Enamel (Fr. email; originally esmail, from the same root as smelt), the name given to vitrified substances applied chiefly to the surface of metals. Enamelling is practised (1) for purposes of utility, as in making the dial-plates of watches and clocks, coating the insides of culinary vessels, &c.; and (2) for producing artistic designs, portraits, and for ornamental purposes generally. The basis of all enamels is an easily fusible colourless glass, to which the desired colour and opacity are imparted by mixtures of metallic oxides. The mass, after being fused together and cooled, is reduced to a fine powder and washed, and the raw material thus obtained is variously applied to the surfaces to be covered according to the class of enamel being made. The whole is then exposed in a furnace (fired, as it is called) till the enamel is melted, when it adheres firmly to the metal. The metal most commonly used as a ground for enamel is copper; but for the finest kinds of enamel-work gold and silver are also used.
Artistic or Ornamental Enamelling.—This art is of great antiquity; it was to a limited extent practised by the Greeks; but enamels were more largely employed by the Romans, under whose dominion the art passed into Gaul and Britain. Enamelling has also been practised from a remote period in the East, Persia, India, China, and Japan, under a separate and distinct development; but there is nothing from which it can be inferred that the various methods were in use earlier than in Europe. As a decoration enamelling was more popular and attained to greater perfection in the middle ages than in classic times. It was extensively practised at Byzantium from the 4th until the 11th century, and afterwards in Italy, in the Rhenish provinces, and at Limoges in the south of France. The Byzantine and other early styles of enamel-work, down to the 14th century, were generally employed in ornamenting objects connected with the service of the church. Enamel was also greatly used in ornamenting jewelry, and vessels made for use or display in the mansions of the rich, such as salt-cellars, coffers, ewers, candlesticks, &c.; but these objects were principally made in the painted enamels introduced in France towards the end of the 15th century.
Distinguished with reference to the manner of execution, enamel-work may be divided into four kinds: (1) Cloisonnée, or inclosed, the method of the Byzantine school, in which the design is formed in a kind of metal case, generally gold or copper, and the several colours are separated by very delicate filigree gold bands, to prevent them running into one another. Of this style the grandest example extant is the famous Pala d'oro in St Mark's Church, Venice, some portions of which are Byzantine of the 10th century. (2) Champ-lévé, practised by the Rhenish and early Limoges schools. In this process the ornamental design, or the figures which were to be filled in with colour, were cut in the metal (generally copper) to some depth; and wherever two colours met, a thin partition of the metal was left to prevent the colours running into each other by fusion when fired. (3) Translucent enamel, which had its origin and was brought to great perfection in Italy, was composed of transparent enamel of every variety of colour, laid in thin coatings over the design, which was incised on the metal, generally silver, the figure or figures being slightly raised in low relief, and marked with the graver, so as to allow the drawing of the contours to be seen through the ground, instead of being formed by the coarse lines of the copper, as in the early Limoges enamels. (4) Surface-painted enamels, which may be divided into two stages. The first stage, which is known as the late Limoges style, sprang up about 1475, and flourished till 1630. In this the practice was to cover the metal plate with a coating of dark enamel for shadows, and to paint on this with white, sometimes having the hands and other parts of the figures completely coloured. The designs of the middle and best period were generally taken from well-known paintings or engravings of the period, and were strongly influenced by the Italian art of the time. This style soon degenerated, and gave place to the latest or miniature style, which was invented before the middle of the 16th century by Jean Toutin, a goldsmith at Château-dun, and carried to the highest perfection by Jean Petitot, a miniature-painter, who was born at Geneva, 1607, and resided long in England, and then in Paris. On his method the plate is covered with a white opaque enamel, and the colours are laid on this with a hair-pencil, and fixed by firing. The paints are prepared by grinding up coloured enamels with oil of spike, and when fused by the heat, they become incorporated with the enamel of the ground. The earlier enamellers of this school occupied themselves with miniatures, snuff-boxes, watch-cases, and other trinkets, till the period of the Revolution, when the art fell into disuse in France. In England, however, it was carried on with much success; and copies of portraits and pictures on a much larger scale than the French miniatures were executed by Henry Bone (1755-1834), and the German, Karl Muss (died 1824). Works of this description possess the obvious advantage of durability; but those various qualities of texture, and the delicacy of colour for which good works in oil or water-colour are prized, cannot be attained in enamel copies. The greater part of the artistic enamel-work of the present day is of Japanese fabrication, and consists of elvisonné work on a copper basin. Both in Paris and in Birmingham enamel-work of this class has been attempted with success; but designs can be executed in Japan at prices which defy the competition of western traders. In China both cloisonné and painted enamels are made in characteristic Chinese designs. At Jeypore in India a limited quantity of enamel- work on gold is executed in translucent colours which possess incomparable brilliancy. Enamel incrustations of various kinds are very largely used in the jewelry, goldsmith, and silversmith trades of Europe. See Garnier, Histoire de la Verrerie et de l'Émaillerie (1886); Bowes, Japanese Enamels (1885); and for enamelled earthenware, see the article POTTERY.
Enamelled Iron.—Since the beginning of the 19th century many attempts have been made to cover iron with a vitreous surface, and several patents have been taken for such methods of enamelling. The chief difficulty in applying enamels to iron arises from the tendency of the metal to oxidise before it reaches the temperature at which the enamel fuses, and to become brittle from the oxide combining with the silica of the enamel. This action being superficial, the mischief is the greater in proportion to the thinness of the iron. Therefore it is much easier to enamel thick cast-iron vessels than thin vessels made of sheet-iron. A glass may be made by combining either silicic acid or boracic acid with a base; the latter fuses at a lower temperature than the former, but the glass is much dearer and not so durable as the silica glass. The enamels used for coating iron consist of a mixture of silica and borax, with various basic substances, such as soda, oxide of tin, alumina, oxide of lead, &c. Lead is not, or ought not to be, used in the enamel for coating culinary vessels.
A great variety of articles, many of them beautifully decorated in colours, such as grate-fronts, clock-dials, panels of different kinds, sign-boards, tablets, and name-plates, are now executed in enamelled iron at a moderate cost. It is also applied to corrugated roofing. The effect of heat on enamelled iron especially is to expand the metal more than the enamel, and cause the latter to peel off. Acids find their way through minute invisible pores, which exist in the best enamel; and when once they reach the iron, they rapidly spread between it and the enamel, and undermine and strip it off. This kind of action is curiously shown by filling an enamelled vessel with a solution of sulphate of copper. The acid attacks the iron wherever pores exist, and little beads of metallic copper are deposited at all such spots; these beads go on growing until they are large enough to be very plainly seen. This is the severest test for trying the continuity of enamelled surfaces to which they can be subjected, as sulphate of copper will penetrate the glaze and body of ordinary earthenware.
The enamel of teeth is the very hard translucent white layer covering the working surfaces of the Dentine (q.v.) or ivory of the teeth of most mammals. See TEETH.