Japanese cloisonné manufacture
Enamelling is a meticulous and extremely time-consuming craft. Enamels are a form of glass coloured with metallic oxides and applied as a paste, usually to a metallic body (generally of copper, although other metals can be used). When the object is fired in a kiln to an appropriate temperature, the enamels melt and fuse to the body. The object is then cooled and its surface is polished to a high-gloss finish.
There are various enamelling techniques. The simplest is champlevé, where a pattern or design is carved out of a metallic body, the enamel paste is applied into the resulting hollow, and the piece is then fired and polished.
In cloisonné enamelling fine wires are used to delineate the areas (cloisons in French, hence cloisonné) into which the enamel paste is applied. The wires serve a dual function: they can be an integral part of the decoration at the same time as preventing the molten enamels from flowing into adjoining areas during firing.
A design is first drawn in ink onto the metal body and fine wires, generally of brass, gold or silver are bent or hammered into shape and carefully glued along the lines of the design. This process is followed by the gluing on of small pieces of solder or the covering of the whole body with a thin layer of flux.
During firing the enamel paste melts and contracts so additional applications and firings may be required for the enamels to reach the required depth within the cloisons.
After each firing, any surplus hardened enamel is removed and the marks left by this process are ground down before the next layer of enamel is applied. In order to counter the effects of heat stress, counter-enamel is generally applied to the inside of the object.
Finally, after all the cloisons have been filled to the required depth, the surface of the vessel is ground until the edges of the wires are visible and the whole piece is then polished.
The grinding and polishing process involves the use of many different grades of stone and can in some cases take several months or even longer to complete.