Considerably low values of all the colour coordinates can be explained by insufficient processing of the raw material and formation of multiphase systems (1300 C). Table 1 lists the pigments with Tb concentration x ¼ 0.3. The concentration was chosen as the pigments in this concentration show the brightest yellow colour. Increasing the calcination temperature leads to considerable shift in tones and primarily to enhancement of the yellow tone in all analysed pigments. The biggest change was recorded for the pigments calcinated at 1500 C. Over 1300 C, the
pigments obtained slightly reddish tone. Increasing values of colour coordinates (L*, a*, b*) correspond to increasing calcination temperature. Pigment calcinated at 1600 C manifests a slight decrease of the L* a* b* coordinates.