GLAZE - For pottery.
Glaze in pottery works as a varnish does for furniture, except that it has to be fired. In some parts of Spain it is called varnish. It is a finely ground mixture of minerals and industrially made powders such as silica, alumina and flux, prepared to melt at different temperatures.
Glaze is bought prepared as a powder and is one of the most important products used in pottery. Traditionally lead oxide was used, but this is now illegal due to health reasons. Tin oxide is currently the main ingredient for glazes, this product being developed for its whiteness and opacity. There are many different types of glaze-bases made up with different formulas and textures, matte, semi-matte and crackle, etc. and all can be purchased ready-made.
To use, it is mixed with water. put on to clay or bisque and when fired, it melts and turns into a transparent, thin, layer of glass that can be shiny or matte. The natural color of the bisque or clay reflects through the glaze giving it a strong, attractive quality. The glaze makes the work non absorbent to liquids and the process is known as glaze firing.