Spotlight on Cobalt Blue
Until the nineteenth century the best blue pigment available to artists was ultramarine. Laboriously ground from lapis lazuli, a semi-precious stone mined only in distant Afghanistan, the prohibitive costs of this pigment prompted the Napoleonic administration to find an alternative. The chemist Louis-Jacques Thenard was commissioned by the French interior minister, Chaptal, himself an industrial chemist, to develop a synthetic substitute for ultramarine.
Thenard knew the famous Sevres potteries used salts containing cobalt (smalt) to produce their blue glazes, and in 1802, from a mix of cobalt salts and alumina, he produced a pigment called cobalt blue. With a purer tint than Prussian Blue, it was immediately taken up by artists.