The Colorimetric Study Of Southern Red Agate

Nanhong agate has been favored by consumers because of its traditional Chinese red color and delicate texture.In recent years,the trading market has prospered.On the basis of previous research,this paper analyzes the color elements of Nanhong agate using conventional gemological instruments,atomic absorption spectrophotometer,ultraviolet-visible spectrophotometer,micro fiber spectrometer to quantify the color parameters of Nanhong agate,and discusses color quality grading evaluation of Nanhong and Zhanguohong gate.The red color of Nanhong agate is determined by the content of Fe in the composition.Within a certain range,the higher the content of Fe,the redder the color of Nanhong agate.The strong reflection in the UV-Vis spectrum occurs at 738 nm and643 nm,which is related to Fe³⁺.The weak reflection occurs at 350-500 nm,which is related to the charge transfer of Fe²⁺to Fe³⁺.The color of Nanhong agate is mainly expressed in medium-low lightness and medium-low-saturation orange-red.The hue angle is from 16°to 85°.During the change of the dominant wavelength from 624 nm to 578 nm,the main color of Nanhong agate transitions from red to orange to orange yellow;the chroma is in the range of6.918 to 55.904,most of the degree is medium and low,and a few degree is lower;the lightness is mainly graded as 4th,and a very small number is low and high,and the two types of brightness both approach the medium brightness.According to the main color is red-orange red-orange-orange yellow,chroma is medium high-medium-middle low-low,lightness is high-medium-low,try to divide the quality of Nanhong agate color into Q-1 To Q-4 level.The red part of Zhanguohong agate is based on the grading standard of Nanhong agate.According to the main color is yellow-brownish yellow-yellowish brown,and the chroma is medium low-low and medium in brightness,the quality of Zhanguohong agate color was divided into Y-1 to Y-3 levels.The filling treatment can improve the cracks in the Nanhong agate and the smaller areas of uneven color,and improve the overall appearance.The color difference between the natural agate and the colorless epoxy resin filling treatment agate were all less than 1.5,which is in the undetectable range of human eyes,and its influence is negligible in chromaticity experiments.