Mason Stains ® (by Mason Color Works) are colorants in frit form, which renders them insoluble, removes volatiles, and allows for better control of final product. When used as a glaze stain, we generally recommend adding the stain at 5-8% dry weight to a dry base glaze. The base glaze should contain 12-15% calcium carbonate (whiting) and be free of zinc to achieve the color desired. Mason Stains can also be painted on bisque as an underglaze. Experimentation is necessary to achieve the desired results, but the advantage of Mason Stains is their consistent results in glaze firing.