Cobalt oxide (CoO or Co3O4) is a stable, reliable, and colorful oxide common in pottery. It is available in powder form and is black in color. It is a very strong oxide. In ceramics, cobalt oxide is mainly used in liquid clays, washes, and glazes and can be applied through brushwork, decals, or other surface decorating techniques. It can also be added to porcelain or stoneware clay. Since cobalt oxide is not a fine powder like cobalt carbonate, cobalt oxide is more likely to create blue spots, a quality that we think can be very beautiful! Because of this oxide's power as a colorant, cobalt-containing bottles can produce flicker halos during burning. Suggested concentrations for preparing glazes are as follows: In slips: 0.25 - 2% In glass: 0.25 - 1% When mixed with magnesium in appropriate concentrations, cobalt oxide can produce purple and lavender. When combined properly with titanium, it can produce green. Additional colors and effects can be achieved with cobalt oxide, and we recommend that you consider consulting some of the many great polishing books available. In powder form, cobalt oxide can be very dangerous if ingested and can cause skin, eye, or respiratory irritation. Please use appropriate precautions, including protective covers, when working with this material. In the event of inappropriate contact, seek medical attention immediately. Warning: This product can expose you to chemicals including cobalt oxide, which can cause cancer.