Enamel is a type of allochromatic glass that consists usually of quartz sand, iron oxide, potassium oxide (potash) and borax (flux). These components form a transparent and colorless fondant after firing at temperatures between 700 and 900 degrees Celsius. Their plethora of colors are established by the addition of different metal oxides and/or chlorides. After thoroughly crushing and washing these materials a hydrated mass is formed (a fondant) which is then applied on a suitable, and completely clean metal (typically gold, silver or copper alloys).
Enamel can be applied to metal surfaces with engraved lines, engraved cells and raised borders that is fused at high temperature ovens creating a vitreous (glassy) surface. The fine art of enameling has many schools including (but not limited to) champleve, taile d'epargne, guilloche, cloisonne, plique a jour and miniature painting (french enamel).