Coal Black is an opaque, slick obsidian glaze that boasts a glossy, smooth surface after firing. 100% mixable and true to their unfired color, the Teachers Palette glazes are a must-have for any classroom or studio. Also try using using Cotton (TP-11) as a base glaze and, using any of the other Teacher's Palette colors, brush on colorful designs and patterns reminiscent of majolica ware.