It is extremely stable and historically has been used as a coloring agent in ceramics (especially Chinese porcelain), jewelry, and paint.

Ores containing cobalt have been used since antiquity as pigments to give a blue color to porcelain and glass.

[1] In 1742, Swedish chemist Georg Brandt showed that the blue color was due to a previously unidentified metal, cobalt.

Germany also was famous for production of it, especially the blue colour works (Blaufarbenwerke) in the Ore Mountains of Saxony.

Art Automobiles Construction Sports Vexillology Video games Cobalt blue is toxic when ingested or inhaled.