the calcified tissue that covers the crown of a tooth. Enamel is secreted by special epithelial cells called ameloblasts, which die after the tooth is formed and are converted into enamel prisms, radially arranged slender fibers (3–5 microns in diameter) adjoining one another. Enamel, one of the hardest tissues in the animal organism, contains about 97 percent mineral matter, mainly phosphate and carbonate compounds of calcium, as well as a small amount of silicates. It protects the tooth from wear. It does not regenerate after damage. Damage to the enamel is observed in cases of caries, fluorosis, and other instances.
a type of low-melting, primarily opaque, glass, given different colors by the addition of metallic oxides and fused in one or several thin layers to a metal (enameling). The term “enamel” is also often used for low-melting opaque white or colored glazes used to coat and decorate ceramic and glass articles.
The principal components of virtually all enamels are silicon dioxide, SiO2, boron anhydride, B2O3, aluminum oxide, A12O3, titanium dioxide, TiO2, certain fluorides, and the oxides of alkali and alkaline earth metals, lead, and zinc. It is customary to divide enamels into ground-coat enamels and cover-coat enamels. The ground-coat enamels, which include in their composition adhesive substances, primarily oxides of cobalt and nickel, are used to apply a layer that adheres well to metal and is intermediate between the cover (external) layer of the enamel and the metal. Cover-coat enamels, which adhere well to metal, are applied without a ground-coat.
To prepare enamel, a mixture of feldspar, sand, or quartz, along with fluorite, borax, boric acid, soda, saltpeter, cryolite, and other ingredients, is melted in a furnace at 1150°–1550°C and is then poured into water for granulation. The granules are crushed in ball mills in the presence of water, clay, and other materials to obtain a stable suspension of fine particles, called the enamel slip. The metal is first covered with a coat of slip and then dried and roasted (at 500°–1400°C, depending on the metal being coated), after which the outer enamel is applied in one or two layers, each layer being fired separately. The slip may be applied by immersion, pouring, or spraying, or it may be applied electrostatically. Articles are fired in periodic kilns or continuous furnaces.
Enamels protect metals from corrosion and make them more attractive in appearance. They are applied primarily to cast iron and steel; they are also often applied to articles made of copper, aluminum, silver, or various alloys. Enameled metals are primarily used in the food-processing, chemical, pharmaceutical, electrical engineering, and construction industries. Refractory and corrosion-resistant enamel coatings are used in jet engines and in apparatus used in a highly corrosive environment; they are also used in thermal processing and the hot deformation of special alloys.
S. S. SOLNTSEV
Enamel art. The decoration of gold, silver, and copper articles, such as vessels and jewelry, with enamel is one of the oldest techniques in the art of jewelry-making. Both cold (without firing) enameling and hot enameling are practiced; in the latter case, the pasty mass colored by metallic oxides is applied to a specially treated surface and then fired, which produces a vitreous colored layer. Different enamels are distinguished according to the method of application and type of adhesion to the surface of the material. In cloisonne enamel, the enamel is laid in partitioned off compartments formed by fine metal strips soldered on a metallic surface edgewise along the lines of a design, thus following the exact lines of the contour. In champlevé enamel, the enamel is laid in troughs made in the metal by carving, stamping, or casting; such enamels are distinguished by deep colors. Basse-taille enamel (stamped or cast) can be transparent or opaque. The basse-taille technique makes it possible to represent three-dimensional shapes and to achieve various artistic effects, since during fusion the molten enamel flows down from the higher parts of the relief, which gives rise to alternating transparent and opaque areas, thus creating variations of shade. In painted enamel, a metal article is first covered with enamel and is then decorated with enamel paint (refractory paints after the 17th century). Enamels are also applied on filigree and engravings and can be inlaid with gold and silver.
The oldest extant enamels are the gold ornaments and amulets of ancient Egypt, executed in a cloisonné-type technique. The best example of early European cloisonne enamel is the facing of the altar walls in the church of Sant’ Ambrogio in Milan, executed by the ninth-century master Wolvinius. Cloisonne enameling on gold flourished in Byzantium in the tenth to 12th centuries. By the 12th century, various European schools of enameling had emerged: the Mosan school, in the Maas (Meuse) River valley; the school in the Lorraine region (the masters Godefroid de Claire and Nicholas of Verdun), the Rhenish school, centered on Cologne (the monk-enamelists Eilbertus and Fredericius), and the Limoges school (seeLIMOGES ENAMEL). European enamels, used chiefly to decorate ecclesiastical objects, were closely linked with the interior ornamentation of cathedrals and stained glass-work. Secular enameled articles appeared at the turn of the 15th century. Opaque enamels were replaced by transparent enamels applied on engravings, with the use of gold lines and inlays. In the 18th century, miniature enamel portraits and other objects of pictorial art, stylistically resembling easel painting, became the leading form of enamelwork. The art of enameling, a laborious technique, declined in the 19th century, reemerging only during the modernist era in Paris, Brussels, and Vienna, when the production of objects of personal adornment, snuffboxes, and fans combined enamels with precious stones, pearls, and the like (C. Popelin, R. Lalique, and P. Grandhomme).
Enameling has been known in China since the seventh century and was developed extensively in the 14th to 17th centuries. It was used to decorate silent weapons, small chests, snuffboxes, and the like with symbolic plant motifs and images of birds and animals.
In what is now the USSR, enamels were made in the third to fifth centuries in the Dnieper Region, for example, bracelets and fibulae with red, light blue, green, and white enamel. Cloisonne enamels from 11th century Kievan Rus’ have been preserved. Byzantine influence is evident in Russian cloisonne enamels on silver and gold of the 12th and 13th centuries and in medieval Georgian enamels on gold. Georgian enamels were not as subtly executed as Byzantine enamels, and they differ from Russian enamels in their more brilliant colors (the Khakhuli hinged icon, 12th century, Art Museum of the Georgian SSR, Tbilisi). In the 16th and 17th centuries, enamel on filigree was common among the Moscow masters, who used transparent multicolored enamels of thick, rich tones to decorate gold articles (I. Popov and other masters of the Armory) with scenes and designs resembling the ornamentation of the illuminated manuscripts of the same period. The art of Russian painted enamel, called Usol’e enamelwork, flourished in Sol’vychegodsk in the 17th century. The development of painted enamel on copper reduced the cost of enameled articles and broadened the range of objects decorated with enamel to include, in addition to religious objects, small chests, goblets, rouge pots, flasks, spoons, and the like. Painted-enamel icons and other articles were made in Rostov Velikii in the 18th and 19th centuries. Miniature enamel portraits were executed in the 18th century by G. S. Musikiiskii, A. G. Ovsov, I. P. Refusitskii, and the painter A. P. Antropov. M. V. Lomonosov developed a new range of enamel colors from domestic materials. A class in enamelwork was established at the St. Petersburg Academy of Arts (first mentioned in 1781). At the turn of the 20th century, enameled articles were produced by the Fabergé, Khlebnikov, Ovchinnikov, and Grachev companies.
In the USSR, painted enamels and enamels on filigree, engravings, and stamped relief are produced. The Rostovskaia Finift’ Factory in Rostov-Iaroslavskii is the major center of enamelwork, continuing the tradition of painted enamel begun in the 18th century (brooches, powder boxes, and small chests). It produces enamels primarily with decorative colored designs, as well as enamels with genre miniatures. Leading enamel artists include A. M. Kokin, V. V. Gorskii, I. I. Soldatov, and V. G. Pitelin.