QUANTITATIVE EVALUATION OF THE COLOUR OF GEM STONES WITH ALLOCHROMATIC COLOUR

Roman Nikolaevich ZUBOV

R. N. Zubov / News of the Ural State Mining University. 2018. Issue 4(52), pp. 50-56 

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.

Keywords: gemology, gem stones, spectrometer, absorption spectrum, light absorption, colour hue, lightness, chromophore.

REFERENCES

1. Bukanov V. V. 2008, Gemstones. Encyclopedia. Saint-Petersburg, 416 p. http://gems.minsoc.ru
2. Nassau K. 1997, Color for science, Art and Technology. Vol. 1. Amsterdam: Elsevier, 490 р. https://www.elsevier.com/books/color-for-science-art-and-technology/nassau/978-0-444-89846-3
3. Darby Dyar M. Color in minerals. USA: West Chester University, 348 p. URL: http://www.minsocam.org/msa/monographs/Mngrph_03/MG003_323-348.pdf
4. Tani S., Fukunaga Y., Shimizu S., Fukunishi M., Ishil K., Tamiya K. 2012, Color standardization method and system for whole slide imaging based on spectral sensing. Analytical Cellular Pathology, vol. 35, issue 2, pp. 107–115. http://dx.doi.org/10.3233/ACP-2011-037
5. Bacik P., Fridrichova J., Stubna J., Antal P. 2015, Application of spectroscopic methods in mineralogical and gemmological research of gem tourmalines. Acta Geologica Slovaca, vol. 7(1), pp. 1–9. URL: http://geopaleo.fns.uniba.sk/ageos/archive/2015_01/bacik_et_al_2015.pdf
6. Reddy J., Frost R., Martens W., Wain D., Kloprogge T. 2007, Spectroscopic characterization of Mn-rich tourmalines. Vibrational Spectroscopy, vol. 44, pp. 42–49. https://doi.org/10.1016/j.vibspec.2006.07.010
7. Merkel P., Breeding C. 2009, Spectral differentiation between copper and iron colorants in gem tourmalines. Gems and gemology, vol. 45, Summer, pp. 112–119. URL: https://www.stellarnet.us/wp-content/uploads/G-and-G-Article.pdf
8. Xueyang L., Ying G. 2016, Color grading of emerald green based CIE 1976 L*a*b. 2nd International Conference on Economics, Social Science, Arts, Education and Management Engineering (ESSAEME 2016). Beijing: China University of Geosciences, pp. 818–826. URL: https://download.atlantis-press.com/article/25860334.pdf
9. Konovalova A. N. 2011, Analiz tsveta turmalinov dlya dizayna yuvelirnykh izdeliy [Color analysis of tourmaline for jewelry design]. PhD thesis. Irkutsk, 155 p.
10. Vasilyev E. A. 2013, Registration of the faceted gems absorption spectra. Journal of Mining Institute, vol. 200, pp. 163–166. URL: http://pmi.spmi.ru/index.php/pmi/article/download/732/760
11. Royen J., Loots I. Automatic color grading. WTOCD, Lier, Belgium. URL: http://www.wtocd.be/nl/Projects/lumisense_auto_color.html
12. Ertl A., Kolitsch U., Dyar M., Hughes J., Rossman G., Pieczka A., Henry D., Pezzotta F., Prowatke S., Lenganer C., Korner W., Brandstatter F., Francis C., Prem M., Tillmanns E. 2012, Limitations of Fe2+ and Mn2+ site occupancy in tourmaline: Evidence from Fe2+ and Mn2+- rich tourmaline. American Mineralogist, vol. 97 (8–9), pp. 1402–1416. https://doi.org/10.2138/am.2012.4028
13. Lopatin O. N., Nikolaev A. G., Khaibullin R. I. 2012, Crystal-chemical aspects of the ionic implantation of minerals and their synthetic analogs. Zapiski RMO [Proceedings of the Russian Mineralogical Society], Part 141, issue 1, pp. 61–70. URL: https://elibrary.ru/item.asp?id=17674662
14. Kropantsev S. Yu. 2000, Chromium andradite from the Novo-Karkodinskoe deposit of demantoid garnets. Izvestiya UGGU [News of the Ural State Mining University], issue 10, pp. 72–77. (In Russ.) https://iuggu.ru/download/10zip.pdf
15. Kleismantas A., Dauksyte A. 2016, The influence of Vietnam and Sri-Lanka spinel mineral chemical elements on colour. Chemija, vol. 27, no. 1, pp. 45–51. URL: http://mokslozurnalai.lmaleidykla.lt/publ/0235-7216/2016/1/45%E2%80%9351.pdf
16. Kiselev R. K. 2012, The need to update the evaluation system color cut stone. Nauchnyy vestnik Moskovskogo gosudarstvennogo gornogo universiteta / Gornye nauki i tehnologii [Mining Science and Тechnology], no. 9, pp. 30–37. (In Russ.) URL: https://elibrary.ru/item.asp?id=17964606