Processes of Enamelling.
The basis of most of the enamels on copper is a fusible silicate, or colourless glass mixed with metallic oxides, reduced to a fine powder, which is applied according to the skill of the artist. The metal, with the enamel powder upon it, is then fired until it is melted and adheres to the metal. The different treatments help the expert to distinguish the period when a specimen under investigation was made, and to some extent the place of its manufacture. There is the translucent enamel, which shows up the design through the vitreous matter, a method originally adopted in Italy. Another process was that of applying different colours over an incised pattern, the figures or pictures being usually engraved in low relief. Coarser lines of engraving were used on the copper basis of the early enamels made at Limoges. Those of somewhat later date may be distinguished by the surface-painted enamels adopted in the later style, which flourished until about 1630. In this process dark enamel for the shadows was placed over the metal plate, the picture being painted in white with some portions in colour; a thin enamel surface was then given and the whole fired. The later surface-painted enamels were for the most part copies of well-known paintings or engravings, the colour or enamel being afterwards fixed by firing. In the process of enamelling known as champlevé the design was cut into the metal, the pattern or incisions made filled with colours, the enamels being then fused; the basis was nearly always of copper. The cloisonné enamel was generally on a brass basis, and as in the more recent examples from China and Japan, the cloisons or tiny cells of metal were filled with the right and appropriate colours; afterwards subjected to heat. In some cases the metal foundation is in the centre and cloisons or cells formed on either side of it. There is something about the old enamels of this type besides the wear and tear of centuries which distinguishes them from the more modern, which, generally speaking, are more brilliant in colouring, cruder and sharper in design, and without that beautiful tone which is so pleasing in the antique.