Study on Freshwater Cultured White Pearls From Anhui Province Based on Chromaticity and Raman Spectra
LI Meng-meng1, TENG Ya-jun2, TAN Hong-lin1, ZU En-dong1*
1. Faculty of Materials Science and Engineering, Kunming University of Science and Technology，Kunming 650093, China
2. Kunming Customs Technology Center, Kunming 650228, China
Abstract：The color of the pearl is one of the most critical factors affecting its quality. At present, most researches on pearl’s color focus on the constituent elements, coloring mechanism and structural differences of different colors, but there are few studies on how to distinguish the pearl of the same color intuitively. In this paper, three batches of freshwater cultured white pearls from different periods in Anhui were selected and subjected to colorimetry, laser Raman spectroscopy and gemstone microscope observation. Based on this, the relationship between the whiteness value and Raman spectrum of white freshwater cultured pearls was established. Then combined with the observation of gemstone microscope, it provides the basis for the division of its color grade.This paper uses the Hunter whiteness formula, WHT=100-[(100-L*)2+a*2+b*2]1/2 to calculate the whiteness value of different pearls, and then compares the whiteness value with the R value, which is the ratio of the peak area of the 1 132 cm-1 caused by the C—C stretching vibration and the aragonite peak area caused by the symmetrical stretching vibration of the[CO3]2-. It is found that the whiteness value of the freshwater cultured white pearl is inversely proportional to the R value of Raman spectra. The cluster analysis in SPSS can be used to classify the colors of freshwater cultured white pearls from Anhui. By cluster analysis, the whiteness values can be divided into four ranges: above 85, 85~80, 80~75 and below 75. The whiteness value above 85 are the whitest, 85~80 are white, 80~75 are medium whiteness, 75 or less are the worst. By observing the surface morphology of Anhui freshwater cultured white pearls, it can be found that pearls with a whiteness value above 85 have a smoother surface and strong gloss. Pearls with a whiteness value between 85 and 80 have some defects, and strong gloss on the surface, pearls with a whiteness value between 80 and 75 have obvious defects and medium gloss, pearls with a whiteness value below 75 have more defects and poor gloss on the surface. The smoothness and gloss of pearls will affect the whiteness. Both the whiteness value and the R value of the Raman spectra can quantitatively indicate the whiteness of Anhui freshwater cultured white pearls. The relationship between them is that the larger the whiteness values are, the smaller R values in Raman spectrum are, and the whiter pearls are. The gloss and smoothness of pearls can be used as an auxiliary basis for judging the whiteness of pearls. The whiteness of freshwater cultured white pearls can be distinguished by coloration parameters, Raman spectra and microstructure observation. They can also provide a theoretical basis for the classification of the color grade of freshwater cultured white pearls.
Key words：Anhui; Freshwater cultured; White pearls; Raman spectra; Chromaticity
李萌萌，滕亚君，谭红琳，祖恩东. 基于色度学与拉曼光谱的安徽淡水养殖白色珍珠研究[J]. 光谱学与光谱分析, 2022, 42(05): 1504-1507.
LI Meng-meng, TENG Ya-jun, TAN Hong-lin, ZU En-dong. Study on Freshwater Cultured White Pearls From Anhui Province Based on Chromaticity and Raman Spectra. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(05): 1504-1507.
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