The basis of all enamels is the application of fusible silicate or glass, colored with metallic oxides, all upon a metal ground. The varieties of enamels have already been described at length in the chapter on European enamels, but it will be convenient to summarize the processes here as they apply to Oriental as well as to Occidental enamels. In cloisonné enamel-work a metal base--of gold, silver, copper, or some other metal--has its design traced upon it by means of thin metal wires or strips soldered to the base and forming a number of divisions. These, when filled with the colored silicate (subjected to amalgamation by heat, and afterward polished) produce a beautiful patterned surface, the design of which appears traced in metal filaments. The Byzantine and the Greek enamelers executed their cloisonné enamels in gold, as likewise did the Anglo-Saxons, the Russians, the Chinese, and the Japanese in their finest work. In the plique à jour enamels we find what is really a variety of cloisonné rather than a class, as the plique à jour is cloisonné unbacked by a metal ground but much like a leaded stained-glass window in miniature. That is, if one holds a piece of plique à jour work to the light he will find it allows the light to pass through, whence its name. Champlevé enamel resembles cloisonné, but its pattern, instead of being traced by cloisons soldered on a metal base, is scooped out by a sort of deep engraving upon the metal base, these depressions being filled up with enamel, which is fired and then polished. The Celts, the Persians, and the enamelers of India worked in this manner. Respoussé enamel is, one may say, a variety of champlevé, or at least so closely akin to it that it is seldom considered as composing a class by itself, though I think it should be. In such enamel-work the design is wrought upon the metal base, not with cloisons as in cloisonné, nor by scooping out by a graver, as in true champlevé. Instead, the design is worked upon the metal by hammering out--respoussé--the depressions to be filled with the enamel. This is then fired and polished, as all enamel of any class has to be. Some of the enamels of India are such fine examples of work of this sort that they have passed as true champlevé. Finally, we come to the _painted_ enamels, such as those of Limoges. In the earliest examples of the painted class one finds the design applied directly to the metal base, grain by grain and layer by layer, in such a manner that the various fusings and glazings produce the results one finds in the marvelous old Limoges enamels; while in later work the enamel is fused upon the metal base, the designs being painted (in some instances printed) on the enamel.