Cobalt oxide (CoO or Co3O4) is a consistent, reliable oxide and a common colorant in pottery. It is available in powdered form and is blackish in color. It is a very strong oxide, and using very small quantities yields bright, intense blues. In ceramics, cobalt oxide is used mainly in slips, 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. Because cobalt oxide is not as finely powdered as cobalt carbonate, cobalt oxide is more likely to create blue specks, a quality that we believe can be quite beautiful!
Because of the strength of this oxide as a colorant, glazes containing cobalt can produce halos and flashing during firings. Suggested concentrations for preparation of slips and glazes are as follows:
In slips: 0.25 - 2%
In glazes: 0.25 - 1%
When mixed with magnesium in the proper concentrations, cobalt oxide can produce purples and lavenders. When properly combined with titanium, greens can result. Additional colors and effects can be achieved using cobalt oxide, and we recommend that you consider consulting some of the many wonderful glaze books available.
In its powdered form, Cobalt oxide can be very hazardous if ingested and can cause skin, eye and/or respiratory system irritation. Please use proper precautions, including protective coverings, when working with this substance. If inappropriate contact does occur, seek medical attention immediately.
WARNING: This product can expose you to chemicals including Cobalt Oxide, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.