Cobalt dyes

Smalta - cobalt blue glass grated into powder
Used often in the Renaissance instead of ultramarine.

Cobalt blue - cobalt blue - cobalt aluminate
Formed by depositing cobalt salts on clay at 1100oC.
Invented in the 19th century. Resistant to light, used in all techniques. Not sensitive to combinations. Combines well with oil (takes 14% of it).
Good opacity. Accelerates drying and serves as a siccative for other dyes.
Because of the speed of drying, cracks in the paint layer are formed.
Recognition:
Acids and alkalis do not affect it.

Cobalt green - cobalt zincate
It is formed by the deposition of cobalt nitrate on zinc white at 1100oC. Bright, cool green hue. Moderately durable. Not used in alkaline binders. Medium coverage. Dries well in oil.
Recognition:
In concentrated hydrochloric acid, when heated, gives a pink solution.

Ceruleum - a combination of cobalt and lead salts
Light blue. Absolutely permanent, used in all techniques.

Cobalt violet - cobalt phosphate.
Used in all techniques (has properties like other cobalt dyes).

Aurealin - cobalt nitrate
Laser-like, light yellow. Resistant to light. It does not tolerate combinations with zinc white and therefore in oil and tempera techniques rather not used. In watercolor it behaves well, but under glass it blackens.