QUANTITATIVE EVALUATION OF THE COLOUR OF GEM STONES WITH ALLOCHROMATIC COLOUR

The purpose of the work: development of a method that will allow us to determine the quantitative indicators of some colour characteristics of gem stones. Methodology of the research: the study of the absorption spectra of gem stones, the identification of patterns and the development of mathematical tools for quantitative estimate the lightness parameter. Results. The dependence of the lightness of a gemstone is established by the relative magnitude of light absorption in the zone of the absorption band caused by the main element-chromophore. Mathematically, the characteristic proportional to the optical density of the gemstone is determined, which can be used to quantify its lightness. The nonlinearity of the scale of this characteristic is shown in comparison with the colour groups or lightness indicators accepted in Russia and the USA. Examples are given that reveal the approaches to quantifying the colour of various gem stones with allochromatic colour. Conclusion. Measurement of the spectral characteristics of gem stones allows us to quantify the indicators of their lightness. For the practical application of this technique, it is necessary to determine the colour standards and the subsequent graduation of the scale. The accuracy of measurements depends on several factors; the main being the sample size. To improve the accuracy of determining the lightness of large gem stones, it is necessary to increase the number of measurements