on glass as enamelled glass, or "painted glass", and on pottery it is called overglaze decoration, "overglaze enamels" or "enamelling". The craft is called "enamelling", the artists "enamellers" and the objects produced can be called "enamels".

Enamelling is an old and widely adopted technology, for most of its history mainly used in jewellery and decorative art. Since the 18th century, enamels have also been applied to many metal consumer objects, such as some cooking vessels, steel sinks, and cast-iron bathtubs. It has also been used on some appliances, such as dishwashers, laundry machines, and refrigerators, and on marker boards and signage.

The term "enamel" has also sometimes been applied to industrial materials other than vitreous enamel, such as enamel paint and the polymers coating enameled wire; these actually are very different in materials science terms.

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. "Enamelled" and "enamelling" are the preferred spellings in British English, while "enameled" and "enameling" are preferred in American English.

The earliest enamel all used the cloisonné technique, placing the enamel within small cells with gold walls. This had been used as a technique to hold pieces of stone and gems tightly in place since the 3rd millennium BC, for example in Mesopotamia, and then Egypt. Enamel seems likely to have developed as a cheaper method of achieving similar results.

The earliest undisputed objects known to use enamel are a group of Mycenaean rings from Cyprus, dated to the 13th century BC. Although Egyptian pieces, including jewellery from the Tomb of Tutankhamun of c. 1325 BC, are frequently described as using "enamel", many scholars doubt the glass paste was sufficiently melted to be properly so described, and use terms such as "glass-paste". It seems possible that in Egyptian conditions the melting point of the glass and gold were too close to make enamel a viable technique. Nonetheless, there appear to be a few actual examples of enamel, perhaps from the Third Intermediate Period of Egypt (beginning 1070 BC) on. But it remained rare in both Egypt and Greece.

The technique appears in the Koban culture of the northern and central Caucasus, and was perhaps carried by the Sarmatians to the ancient Celts. Red enamel is used in 26 places on the Battersea Shield (c.350–50 BC), probably as an imitation of the red Mediterranean coral, which is used on the Witham Shield (400–300 BC). Pliny the Elder mentions the Celts' use of the technique on metal, which the Romans in his day hardly knew. The Staffordshire Moorlands Pan is a 2nd-century AD souvenir of Hadrian's Wall, made for the Roman military market, which has swirling enamel decoration in a Celtic style. In Britain, probably through preserved Celtic craft skills, enamel survived until the hanging bowls of early Anglo-Saxon art.