Coloring Factors of Natural and Dyed Golden Pearls and Research Progress on Their Identification Methods
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摘要:
金属离子、卟啉和类胡萝卜素是天然金珍珠的主要致色成分, 有机染料是染色金珍珠的致色成分。鉴定天然金珍珠和染色金珍珠的主要手段有常规观察检测、紫外可见吸收光谱法、拉曼光谱法、荧光光谱等。本文结合天然金珍珠的致色成分和染色金珍珠的染色方法, 对两类金珍珠的鉴定技术作了评述, 认为常规观察检测是十分必要的, 染色珍珠颜色分布不均匀, 在孔眼内或表面破损处可看到染料的沉淀浓集; 紫外可见吸收光谱法是目前较为常用的鉴定方法, 天然金珍珠主要吸收峰位于350~360 nm, 而染色金珍珠则出现明显的410~450 nm谱峰; 应用拉曼光谱法鉴定可获得天然金珍珠在275 cm-1明显的特征峰, 而染色金珍珠出现强的荧光背景峰; 应用荧光光谱法鉴定金黄色天然珍珠在376 nm处光激发时谱峰是以472 nm为中心, 而染色珍珠在372 nm处受光激发时谱峰位于436 nm。这些鉴定方法仍然在实验验证阶段, 进一步优化和开发新的测试手段则是今后重要的发展方向。
Abstract:Color-causing components of natural golden pearls are mainly metal ions, porphyrin and carotenoids. Organic dyes are the color-causing components of dyed pearls. Conventional observation, UV-vis Absorption Spectroscopy, Raman Spectroscopy, and Fluorescence Spectroscopy are used to distinguish natural from dyed pearls. The identification methods of the two types of pearls (natural golden and artificially dyed golden) are reviewed and presented in this study. Conventional observation is necessary because the color of dyed pearls is not homogenous and dye can be concentrated in the hole or any damaged surface. UV-vis Absorption Spectroscopy is a commonly used identification method. The main absorption peaks of natural golden pearls lie between 350 nm and 360 nm, whereas those of dyed pearls lie between 410 nm and 450 nm. Raman Spectroscopy has identified that natural golden pearl has a characteristic peak of 275 cm-1, but dyed pearl has a strong fluorescence background peak. Fluorescence Spectroscopy has identified that the natural golden pearl has a central peak of 472 nm as excitation by 376 nm light, whereas the dyed pearl has a central peak of 436 nm as excitation by 372 nm light. Further verification of these identification methods should be undertaken, along with improvements in optimization and the development of new methods.
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表 2 胡萝卜素在可见光区的吸收峰
Table 2. Absorption peaks of renieratene in the visible region
种类 最大峰位λmax(nm) α-胡萝卜素 422 444 473 β-胡萝卜素 425 449 476 ε-胡萝卜素 416 440 470 
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