A majority of dye pigments are derived from metals. Red dye comprises mercury sulphide, cinnabar and vermilion, yellow dye uses cadmium, while blue dye is made from cobalt salts. Other colours are made from chromium, manganese, ferric oxide or zinc oxide. Black dye is non-metallic and is made from carbon, black ink or logwood. Most of the metallic dyes are harmful to the skin.