Cobalt colours are, perhaps, the most diverse “family” used in the production of contemporary artists’ colours. Depending upon the element combined with Cobalt a wide range of highly stable colours are possible. For example, Cobalt Stannate (tin) makes Cerulean. Cobalt Aluminate (aluminum) makes Cobalt Blue, and Cobalt combined with nickel, titanium, and zinc oxide yields Cobalt Green. All are known for exceptional stability and lightfastness.
It’s history dates back to antiquity, when Cobalt was ground and fired into glass. After being crushed, the blue glass was used as pigment (Smalt). Modern cobalt pigment compounds date to 1780 (Cobalt Green), followed by Cobalt Blue in 1802.
All Cobalt colours tend to offer great depth in mass-tone with a range of subtle and compelling qualities in undertone. In water colour, all are strongly granulating.

Cobalt Aluminate, PB28
AA – Extremely Permanent; ASTM I
Series 4
Semi-Transparent