各类金色海水珍珠的呈色属性及UV-NIS反射光谱
Colouration Attributes and UV-NIS Reflection Spectra of Various Golden Seawater Cultured Pearls
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摘要: 针对各类金色海水珍珠的呈色属性、改色处理及其鉴定问题,采用LA-ICP-MS、拉曼光谱仪、UV-NIS微光谱仪等测试仪器,重点对近期市面上出现的金色海水珍珠与染色处理金色海水珍珠样品的化学成分、拉曼光谱、反射光谱、呈色属性及表面微观特征进行了测试与研究。结果表明,金色海水珍珠样品的化学成分与UV-NIS反射光谱特征在很大程度上依附并继承了金唇贝的基本属性,以356 nm(±2 nm)为中心的吸收谱带可作为识别金色海水珍珠是否染色的诊断性证据之一;颜色欠佳的海水珍珠通常采用人工有机色素予以染金色,经染色处理后的金色海水珍珠样品显示与金色海水珍珠截然不同的呈色属性和UV-NIS吸收谱带。浅表层染色处理金色海水珍珠样品通常在其珍珠表层形成厚约15μm(通常<20μm)、着色相对均匀的金黄色渗色层,其在紫外-可见光范围内呈现2组特征的吸收谱带:一组位于可见光蓝紫区427 nm(±2 nm)处,归因人工染色剂所致;另一组则位于紫外区353 nm(±2 nm)处,为自身的有机致色因子所致;深层染色处理金色海水珍珠样品沿其珍珠表层向内层形成厚约50~80μm、着色均匀的金黄色渗色层,由人工染色剂致特征吸收谱带主要位于可见光蓝紫区426 nm(±2 nm)处,具有重要的鉴定意义。金唇贝样品中的金黄色珍珠内层的特征吸收谱带与金色海水珍珠样品的基本雷同,其356 nm(±2 nm)处特征吸收谱带的相对强度与其珍珠层内黄色有机色素的浓度呈正相关关系。对金色海水珍珠的呈色属性及其与金唇贝之间的耦合关系予以了探讨。Abstract: In view of the colouration attributes,colour alteration and the identification,the chemical compositions,Raman spectra,reflection spectra,colouration attributes and the surface micro-characteristics of the undyed and dyed golden seawater cultured pearl samples on the recent market are investigated by using the LA-ICP-MS,Raman spectrometer,UV-NIS micro spectrometer and the other testing instruments.The results show that the chemical compositions and the features of the UV-NIS reflection spectra of the golden seawater cultured pearl samples adhere and inherit the basic attributes of the golden-lip shellfish to a large extent.The UV-NIS absorption band centred at 356 nm(±2 nm) can be used as one of the diagnostic evidences in separating undyed from dyed golden seawater cultured pearls.The organic dye used for enhancing colour of the dyed pearl samples show the distinctively different absorption bands from that of the undyed ones.The surfaces of the superficial layer dyed golden seawater cultured pearl samples are of an evenly coloured golden penetration whose thickness is about 15 μm(normally<20 μm).Under the range of the UV visible light,there are two major groups of absorption bands.One is at 427 nm(±2 nm) related to the artificial dying agent,and another is at 353 nm(±2 nm) which belongs to the organic colourants originally present in the pearls.On the other hand,the outer layer of the deep-layer dyed golden seawater cultured pearl samples are of an evenly coloured golden penetration whose thickness is about 50~80 μm with only one diagnostic absorption band at 426 nm(±2 nm) caused by the artificial colouring agent.The features of the absorption bands of the golden inner nacre of the golden-lip shellfish samples are basically the same as that of the undyed golden seawater cultured pearl samples.The relative intensity of the absorption band at 356 nm(±2 nm)is positively correlated to the concentration of the yellow organic pigments present in the nacre.In this paper,the relationship between the colour attributes of the golden seawater cultured pearl samples and the golden-lip shellfish samples is discussed.
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