A melting or fluxing agent. Used to adjust the melting properties of a glaze and to give it the required translucency. The choice of flux is important, since the action of the fluxing agent varies with the base used. It is advisable to use two or three different oxides as the base. This is because they form a co-melt, which is stronger and more effective than using the same amount of a single melting agent.
In order to improve the fluidity, luster, mechanical strength, and weathering resistance of glazes, or to take into account their specific effects such as the coefficient of thermal expansion of the glaze and the coloration of pigments, alkali or Ajyu Kiakuan’s non-yuwa-ring celadon with floating flowers in the ears, shinchu lucali earth oxides are often used. In Japan, various types of wood ash or lime were commonly used in the past. (Ceramics for Crafts)