Feasibility study on color evaluation of jadeite based on GemDialogue color chip images

Abstract

Through the calculation of gemological chromaticity, the green characters and range of chromaticity of 728 cabochon jadeite jade were determined, and then it studies and compares with GemDialogue color card images for jadeite-jade green quality evaluation. It is testified that the method is proved to be effective and the construction of emerald green quality grading system based on it is proved. First of all, with reference to China national standard GB/T 23885-2009 "Jadeite-jade Grading," the color appearance of jadeite-jade color green was analyzed contrastively with the help of three pieces of GemDialogue color chip images G, Y2G, and B2G where CIE recommended standard light sources D65, A, and CWF, and then it is proposed that the best light source of jadeite-jade color green measuring and evaluating is standard D65 based on quantitative analysis of samples' lightness L * , chroma C * , hue h 0. Secondly, according to samples color green and five pieces of GemDialogue color chip images G2Y, Y2G, G, B2G, and G2B, jadeite-jade color was graded in seven levels from the best end "Fancy Vivid" to the last end "Very Light" with the contribution of five different overlap modes of three color masks: black/gray transparent, brown transparent, and black/white opaque. Furthermore, the high accuracy of the method is verified by clustering analysis and Fisher's discrimination reversely. It draws conclusions that there are two evaluation methods of jadeite-jade color green; the first is the colorimetric way of GemDialogue color chip images, and the complementary is the way of Fisher functional method which sample parameters could be back substituted, and all these two methods could be extended to other green gem quality evaluation.

Study on the effect of heat treatment on amethyst color and the cause of coloration

“…Based on CIE1976 L*a*b* uniform color space system, the classification uses two mathematical methods: K-means clustering analysis and Fisher discriminant analysis. These two methods have been verified in peridot 24,25 , tourmaline 26,27 , jadeite [29][30][31] and other colored minerals. K-means Cluster analysis is a statistical analysis technology that divides the research objects into relatively homogeneous groups.…”

“…In this method, the colored diamonds were graded in standard illumination box and a 6504 K fluorescent lamp was used as lighting source. Then the International Commission on Illumination (CIE) 1976 L*a*b* uniform color space system has also been gradually applied to the mineral color evaluation and grading system, such as sapphire 19 , alexandrite 20 , 21 , color change garnet 22 , 23 , peridot 24 , 25 , tourmaline 26 , 27 , citrine 28 and jadeite 29 – 31 . However, there are few studies on the color evaluation and analysis in the process of heat treatment of amethyst.…”

Impact of different standard lighting sources on red jadeite and color quality grading

“…The spectral radiation of red zone is the strongest in the visible light region with color-rendering index (Ra) up to 92.39. Importantly, the input of orange-red color makes it suitable for illuminating red jadeite (Guo, Zong, Qi, Zhang & Wang, 2018c). The spectrum curve under D65 light source is uniform in green, yellow and red zone with the highest peak in the blue-green zone at 480 nm.…”

Color effect of light sources on peridot based on CIE1976 L*a*b* color system and round RGB diagram system

“…The color of peridot was first quantified by Stockton and Manson based on the CIE1931 color space system in 1983, but the geometrical distance between two colors is inconsistent with the human visual perception in the system. In order to solve this problem, the CIE1976 L*a*b* uniform color space system was established and applied to gem color research, such as peridot, alexandrite, sapphire, tourmaline, color‐change garnet, rose quartz, Cubic Zirconia (CZ), blue amber, citrine, and jadeite‐jade …”

“…In order to solve this problem, the CIE1976 L*a*b* uniform color space system was established and applied to gem color research, such as peridot, 7 alexandrite, 8,9 sapphire, 10 tourmaline, 11,12 colorchange garnet, [13][14][15][16] rose quartz, 17 Cubic Zirconia (CZ), 18 blue amber, 19 citrine, 20 and jadeite-jade. [21][22][23][24][25] However, the shape of the a*-b* diagram is distorted in the CIE1976 L*a*b* color space system. Hue angles are not evenly arranged in the a*-b* diagram, so we cannot judge which hue angle is yellow or green from the diagram.…”