underglaze

Underglaze is a method of decorating ceramic articles in which the decoration is applied to the surface before it is glazed. Because the glaze will subsequently cover it, such decoration is completely durable, and it also allows the production of pottery with a surface that has a uniform sheen. Underglaze decoration uses pigments derived from oxides which fuse with the glaze when the piece is fired in a kiln. However, because the glost firing is at a higher temperature than used in on-glaze decoration, the range of available colours is more limited. Examples of oxides that do not lose their colour during a glost firing are the cobalt blue made famous by Chinese Ming dynasty blue and white porcelain and the cobalt and turquoise blues, pale purple, sage green, and bole red characteristic of Iznik pottery.