Quantitative Study On Color Classification Of Diamond

The color-grading of diamond is the key factor to evaluate the value of diamond.At present,the methods of color-grading are:colorimetric method,color memory method,etc.These methods are greatly influenced by external and human factors.the content of this thesis is to study the feasibility of quantitive grading of diamond color by infrared spectrum and ultraviolet visible spectrum.Through infrared spectrum analyses,founded that the intensity of the absorption peak at 1363¹370 cm^-11 and 1010 cm^-1 monotonically increaseed with diamond grade shift to lower side,and both peaks showed a good trend of monotonicity,but peak at 1010 cm^-1 is better.Peak at 1363 cm^-1 indicates platelets contributes to diamond color,and peak at 1010cm^-1 which indicates plastic deformation related to segregated nitrogen also contributes to diamond color.By calculating the intensity and area of the two absorption peaks,qualitatively analysis can be carried out.It has found that diamond's yellow color related to the defect of N3 and N2 centers.By UV-Vis spectrum,the diamond color grading is related to the intensity of the absorption peak at 415 nm and 478 nm,the intensity of 478 nm is better with the diamond color gradation.The ratio I_{415 nm}/I_{478 nm},can well reflect the gradual change related to color grading.So the color grade of diamond can be estimated according to the shape of N3 and N2 absorption peak and the ratio I_{415 nm}/I_{478 nm}.The colorimetric coordinates were obtained by measuring the UV-Vis spectrum of diamond tabletop,and the linear trend between one set of colorimetric diamonds was unsatisfactory.After average,the linear tendency is very good,the chrominance coordinate data of each color level can be separated from each other and can be used as a reference standard for quantifying diamond color grade.The“V-groove system”and the“spherical diffuse reflectance measurement system”can be located vertically and microscopically in the same position at the pavilion from the diamond base tip.By analyzing the chromaticity coordinates of the diamond pavilion,it is found that the spacing between the colorimetric levels of the complete set of colorimetric stones is not uniform,but it can show a good linear rule.Through the calibration of colorimetric stone,the chrominance coordinate value of each color level is relatively concentrated,and the color level can be analyzed quantitatively.The two color measurement systems improved by UV-Vis spectrometer both have micro-positioning devices,and can simulate the way of human eye color observation,but the illumination system is different.Both methods can be used for the quantitative analysis of color level,but due to the the inhomogeneity between the color levels of complete sets of colorimetric stones,the equal-distance model of color level and the assumption of standard color material are put forward.