SWORD-FURNITURE
composed of this alloy, but those I have had the opportunity of examining were all of ordinary copper-tin-lead bronze. In the seventeenth century it was extensively employed, but the finest examples of it as a decorative alloy are found in the guards and other furniture of the swords of the last century and the first half of the present. The addition of gold to bronze in order to obtain a black patina has been long known to the Chinese. It is hence possible that the Japanese may have learned from them this peculiar property of gold; but the pure alloy of copper and gold, of the true shakudo, is essentially Japanese, and is unapproached in the beauty and richness of its patina by any alloy of the Chinese, either of old or recent times. Its rich deep tones of black, and the splendid polish which it is capable of receiving, render it alike a perfect ground for inlaid designs of gold, silver, and copper, and for being similarly inlaid in them. This alloy, too, possesses physical properties which are of extreme importance to the worker in metals, and enable him to manipulate and fashion it as he desires. It can be cast into any form; can be hammered into sheets and drawn into wire. No large castings, however, have been made of it. The method by which the black patina is produced is as follows: The object is first boiled in a lye prepared by lixiviating wood ashes; after which it is carefully polished, if necessary, with charcoal powder. It is then immersed in plum-vinegar containing common salt in solution, and, after being washed with a weak lye, is placed in a tub of water to remove all traces of alkali. After this treatment it is digested in a boiling solution of copper sulphate, verdigris, and water, to which sometimes potassium nitrate is added, and the desired patina is produced.
It is roughly stated above that shakudo is composed of 97 per cent of copper to 3 of gold. But, in truth, no less than fifteen grades of the alloy are used by Japanese craftsmen. The lowest of them—called chiusho—contains only traces of gold, and the highest has as much as 7 per cent of the precious metal. Analyses of seven specimens of shakudo made by Mr.
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