Page:Brinkley - Japan - Volume 7.djvu/401

 was carefully polished, first with charcoal and afterwards with emery powder, a brush of split bamboo (called sasara) being employed for the purpose. It was then immersed in plum-juice, afterwards covered with a mixture of mercury and gold-dust, and finally heated to volatilise the mercury. Polishing by friction with steel needles, and, if necessary, "colour-finishing" (iroage) were the final processes. These descriptions apply to silver plating also.  —This statement indicates that refining processes of great efficiency were adopted in Japan. That is the case; and considerable interest attaches to the fact, for these processes seem to have been devised, in great part, by the Japanese themselves. Mr. W. Gowland says: "When gold was found to contain an undue proportion of silver, it was submitted to a curious process for the separation of the latter metal. It was first reduced to a coarse powder by heating it to near its melting-point and then rubbing it on an iron plate with a stone or iron rubber. The coarsely powdered gold was then mixed with common salt, and a certain proportion of clay, and piled up in the form of a cone on an earthen dish. The whole was then placed in a furnace containing charcoal fuel, and was kept at a red heat for at least twelve hours, by which means the silver was converted into chloride. The dish with its contents was then removed, washed with hot brine and water, the silver chloride was dissolved, and the gold left in a purified state." The test for silver was made with the touchstone, but the test for copper was effected by a method "unique in assaying operations." The metal was heated to redness over a charcoal fire, and when at the proper temperature, was rubbed with a stick of hinoki (the wood of the Thaya obtusa) and then immersed in water. The presence of copper and its approximate amount were determined by the colour and appearance presented by the part to which the stick of wood had been applied. So successful were the old operators in the application of this test that it is rare to find more than 0.25 to 0.35 per cent of copper in the old gold coins. If the test showed an excess of copper, it was removed by cupellation with lead.  — In the case of gold this was effected by painting the object with a mixture of iron sulphate, copper sulphate, potassium nitrate, calcined sodium, chloride and resin, made into a paste with water. It was then carefully heated on a grating over a charcoal fire, subsequently immersed in a solution of common salt and then washed with water, the silver being dissolved out of the upper layer of the alloy and a surface of pure gold left (Gowland). In practice, the kinzokushi obtained his nitrate of potash by using gunpowder. In the case of silver, the following interesting account is given by Mr. 