Color Evaluation Of Yellow To Green Serpentine Jade From Xiuyan,Liaoning Province

The color of 92 serpentine jade samples was quantitatively characterized by CIE1976L*a*b* color space.We carried out color evaluation and grading,and discussed internal and external factors which can affect the color.The mineral species of samples were determined to be antigorite by FTIR,Raman spectroscopy and XRD analysis.Combined with the analysis of UV-Vis spectroscopy,it is determined that serpentine jade is colored by Fe.With the increase of Fe,the luminance decreased,the hue angle increased.We studied the color difference of serpentine jade under three standard light sources D65,A and F2.We found that D65 light source is conducive to the appearance of green color and transparency of serpentine jade,thus can be used as display light source.A light source is suitable for yellow serpentine jade lighting.Due to the fact that D65 source has relatively uniform spectral power distribution and is similar to natural daylight,it is suitable for color evaluation.The color difference of serpentine jade on 9 Munsell neutral background is discussed.As the background luminance increases,the luminance of serpentine jade increases,and the hue shifts to the yellow area.For medium-chrominated serpentine jade,the chroma of the serpentine jade increases with the increase of the background luminance factor;for the serpentine jade with lower chroma,the background luminance increases,the color increase first and then decrease.It was pointed out that the content of water has an effect on the color of serpentine jade.After water absorption,the luminance and chroma of the serpentine jade are improved,and the hue shifts toward the green area.This is due to the presence of cracks or impurities in the serpentine jade.After water absorption,water enters the micro-cracks and the interstices of the particles,improving its transparency and color appearance.As the sample is exposed to the air,these absorbed water is removed from the micro-cracks and particle gaps,so the luminance and chroma of serpentine jade decrease,and the hue shifts toward the yellow area..The color evaluation of serpentine jade mainly includes three aspects: the color is best in green,higher chroma is better,and the luminance is best in medium range.Using cluster analysis and discriminant analysis,serpentine jade is divided into three series: yellow,yellow green and green.Then the serpentine jade is subdivided into 7 categories according to chroma and luminance.