Duncan Cover Coats glazes. Applied directly to greenware, soft-fired bisque or bisque, these underglazes provide solid coverage over even the darkest colors, and are perfect for airbrushing and brushwork. Cover-Coats¨ fire to an opaque, porous matte finish and are safe for food when a Duncan food-safe clear glaze is applied over them. For custom colors, tint them with other Cover-Coat¨ Underglazes or E-Z Strokeª Translucent Underglazes.