Enamel is, in the strict sense, the vitreous glaze or glazes fused on the surface of metallic objects and is a general term applied to objects decorated in this way. Enamel, a soft glass, is a compound of sand or flint, soda potash and red lead, which when melted produce a colorless, clear material called flux. While in a state of fusion, oxides of metal are added to color it, which stain the flux throughout its mass. The enamel, after being stirred, is poured on to a slab in cakes of about 12 cm in diameter. Enamel is made in varying degrees of hardness, and the harder the enamel the greater the heat required to fuse it and the greater the durability. The cakes of enamel are broken up and ground to powder in a mortar, washed and spread on the metal. The object is then placed in a furnace while the powdered enamel fuses with its metal base.
It is not known when enamels were first made, for as yet none has been found belonging to the time of the Assyrians or Phoenicians. The earliest examples are six gold rings, found in a Mycenaean tomb of the 13th century BC at Kouklia, Cyprus, which have true cloisonne enameling, i.e. enamel fused in cells formed by thin metal strips bent to the outline of the pattern and soldered to the metal base. Outside Mycenaean and Greek art, the most ancient examples are bronze ornaments of the 9th century BC from a cemetery at Koban in the Caucasus. From the 3rd century BC Celtic craftsmen substituted red enamel for coral, as on the Witham Shield (now in the British Museum), on which is used the technique of champleve enameling, i.e. enamel fused in troughs or cells cut out in the metal baseplate. Enamels were made in the northern provinces of the Roman empire and reappear in the 6th century AD in Anglo-Saxon England, e.g. the Sutton Hoo Burial (now in the British Museum).
The great revival of cloisonne enamel commenced in Constantinople in the 10th century AD. The masterpiece of this Byzantine enamel is the Pala d'Oro in St Mark's, Venice. In the 12th century a new style in the champleve technique was begun in the valleys of the Rhine and Meuse, at Limoges in France and also in northern Spain. The undoubted masterpiece of this period is the pulpit at Klosterneuberg, near Vienna, by Nicholas of Verdun (1181-1205).
In the late 13th century a new method of enameling was discovered in Italy, known as 'basse-taille', i.e. a colored translucent enamel fused over a design engraved in low relief below the level of the surrounding metal so that after firing the enamel is flush with the surrounding metal area. An outstanding example of this technique is the Royal Gold Cup of the kings of France and England (in the British Museum) made in Paris about 1380. A late medieval development was the plique-a-jour enamel, in which the translucent enamel is fused in an openwork cloisonne frame, like a stained-glass window. At the same time, enameling the surface of objects in the round was introduced, particularly for jewelery.
In the 15th century, in northern Italy and at Limoges, 'painted enamels' were first made, i.e. colored enamel applied by brush, spatula or point over a design scratched in outline on the metal baseplate. The most famous craftsmen of this method were Nardon Penicaud (1474-1539), Pierre Raymond, Leonard Limousin and Jean Penicaud.
By the 17th century this style of enamel had declined and was eclipsed by the miniature painted enamels, especially those of the Toutin family in Paris and the Huaud family in Geneva. However, in these enamels and the Battersea transfer-printed enamels the colors are not enamels but are applied after the ground enamel is fired and fused, and are therefore not properly speaking within the category of enamels.'