紫外-可见光谱仪在区分天然颜色和染色金珍珠的局限性

Limitation on Ultraviolet-Visible Spectrometer to Distinguish Golden Pearl and Dyed Golden Pearl

  • 摘要: 随着金珍珠饰品的流行,市场上出现越来越多的颜色处理过的金珍珠。天然颜色的金珍珠与染色金珍珠的价格相差甚远,故金珍珠的颜色检测显得尤为重要。目前,紫外-可见光谱仪(UV-Vis)被认为是有效鉴别金珍珠颜色的测试手段之一,但在检测工作中,当利用紫外-可见光谱仪判定某些金珍珠是否染色时,发现其结论存在一定的争议性。前人的研究显示,在紫外-可见光谱中出现350~360nm处的吸收峰为天然色素的吸收所致,410~450nm出现明显吸收峰归因于有机染料所致。在实际工作中,笔者发现一些金珍珠样品不同部位的紫外-可见光谱不一样,有时测试结果还与显微镜下的特征相矛盾。因此,笔者初步分析了金珍珠的颜色成因,探讨了紫外-可见光谱仪在检测金珍珠时存在的局限性。

     

    Abstract: With the popular of golden pearl ornaments,more and more dyed golden pearls appear on the market.Since the price of natural colour golden pearls and dyed golden pearls is extremely different,the colour detection is quite important.Gemmologists and detection experts try to analyze the differences between golden pearls and dyed golden pearls with the help of Raman spectrometer,ultraviolet-visible spectrometer(UV-Vis),laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS),fluorescence spectrometer and cathodo luminescence(CL).UV-Vis spectrometer is considered to be one of the effective ways to identify the colour of golden pearls,but this method is not mature and has some controversial opinions with testing results because of the relatively short time development.The previous studies considered that the UV-Vis spectrum peaks between 350~360nm were caused by natural pigment of golden pearls and obvious peaks between 410~450nm were caused by the organic dye of dyed golden pearls.However,in practical work,the testing results of UV-Vis spectrometer are quite different in different parts of golden pearls.Sometimes it shows conflicting results between microscope observation and UV-Vis spectra,since some golden pearls being natural colour also have absorption peaks at 400nm.Limitation of UV-Vis spectrometer on studying the cause of golden colour of the pearls is discussed and it is concluded that UV-Vis spectrum absorption peaks at 400nm are related to the structure of pearl layer.

     

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