Study Of Viewing Surrounds And Color Grading Of Peridot

This research investigates the most effective light source,illuminance and background for grading peridot's color.EMPA,spectrophotometer,UV-vis and CAM16 color appearance model were used to test and grade the color of peridot.Peridot's color is dominated by selective absorption of visible light caused by Fe²⁺that its hue angle is in an inverse ratio of the concentration of Fe²⁺.The color effect of peridot under different standard light source was studied based on CIE1976 L^*a^*b^*color space system and round RGB diagram system.It suggests that the spectral power distribution and color temperature of standard light source significantly influence the color of peridot in terms of lightness and chroma,particularly in hue of peridot.As for color grading and displaying of peridot,standard light source A fails to fit in and the color of peridot under fluorescent light source has higher chroma but lower hue angle than that under daylight light source.The results of illuminance experiments suggest Hunt effect,Stevens effect as well as Bezold-Brücke hue shift fits in peridot and the illuminance 2500 lx performs best for displaying.Backgrounds significantly influence the color of peridot.Gold alloy backgrounds are not suitable but Munsell N9 background seems to be the most effective background for peridot color grading.The color appearance of peridot will be brighter and more vivid when the luminance is increased,which corresponding to Hunt Effect and Stevens Effect.Viewing surrounds mainly influence the lightness and brightness in color appearance of peridot.CAM16 color appearance model maybe not apply to predict the effect of light source on color appearance of peridot due to the metameric effect.The windowing issue and the facets in peridot should be taken into consideration during prediction calculation.The most effective viewing conditions should be D₆₅ light source,2500 lx and Munsell N9 background.Under these conditions,peridot's colors were graded into three levels,from good to bad,Fancy Intense,Fancy Deep and Fancy by using K-means clustering analysis and Fisher discriminant analysis methods.The peridot's color level reverse phenomenon should be considered when the backgrounds varies between Munsell N7 and N9 gray.