Gemological Characteristics Of Lazuli Lapiz And Colorimetry Charaterization Of Its' Blue Color

Lapis lazuli has a long history as a kind of precious gem.The colors of lapis lazuli have a widely range.Among all the color of lapis lazuli,"Bright Azure" and "Ultramarine Blue" are most unique and have highest value.It is urgent to make a color grading system for lapis lazuli since the demand of lapis lazuli in the current market is increasing fast.In this research,the gem characteristics of 30 natural lapis lazuli have been study,including refractive index,specific gravity,observation under the Charles Filter,ultraviolet fluorescence and the gemological microscope.Also we have compared the characteristics of imitations and natural lapis lazuli.The spectral characteristics of lapis lazuli were invest igated by Ftir and UV-vis spectroscopy.Relationship between the feature absorption and the blue color of lapis lazuli was analyzed.60 group tristim ulus and CIE1976L*a*b* color parameters of lapis lazuli have been measured by Color i5 measurement instrument.The tristimulus values were used in the CIECAM02 color model at the following part in this paper.The blue color of lapis lazuli were described in the CIE1976L*a*b* color space under the D65 light.We applied CIECAM02 color appearance model to predict the change of lapis blue color in different observation conditions,and set up three simulation observation experiments,under different illumination,surroundings and illumination light source conditions,predicted the change of lapis blue color.Finally,we compared the experimental results in CIECAM02 and CIE1976L*a*b* color space,evaluated the color model of lapis lazuli by Munsell Color Order System observation.