A glaze in which a portion of the glaze component crystallizes during cooling from the molten state during firing. When the crystalline form is extremely small, it becomes an aventurine glaze or a mat glaze. The existence of glazes with crystalline precipitates alone can be traced back to ancient Japanese pottery and stoneware glazes made with large amounts of iron sand, but the crystals are indistinct or minute in each case, so they are hardly what we would call crystalline glazes today, in which crystals are used to create mottled patterns. The use of crystalline glaze is extremely new: Eberlemen began researching crystalline glaze around 1850, followed by Roth and Dutailly, and in 1885 their products were exhibited at the Segel Porcelain Manufactory in France, but crystalline glaze was not widely used yet. In 1894, the Rookwood Pottery in Cincinnati, Ohio, exhibited crystal-glazed ceramics at the World’s Columbian Exposition in Chicago, U.S.A., which attracted public attention, and in 1895, the next year, the company began to produce crystal-glazed ceramics in Copenhagen, Denmark, followed by Berlin, Germany, and Sevres, France. In Japan, Gosuke Kato of Seto discovered manganese crystal glaze by chance in 1897 (Meiji 30), and passed it on to Shigeru Kato. Shigeju and Kozan of Shinano worked on its development, and later this method was passed on to Hansuke Kato of Seto through Nobutoshi Inoue in Kyoto. In 1899, Yaichiro Kitamura of the Kanazawa Technical School conducted research on manganese white crystals and variations in the size, coarseness, density, and shape of crystal-colored mottling, and succeeded in producing a variety of crystal glazes. At the same time, Yanase Masatoshi explained that zinc was the cause of crystals in glazes made with Aizu whetstone, and Fujisaki Seiri of Kozuki-mura, Toyoura-gun, Yamaguchi Prefecture (Kozuki Town, Shimonoseki City) produced zinc crystals called seiri-yaki in the late Meiji period. From the late Taisho Period to the early Showa Period, Kondo Seiji of the Tokyo Institute of Technology studied various crystal glazes made of iron, zinc, manganese, and titanium, and produced a number of excellent crystal glazes. Since then, titanium crystal glazes have been widely used.
