• (n.) A greenish blue pigment prepared in various ways, consisting essentially of cobalt stannate. Unlike other cobalt blues, it does not change color by gaslight.
Ce·ru'le·um noun [ New Latin ] A greenish blue pigment prepared in various ways, consisting essentially of cobalt stannate. Unlike other cobalt blues, it does not change color by gaslight. 
Ceruleum is a blue pigment, consisting of stannate of protoxide of cobalt mixed with stannic acid and sulphate of lime.Ceruleum is a blue pigment, consisting of stannate of protoxide of cobalt mixed with stannic acid and sulphate of lime.