The color parameters of 19 pieces purity transparent and color uniform commercial grade tanzanites were measured by colorimeter Color i5 and this article introduces the concept of Metamerism and calculates the color quantitatively, based on CIE1976 L*a*b* uniform color space, analysis the contribution of different illuminators to the bluish-violet color of tanzanite. The change of hue-angle h0 is in contrast to the actual visual effect, this is called abnormal hue-angle change of the gemstone tanzanite; both of the contributions of lightness difference and chroma difference play the same role to the change of the color difference, form the bluish-violet of tanzanite; it is shown that Metamerism indexes (Mt) of different samples are different and the same sample’s main wavelength follows the change while illuminators altered. Therefore, while illuminators altered, the color of tanzanite samples change from blue to bluish-violet, and the Mt larger, the change of color is greater, namely, the violet hue is more clear, with the better color appearance.
Color space analysis of mutual illumination
