Cobalt(II) oxide

Cobalt(II) oxide is a blackish gray powder used extensively in the ceramics industry as an additive to create blue colored glazes and enamels as well as in the chemical industry for producing cobalt(II) salts.

Cobalt(II) oxide is a product of Cobalt(III) Oxide decomposing at 895 °C through the reaction:

2 Co₃O_4(s) → 6 CoO_(s) + O_2(g)

Ceramics

Cobalt(II) Oxide has for centuries used as a coloring agent on kiln fired pottery, the earliest examples go back to 12th century German pottery.The additive provides a deep shade of blue named Cobalt Blue.

References

1. http://www.ceramicstoday.com/articles/zamek_cobalt.htm