Cobalt blue is widely used as coloring agents in ceramics, glassware, and plastic products, etc., due to the chemical and thermal stability. In this study, the influence of mixing time and calcination temperature on the color tone of cobalt blue was investigated. Cobalt blue particles were synthesized by the solid phase reaction method with cobalt oxide （Co3O4） as Co source and aluminium hydroxide （Al（OH）3） as Al source, respectively. The obtained powders were characterized by CIE-L*a*b* color space, particle size distribution, SEM-EDX, and XRD. The chromaticity coordinate b* of the calcinated powder was shifted to blue direction, and the chroma represented by c* became vivid with increasing calcination temperature. This means the color tone of the cobalt blue powder becomes vivid blue. However, the color tone of the calcinated powder barely changed even if the mixing time of raw materials was increased. XRD analysis of the calcinated powder revealed the formation of the single-phase CoAl2O4 at 1200 ℃. These results indicate that the color tone of cobalt blue is mainly controlled by the calcination temperature in the solid phase reaction method.
