Study On The Relationship Between Aquamarine Composition And Color And Color Grading

In this article,ED-XRF,UV-VIS,FTIR,Raman,X-rite SP62 colorimeter were used to study the composition and chromaticity of aquamarine.Then the standard light source box and Munsell achromatic background were used to discuss the best external environmental conditions for displaying and grading aquamarine,and finally scientific and reasonable color quality evaluation of aquamarine.ED-XRF results show that the main components of aquamarine are Al,Si,Fe,and alkali metal elements.Al³⁺replaces tetrahedral Si⁴⁺in the sample,and there is a positive correlation between Fe content and chroma.UV-VIS shows that the absorption peak caused by Fe³⁺near425nm increases the yellow tone of aquamarine.The stronger the absorption peak near 425nm,the larger the chromaticity value b^*,which shows that the yellow tone of the sample increases;the absorption band near 620-700nm and Fe²⁺Related,the wider the absorption band,the smaller the chromaticity value b^*,which is manifested as an increase in the blue tone of the sample;the absorption band near 810nm is caused by the Fe²⁺electronic transition,and the absorption band in the sample blue shifts to 760nm,causing absorption of red,increasing up its green hue.On the basis of differential thermal analysis,through the study of infrared spectroscopy,it is found that there are two types of water inside the aquamarine,which begin to escape when heated to above500?.During the heating process,there is[Fe(H₂O)]₆³⁺located at the C₁position in the channel.The reduction of content shifts 1200cm^-1to the low band.Raman spectroscopy analysis shows that the sample is low-alkali beryl,and type I water is dominant.The larger the ratio of type I water to type II water,the smaller the sample chromaticity value a^*,and the hue tends to be green.The larger the type-water ratio,the smaller the sample chromaticity value b^*,and the hue tends to be blue.Aquamarine has the characteristics of high brightness and low chroma.Under different standard light sources,the hue and chroma of aquamarine have significant differences.The chroma value is the highest under the standard A light source and the smallest under the standard CWF light source.Therefore,the standard A light source is suitable as a display light source for aquamarine;under the standard D65 light source,the hue angle difference is the largest and the color discrimination is high.Therefore,the D65 light source is suitable for aquamarine Color grading;samples with brightness greater than 80 and chroma greater than 8 are significantly affected by the light source.Through testing and analyzing the influence of achromatic backgrounds with different gray levels and standard silver jewelry backgrounds on the color of aquamarine,it is found that as the background gray level decreases,the lightness of the aquamarine increases,the chroma increases,and the hue angle is basically unchanged.The color appearance has been improved;aquamarine has a low chroma discrimination under a dark background,and a high discrimination under a bright background.The N9 background can magnify the difference in the color of aquamarine,which is suitable for aquamarine grading background.Through the above discussion,it is concluded that the environmental conditions suitable for color grading of aquamarine are standard D65 light source and Munsell achromatic N9background.Using the mathematical analysis method of K-means rapid clustering,the faceted aquamarine is divided into three from inferior to superior.Grade:Blue,Intense Blue,Vivid Blue.Then use Fisher discriminant analysis method to discriminate and verify the accuracy of 100%,which proves that the classification method is scientific and effective.