Enamels are vitreous coatings applied to the surface of pottery or metals, though the name is sometimes restricted to the latter case only. The vitreous coating is generally an easily fusible glass - often a lead glass - containing oxide of tin, or other substance, to render it opaque. In the case of enamelled culinary articles, lead glass is unsuitable, and should never be used, a potash or soda glass being best employed. Coloured glasses are obtained by the addition of different metallic oxides. When obtained the glasses are finely powdered, spread over the surface to be enamelled, and fused on. In the case of pottery the fusion takes place easily, but the enamelling of metals is not so readily accomplished. Enamels are chiefly employed for ornamental and artistic purposes, and also as a protection for metals, to prevent them oxidising, etc. Thus for the latter purpose they are largely used as a coating for the interior of saucepans and kitchen articles, baths, sheet iron for advertising purposes, etc. Enamelling for ornaments is an art of great antiquity, and examples have been found from the prehistoric ages, while it is known to have been practised by the Egyptians and Assyrians several centuries B.C. The analysis of coloured enamels of these times has also shown that they used the same substances for colouring the glasses as are now generally employed. Examples of Roman enamelled work are existent, but the art attained to its greatest popularity in the Middle Ages. Various modes of ornamentation were employed, as Champ Levi, much practised at Limoges, which from the 12th to the 14th centuries was the chief seat of the art. In this the pattern was engraved on a sheet of metal, the parts to be enamelled being hollowed out, and the hollows filled with the enamel, fused, and afterwards ground and polished. Cloisonne, the style of the Byzantine school, which flourished during the 10th century. The design is traced by thin bands of metals, frequently gold, fixed to the metallic base, the space between the bands being filled with the enamel. This method is also much employed at the present time in Chinese and Japanese ornamentation. During the 13th century translucent enamels were largely used, chiefly in Italy. The design was engraved on the metal, usually silver or gold, and the enamel applied so that its varying thickness produced the shades necessary. Afterwards enamels were largely employed for the purpose of surface painting. In the earliest style, Limoges, 16th century, the metal was covered with a dark enamel, upon which the painting was done in light colours. In the latter style, which flourished much in England and Paris, a white opaque enamel was laid upon the plate, and the painting was executed in coloured enamels mixed in a suitable medium, each colour being separately fused. This was very popular during the last century for miniature trinkets, watch-cases, snuff-boxes, and other small articles, though in England larger works were often done in enamel.