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Many fine crystal balls are made in Japan, the materials being found in large, clear masses in the mountains on the islands of Nippon and Fusiyama and also in the granitic rocks of Central Japan. It is stated, however, that much of the Japanese material really comes from China. The Japanese methods of working rock-crystals are extremely simple and depend more upon the skill and patience of the workers than upon the tools at their command. Our illustration, taken from a sketch made by an Oriental traveller, shows the process of manufacturing crystal balls. The rough mass of crystal is gradually rounded by careful chipping with a small steel hammer. With the aid of this tool alone a perfect sphere is formed. The Japanese workmen thoroughly understand the fracture of the mineral, and know just when to apply chipping and when hammering. The crystal, having been reduced to a spherical form, is handed to a grinder, whose tools consist of cylindrical pieces of cast iron, about a foot in length, and full of perforations. These cylinders are of different curvatures, according to the size of the crystal to be ground. Powdered emery and garnet are used for the first polishing. Plenty of water is supplied during the process, and the balls are kept constantly turning, in order to secure a true spherical surface. Sometimes they are fixed on the end of a hollow tube and kept dexterously turning in the hand until smooth. The final polishing is effected with crocus or rouge (finely divided hematite), giving a splendid lustrous surface. As hand labor is exclusively used, the manufacture of crystal objects according to the Japanese methods is extremely laborious and slow. (Kunz, "The Occurrence and Manipulation of Rock Crystal," Scientific American, vol. lv, pp. 103, 104 (Aug. 14, 1886). Trans. N. Y. Acad. Sciences, May 30, 1886.)
In Germany and France and in the United States, the fabrication of rock-crystal is accomplished almost entirely by machinery. The crystal to be shaped into a ball is placed against a semicircular groove worn in huge grindstones. The accompanying illustration shows the method practised in Oberstein, Germany. The workman has his feet firmly braced against a support, and, resting upon his chest, presses the crystal against the revolving grindstone. It is unnecessary to add that the practice is extremely unwholesome and develops early consumption among the workers. A constant stream of water is kept flowing over the stone so that the crystal shall always be moist, as the friction would otherwise hurt it, and the subsequent addition of water would be liable to cause a fracture. The final polishing is done on a wooden wheel with tripoli, or by means of a leather buffer with tripoli or rouge. (Kunz, "The Occurrence and Manipulation of Rock Crystal.") |
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Precious Stones Guide Vol 9
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