Sven Rinman, a Swedish chemist, discovered this compound in 1780.
It is rarely used because it is a weak chromophore and relatively expensive compared to chromium(III) oxide.
For x ≤ 0.3, the material adopts the Wurtzite structure (of ZnO) and is intensely green.
For x ≥ 0.7, the material has the sodium chloride structure (of CoO) and is pink.
Cobalt green is attractive in this application because it is magnetic at room temperature.