The glass coating on your bathtub began on Bronze Age rings
Vitreous enamel is powdered glass melted onto metal in a kiln, usually at 750 to 850 degrees Celsius, until it flows into a smooth, hard coat. The craft that decorated Mycenaean rings in the 13th century BC now covers cast-iron bathtubs, steel sinks and the panels of dishwashers and refrigerators.
The earliest enamel was cloisonné: glass set into tiny cells walled with gold. Craftsmen in Mesopotamia and then Egypt had used such cells since the 3rd millennium BC to grip stones and gems, and enamel probably arose as a cheaper way to get a similar look. Jewellery from Tutankhamun's tomb, around 1325 BC, is often called enamelled, but many scholars doubt its glass paste was ever fully melted, which leaves a group of Mycenaean rings from Cyprus as the first undisputed examples.
Celtic metalworkers took it up too. The Battersea Shield carries red enamel in 26 places, probably imitating the coral set into the Witham Shield, and Pliny the Elder noted that the Celts enamelled metal while Romans hardly knew the method. Medieval Europe gave the art its greatest importance, from Byzantine cloisonné images to Limoges in France, famous for champlevé from the 12th century and later for painted enamel.
Cloisonné reached China from Byzantium or the Islamic world in the 13th–14th centuries; a book of 1388 calls it Muslim ware. The most prized Chinese pieces date from the early Ming reigns of the Xuande and Jingtai emperors. Japan made no three-dimensional enamel objects until the 1830s, then advanced quickly; the German scientist Gottfried Wagener, hired by the government, worked with Namikawa Yasuyuki on a transparent black enamel for backgrounds. In the Mughal Empire, court enamellers called mīnākār peaked under Shah Jahan in the mid-17th century.
Since the 18th century enamel has moved beyond jewellery into ordinary goods: some cooking pots, steel sinks, bathtubs, laundry machines, marker boards and signs. The word came through Old French esmail from Old High German smelzan, to smelt, while vitreous comes from Latin for glassy. Enamel paint and the coating on enamelled wire share the name but are quite different materials.
Source: Vitreous enamel
