The blue has been known since the early 19th century. It is a superb reddish blue of great permanence suitable for all media. Cobalt is an excellent drier in oil paints. Over time more and more cobalt’s have been developed from violets and blues through turquoise to greens, all of great light fastness, but some not being very strong in tinting strength. The newer cerulean shades have been excellent additions to the palette. Cobalt was never cheap but the development of the jet engine in the 1950’s sent the price through the roof, and it has stayed there ever since. Cobalt is essential in the treatment of jet turbine blades to help them withstand great heat and other stresses