The cobalt coloring materials used throughout Chinese history include pigments, glass and ceramic glazes. Smalt and cobalt blue are historical pigments. The application of cobalt blue glass may have started during the Western Han Dynasty. The use of cobalt blue ceramic glazes started with glaze bead of pottery body during the Warring States period and further developed into several types in tri - colored glazed pottery during the Tang Dynasty. Both domestic cobalt ore materials and imported Smalt materials were used. Contaminating components in the ore, e. g. , Mn, Fe, Ni, As and Bi, will affect the quality of cobalt coloring materials.