A powdered glassy substance colored by metal oxides, which is melted onto a metallic surface aided by alkaline FLUX. (read: a flowing or flow)Enamel was in use by the second millennium BCE on gold and silver, and later also on copper.
Because it turns into a liquid, flowing compound during firing, before solidifying upon cooling, it needs to be retained in compartments, or CLOISONS, to prevent an indiscriminate mixing of colors.
The surface may require additional grinding and polishing after firing. Much of ancient Greek gold was enameled, but the evidence is often lost due to degradation of the compound while buried.
Enamel was widely used in the Renaissance for opulent ornaments, but also in traditional Berber, Chinese, and Indian jewelry.
Modern substances, called cold enamel are paint or resin based and are not true enamel. In a related technique in porcelain production, enamel is fired onto a glazed surface.
Here are some of the styles of enameling:
Basse-taille: A technique in which the bottom surfaces of metal CLOISONS are worked into a relief, either by CHASING or engraving, and can be viewed through the translucent enamel.
Champlevé: A style in which the jeweler carves or cuts into the metal to make the CLOISONS to reccive the melted enamel, leaving thin walls between the compart-ments of different-colored vitreous melt.
Cloisonné: An approach in which the surface to be enameled is sectioned into small compartments for different-colored enamel. The CLOISONS are frequently formed by thin, flat metal wire soldered onto the substrate, but can also be formed by round or twisted wires.
Counter enamel: Mostly monochromatic or clear enamel melted to the metallic reverse of an object to counter the surface tension of the obverse. Sometimes the underlying metal is textured to provide a pattern that is visible through the enamel.
En plein sur fond reserve: A form of surface decoration in which enamel is used to create a vitrcous background.
En résille sur verre: A technique where enamel is fused into sunken gold-lined cells or incisions in a medallion or bead of translucent glass, then ground and polished until smooth.
Plique-à-jour: (backless enamel) A technique that uses metal partitions to separate colored enamels. In contrast to cloisonné enameling, there is no metal backing, and light can pass through. The result is simil ar to that achieved in stained glass.
I happen to think enamel is underrated and I would love to see more of it.