Metal, leather, ceramic, turtleshell, ivory, horn and cloth have all been used as supports for lacquer objects but the most common substrate is wood. For flat objects, hinoki (Japanese cypress) or Japanese cedar are typically used. For turned objects a variety of timbers (typically a ring-porous hardwood) is used. Timber is meticulously selected to be free of knots and other defects, with straight grain and even texture, and is then carefully prepared. Wood may be boiled to remove resins, or smoke seasoned and is often left for 10 years or more after seasoning before use. The final lacquer coating will add something like 0.75 mm all round (i.e. if piece of wood is 2 mm thick it will end up 3.5 mm thick) and this has to be allowed for in construction. A mixture of glue and lacquer is used as an adhesive for jointed pieces.
The first step in the process of creating a lacquer finish on the substrate is priming. This involves sealing the substrate against the ingress and egress of moisture and providing a foundation which effectively isolates the topmost coats from the substrate. It builds the foundation for the topcoats in the same way that gesso does for gold leaf. The first coat of the priming is raw lacquer and this penetrates and to some extent seals the wood surface and provides a good key for adhesion of subsequent coats. After this any defective parts of the wood are cut away and these and other irregularities are filled with a mixture of urushi, rice paste and wood dust (kokuso). This stopping is cut back when dry and cloth or paper is then applied over the entire surface with glue and lacquer. A number of layers of a mixture of lacquer, clay, and water (sabi) are then applied. Each one is left to dry and is rubbed down before the next is applied.
Wajima and Yamashina are the two main areas in Japan where clays suitable for urushi foundation are found. It is formed into small cakes with water then baked and ground up into a powder. The powder is sieved to give different grades. Coarser grades are used nearest the substrate and progressively finer material is used as the foundation is built up. The process of application drying and polishing continues using different grades of lacquer and abrasive until the final surface is achieved. The complete process and some of its many variations are described in detail by Quin (1882). Useful information is also given by Herberts (1963), Brommelle and Smith (1988) and in the various publications of the Tokyo National Research Institute of Cultural Properties.
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