Ceramic glaze in which microscopic crystals are formed upon firing. It is made by cooling the fired object very slowly allowing crystals to form in the otherwise amorphous glass film. Under the right conditions, zinc silicate and calcium silicate form large crystals in the glaze surface. The technique was first developed at Sevrès in France in about 1850; the method is complex and difficult to produce. These glazes are different than aventurine or devitrified glazes, which may also appear to contain crystals.
