A mineral CaCO3MgCO3 Dolomite is mainly used in stoneware glazes (temperatures about 1175&176;C or 2174&176;F). There are other suitable sources of calcia, but insoluble magnesia is less common. Dolomite acts as a flux but, if used to replace whiting, it will raise the maturing temperature of a glaze. Average proportion in a glaze is 3 6%, but up to 20% can be used for special effects. The typical magnesia effect derived from the use of dolomite is a smooth, buttery surface. With higher concentrations and slower cooling, however, it tends to form crystals of calcium and magnesium silicates with a consequent matt surface. - p. 88, Illustrated Dictionary of Practical Pottery, 3rd Ed. by Robert Fournier
50# bag; brown bag, blue text Limestone and Specialty Minerals
