Enamelling is the art of applying a vitreous material to an object, as decoration, to the surface of which it is made to adhere by heat. Metals are the usual foundations to which enamels are applied, but stone, earthenware, and glass may be enamelled. When one speaks of "an enamel" we understand it to mean a metal that is ornamented by a vitreous decoration fused and fixed to the metal surface by heat. There are three principal kinds of enamels: the "embedded or encrusted," the "translucent upon relief," and the "painted." Some enamelled objects have a mixture of two methods.

The embedded or so-called encrusted kind has two varieties, which are best known under their French names, the Cloisonn*š and the Champlev*š. When floated in a transparent state over a bas-relief, showing the chased details below, it is translucent, or, as it is called by the French, *šnaux de basse-taille. The painted is a later variety developed by the school of Limoges.

The Cloisonn*š is the oldest variety; it is that in which the Greek or Byzantine enamels are made, and also the Chinese. In this method of enamelling the plate or metal foundation which is to receive the enamel is first cut to the required shape, and a little rim of gold ribbon soldered around it.

The design is formed by narrow strips of gold ribbon or filigree, fastened to the foundation by a strong gum or cement, and bent to form the lines of the design. The cells thus formed are filled in with the enamel in a fine powdered state, or in a paste, the vitreous materials of the selected enamel having previously been tried, as to their colour and time required for perfect and equal fusion.

The piece is then placed in a furnace or "muffle," sufficiently open so that the progress of the fusing can be watched while firing, and withdrawn when perfectly fused. As the enamel generally sinks lower than the walls of the cells after fusion, it is necessary to add a second thin coating, or sometimes more, and to re-fire it in order to fill all the cavities. After this the work will require grinding down and polishing to level the surface and restore the brilliancy of the colours that may be slightly deadened by the cooling of the enamel.

The materials of enamel colours are metallic oxides. These colours are finely pulverized, washed, and mixed with vitreous compounds, called fluxes, which are easily fusible, and in melting impart an extra brilliancy to the colours, and form with them by fusion the almost imperishable substance of enamel.

The Champlev Enamels

The Champlev Enamels are made in the same way as the Cloisonn*š, with this exception, that instead of the thin gold ribbons or filigree work forming the design, the walls of the cells that compose the design and separate the enamel colours in the Champlev*š variety are formed by the hollowing out of the thick metal - usually copper and leaving the design to be formed out of the thin partitions that are left standing. The cavities are filled with the enamel mixtures and fused as in the Cloisonn*š method.

On account of the articles being small, and also being mostly made on a gold foundation, they were more likely to have been stolen or melted down, and this accounts in a great measure for the scarcity of Cloisonn*š enamels in our collections. The Champlev*š, on the other hand, being generally enamels on copper or brass, that from the cheapness of those materials, larger vessels and other objects were extensively made, and from both size and lesser value of the materials they were more likely to have escaped the melting-pot.

When the foundation of the Champlev*š enamels was copper, the lines of this metal that formed the design would be gilt with an amalgam of melted gold and mercury, and the piece re-fired at a lower temperature, in order not to injure or disturb the enamel surface.

"Translucent" Enamel

"Translucent" Enamel upon reliefs known as de basse taille is the art of enamelling reliefs of silver or gold that have previously been chased or engraved with the design required. The enamel is laid on in various degrees of thickness, according to the strength of shading or depth of tone required. The transparent varieties of enamels are selected for these works, and opaque varieties avoided.

"Painted" Enamels

"Painted" Enamels were suggested by the translucent enamels upon reliefs. The extensive demand for the latter variety, and the great number executed, gave rise to the invention of using enamel colours as in oil-painting; that is, instead of engraving the subject or design previously on the metal, the method of expressing with the brush the drawing and the light and shade with the enamel colours direct was resorted to, on grounds specially prepared upon copper surfaces. Labarte believes that the modification in the art of glass painting introduced in the fourteenth century had the effect of causing enamel painters to experiment in painting with the enamel colours direct, as in painting on glass.

About this time the method of painting on glass was introduced, which formerly was decorated by simply using the pieces of stained or coloured glass as in mosaic work, the only difference between the superficial glass painting and the painting in enamels being that in the latter the opaque enamel colours are used instead of the transparent as in glass painting. It was, however, a considerable time from the introduction of painting on enamels before any good specimens of the art were executed.

Among the earliest specimens of Cloisonn*š enamels was the golden altar given to the cathedral of Sta. Sophia at Constantinople by Justinian.