The Types of UV-Vis Diffuse Reflectance Spectra of Common Gray Pearls and Their Coloring Mechanism
FANG Shi-bin1, JIANG Yang-ming1, YAN Jun1, 2, YAN Xue-jun1, ZHOU Yang3, ZHANG Jian2*
1. Zhejiang Fangyuan Test Group Co., Ltd., Hangzhou 310013, China
2. College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China
3. College of Information and Electronic Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China
Abstract：The spectral types of usual gray pearls were classified based on UV-Vis diffuse reflection spectra. The coloring mechanism of gray pearl was further investigated. The results show that :(1) based on the presence or absence of absorption peak nearby 280 nm in the reflectance spectra of gray pearls, which are firstly divided into typeⅠ (obvious absorption) andⅡ (no absorption or weak absorption). Furthermore, according to the shape of spectra and the position of the main wavelength of the reflection peak, the type Ⅰ pearls are further divided into three subtypes: Ⅰn, Ⅰp andⅠf. Among them, the color of the nucleus of typeⅠp pearl is white, and a brown or blackish-brown transition layer exists between the nucleus and nacre, which may be the direct cause of the gray color of the pearl. Meanwhile, the type ofⅠp pearls are generally considered to be untreated in the field of gemstone identification. (2) because of the change in the color of nacre before and after irradiation and the variation characteristics of the UV-Vis reflection spectrum in this work and the previous work on irradiated pearls, it is preliminarily concluded that irradiation is still one of the main reasons for the coloring mechanism of gray pearls. Moreover, the pearl can be identified as having been treated based on the disappearance of the absorption peak or the presence of only one absorption shoulder near 280 nm in the corresponding reflectance spectrum. According to the typeⅡ gray pearls section structure, the nucleated and non-nucleated pearls coexist in the circulation field. A more accurate method used to identify the irradiated pearl should be developed.
方诗彬，蒋扬名，严 俊，严雪俊，周 扬，张 俭. 常见灰色珍珠的紫外可见漫反射光谱类型及其灰色成因[J]. 光谱学与光谱分析, 2022, 42(12): 3703-3708.
FANG Shi-bin, JIANG Yang-ming, YAN Jun, YAN Xue-jun, ZHOU Yang, ZHANG Jian. The Types of UV-Vis Diffuse Reflectance Spectra of Common Gray Pearls and Their Coloring Mechanism. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(12): 3703-3708.
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