Inorganic blue for high temperature

Cobalt blue is traditionally used as the primary crystal phase for CoO Al2O3 spinel.For this type of color containing Zn0 is designated sea blue.Co-A1-Si is CoO·Al2O3 spinel obtained by combining cobalt oxide with kaolinite and paraffin.The Co-Zn-Si coloration is obtained by adding ZnO and SiO2 to cobalt oxide and then fire.

In the formed silicon-zinc ore (Zn2SiO4) structure, the replacement form of Co²⁺→Zn²⁺ makes Co²⁺ solid solution in Zn2SiO4.The silica-zinc structure was maintained (about half of the Zn2⁺ was replaced by Co2⁺).Then form a reddish and purplish blue color compared with CoO·Al2O3 spinel.

The Co-Si color is the Co2SiO4 olivine formed after sintering by adding SiO2 to cobalt oxide.Cobalt remains in the Co²⁺ state in all of the above colors.To get the violet blue，it can also add a small amount of cobalt oxide to the glaze.In common commercial cobalt oxide, beside CoO, it is mixed with Co3O4[CoO·Co2O3]. Co3+ affects the blue color.After adding 1%~2%(mass percentage) of cobalt oxide to the glaze, it is impossible to disperse cobalt oxide evenly in the glaze.This is the same thing as adding Cr2O3.Therefore, only after the cobalt oxide is diluted in the glaze with SiO2 and Al2O3 as the main components, and then add it into the glaze, can Co2+ be evenly dispersed in the glaze in a bivalent state.This color  is called cyanosis.

The composition of Co-Si system color is Co2SiO4.Co²⁺ occupies all octahedral voidage, and its coordination number is 6, and its color is purplish red.Because it is bluish blue in the glaze, it is belong to the blue color.Zr-Si-V (zircon - zirconium blue) is the mainstream of blue. It is greenish compared to cobalt blue.