The CIECAM16 colour appearance model is currently a model with high prediction accuracy. It can solve the problem of predicting the influence of different observation conditions on the colour of gemstones. In this study, a computer vision system (CVS) was used to measure the colour of 59 bluish-green serpentinite samples, and the tristimulus values were input into the CIECAM16 forward model to calculate the colour appearance parameters of serpentinite under different surrounds, illuminances, and light sources. It was found that the darkening of the surround causes the lightness and brightness to increase. Pearson’s r of brightness and colourfulness with illuminance is 0.885 and 0.332, respectively, which predicts the Stevens and Hunt effects. When the light source changes from D65 to A, the calculated hue angle shifts to the complementary area of the A light source, which is contrary to the CVS measurement result. The D65 light source is more suitable for the colour presentation and classification of bluish-green serpentinite.
The Beihong agate from the southern section of the Xing’an Mountains in northeastern China is a kind of cryptocrystalline agate with a yellow to orange-red colour. However, it has been less studied in previous research, and there is a lack of quantitative study on the cause of its colour. In this study, the colour of Beihong agate was quantified by a colourimeter, and the quantitative relationships between colour and spectral characteristics of Beihong agate were studied by XRF, Raman spectra, UV-VIS spectra, and a heat treatment experiment. The results show a high correlation between the lightness and the hue angle of the Beihong agate. The change of total Fe content can significantly affect the lightness and the hue of the Beihong agate. The first derivative curve can effectively distinguish the relative contents of goethite and hematite in the Beihong agate, and the position of a primary trough is related significantly to the colour of the Beihong agate.
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