Shiratama is a type of flux, a fine powder of colorless glass used to reduce the degree of melting by mixing with base, glaze, or overglaze pigments. There are a large number of fluxing materials. Among them, water-insoluble materials, whether natural or artificial, can be mixed with water as they are, but soluble materials can never be mixed with water as they are. Therefore, such materials must be heated and melted together with other raw materials of silicic acid to form insoluble objects, i.e., white balls, which must then be mixed. Among the most commonly used raw materials today, those that must be used after transformation into white balls are borax, acids, and salts of potash and soda. To manufacture white jade, a mixture of these ingredients is made by mixing them appropriately, placing it in a heated clay crucible, heating it well, melting it, and then cooling it rapidly by throwing it into cold water to produce a fine powder. There are several types of kilns required for the production of shiratama. In Japan, lead, silica stone, and nitre are the three raw materials commonly used. The proportions vary according to the purpose. Those containing borax and boric acid are less viscous, while others are more viscous.
