Factors Influencing The Color Of Green Nephrite And Its Quality Evaluation

In this paper,75 spinach green,duck egg green and apple green nephrite samples were selected to test the color of green nephrite by using the X-Rite SP62 integrating sphere spectrophotometer,and the color parameters of green nephrite were obtained.In CIE1976L~*a~*b~*uniform color space,combined with the light source,background,thickness and composition test,the influencing factors of green nephrite color were analyzed,and the color of green nephrite was evaluated and divided into quality grades.It can be concluded from XRF,XRF and EPMA tests that the main minerals contained in the different colors of green nephrite are all tremolite,some of them have transitioned to actinolite,the minor minerals contain chlorite and chromite,which is consistent with the X-ray powder crystal diffraction results.Then,the black dotted and banded inclusions in the green nephrite can be determined as chromite.LA-ICP-MS test results show that the content of color-causing metal elements such as Fe,Cr,Ni and Mn is high,and the content of Fe shows a negative correlation with the luminosity L~*and color C~*of green nephrite,and as the content of Fe increases,the luminosity L~*and color C~*of green nephrite show a decreasing trend,and the effect on the color is more significant,and it shows more intense color of green nephrite on hand specimens.From the UV-visible spectrum,it is clear that Cr is the main cause of the vivid green color of green nephrite,forming UV-visible absorption peaks at 660 nm and 692 nm.The higher the Cr content,the more vivid the green color of the green nephrite,and the lower the Cr content,the heavier the gray tones of the duck egg green nephrite.This paper focuses on three external factors that affect the color of green nephrite,observing how the thickness,light source,and background changes play a role in changing the color of green nephrite.From the experiment,it is clear that as the thickness of green nephrite increases,the color and brightness gradually decrease and the hue angle h_o gradually increases,and when the thickness reaches 4mm,the brightness and color tend to level off,and when the thickness reaches 12mm,the hue basically remains the same;studying the change of light source shows that the green nephrite has the highest color and moderate brightness under D65 light source,which is more suitable for green nephrite lighting,and the green nephrite is less colored and darker under A light source.Therefore,D65 is the best lighting source for green nephrite;the effect of non-color background on green nephrite luminosity and chroma is not significant,but only when the background luminosity difference is large(ΔL~*=81.42),the effect on green nephrite hue is large,and when the background luminosity difference is similar,when the non-color background brightness value is higher,the more significant the effect of background on green nephrite hue.K-Means cluster analysis in SPSS software was used to classify green nephrite color,and the best classification was achieved when green nephrite color was classified into 9 levels(test accuracy of 100%).The spinach green-apple green series of green nephrite was ranked from best to worst:Ⅰ yellow-green,Ⅱ intense yellow-green,Ⅲ light yellow-green,Ⅳ yellow-green,Ⅴ intense yellow-green,Ⅵ dark yellow-green;for duck egg green nephrite,the best was Ⅶ,followed by Ⅷ and Ⅸ in that order.