 Before the 19th century , cobalt was predominantly used as a pigment . Since the Middle Ages , it has been used in the production of smalt , a blue colored glass . Smalt is produced by melting a mixture of the roasted mineral smaltite , quartz and potassium carbonate , yielding a dark blue silicate glass which is finely ground after the production . Smalt was widely used for the coloration of glass and as pigment for paintings . In 1780 , Sven Rinman discovered cobalt green , and in 1802 Louis Jacques Thénard discovered cobalt blue . Cobalt pigments such as cobalt blue ( cobalt aluminate ) , cerulean blue ( cobalt ( II ) stannate ) , various hues of cobalt green ( a mixture of cobalt ( II ) oxide and zinc oxide ) , and cobalt violet ( cobalt phosphate ) are used as artist 's pigments because of their superior chromatic stability . Aureolin ( cobalt yellow ) is now largely replaced by more lightfast yellow pigments . 
