An opaque white glaze applied over a soft porcelain or stoneware base, defined as a raw glaze containing zinc oxide and fired at the same temperature as the base and glaze on a raw Stoneware base. Today, however, there are transparent and milky glazes, and the name bristle is used for colored glazes, but a true bristle glaze consists of zinc oxide, potash, lime, alumina, and silicate, sometimes with magnesia or barium oxide, but never with lead oxide. The great advantages of this glaze are that it is inexpensive, does not use lead compounds, and can be safely applied to raw substrates. Zinc oxide is added in considerable quantities to increase the opacity of the glaze and make it easier to melt, but it is not often used in porcelain glazes because it volatilizes at high temperatures. Since Bristol glazes are mainly made in the raw, a large amount of clay and kaolin is used in glaze formulation. This is why it is widely used for architectural clay products. The viscosity of the melt is high, so it can be fused to the substrate without flowing down. Generally, this glaze is used in the range of S.K 5 to 9, but even glazes with S.K 3 can be made. It can also be used to lower the firing temperature, since it is not affected by the much longer firing time. (“Ceramics for Crafts”)
