A pinkish tan to purple-ish powder. It is a strong colorant and almost always produces blue in glazes (unless in very high percentages where it is black). Cobalt carbonate is an extremely active melter (even more than cobalt oxide), in a mix of 50% Ferro frit 3134 it will boil at cone 6. The carbonate form of cobalt is very fine grained and disperses better in the glaze slurry and the glaze melt, it gives a more evenly distributed color than cobalt oxide. However, as with any carbonate, it produces gases as it decomposes and these can cause pinholes or blisters in glazes if they need to escape at the time when the glaze needs to solidify. The carbonate form contains less CoO (63% CoO vs. commercial cobalt oxide which is not actually 100% CoO but around 93%). Supplies of this material often differ in the shade of the raw powder (lighter and darker). This is because available grades of Cobalt Carbonate are not actually CoCO3 but a mix of the carbonate and the hydroxide. Cobalt II carbonate theoretically would have the formula: CoCO3.3Co(OH)2.H2O.