光谱学与光谱分析, 2019, 39 (4): 1053, 网络出版: 2019-04-11   

天然血珀与烤色“血珀”的谱学特征鉴别

Spectral Characteristics of Natural and Heated Blood-Red Ambers
作者单位
1 河北地质大学, 河北 石家庄 050031
2 中国地质大学地质工程与矿产资源国家重点实验室, 北京 100083
摘要
血珀是琥珀中红色透明的品种, 因其色红如血而深受消费者喜爱。 天然血珀产量少, 价格一直较外观相似的其他颜色琥珀高。 由此, 一些本来颜色非红或者红色浓度不足者, 被人为技术变红或者更红。 现今消费市场中有许多通过一种烤色技术而成的“血珀”用来冒充天然血珀, 被用来迷惑消费者以达到追求高额利润的目的。 因此, 对天然血珀和烤色血珀的谱学特征分析并将其作为鉴定依据有重要的理论意义和实际意义。 通过对天然血珀(4件)和烤色血琥珀(9件)采用常规宝石学测试方法、 傅里叶变换红外光谱仪、 紫外-可见分光光度计等分析, 给出了二者谱学特征, 并总结和探讨了天然与烤色血珀的鉴别特征。 宝石学测试、 红外光谱测试及紫外可见光谱分析均在河北地质大学珠宝学院完成。 红外光谱测试采用NICOLET is5型傅里叶变换红外光谱仪, 紫外-可见光光谱测试运用型号为GEM-3000的紫外-可见分光光度计。 结果表明: 烤色及天然血珀在相对密度、 紫外荧光、 表面及内含物特征等方面有明显不同。 烤色血珀平均相对密度略小, 天然血珀的平均相对密度在1.075左右; 而烤色血珀平均相对密度在1.045附近。 烤色琥珀长波、 短波紫外光下均无荧光, 天然血珀在长波紫外灯下有较弱的蓝色荧光。 烤色血珀内部流体包裹体不完整, 几乎全部爆破成树枝状、 圆盘状。 烤色血珀表面广泛发育龟裂纹且裂隙中颜色更深, 并伴有红色的斑点、 流纹, 颜色呆板附在表面; 天然血珀气泡很少全部爆破, 红色分布均匀且过渡自然, 表面有风化纹。 经烤色后琥珀基本分子骨架虽未遭到严重破坏, 但烤色血珀与天然血珀在2 930, 1 724, 994和1 157 cm-1等处红外光谱吸收峰的强度与位置存在一定的差异, 如: 烤色血珀在2 930 cm-1处指示C—H饱和不对称伸缩振动的吸收峰的峰强度与天然血珀相比明显较弱; 烤色琥珀在1 724 cm-1指示CO波段的峰的峰强度较天然琥珀明显增强, 而且吸收峰的峰位较天然血珀吸收峰位偏大; 1 029与975 cm-1处的峰指示酯中C—O伸缩振动, 烤色琥珀的两峰在此趋于合并呈现单峰且吸收峰宽而强, 而天然血珀在此两处的吸收峰窄而弱; 并且, 相比于天然血珀, 烤色血珀的975 cm-1峰明显向大波数处移动至997 cm-1附近。 天然血珀有1 158和1 227 cm-1次强峰及1 180 cm-1附近的弱吸收峰; 烤色琥珀此处的吸收峰趋于单峰化, 吸收峰位置在1 160 cm-1附近, 吸收峰的强度较天然血珀明显增加。 天然血珀在1 457 cm-1处和1 376 cm-1处两处吸收峰的强度远远大于烤色血珀, 且天然血珀峰的最高点从1 457到1 376 cm-1呈下倾趋势, 烤色血珀呈水平与水平向上趋势。 烤色血珀在975~1 029 cm-1处的峰合并成宽的单峰。 在紫外可见光谱中, 天然血珀在660 nm处转折幅度明显大于烤色血珀。 以上特征可以考虑作为鉴别天然与烤色血珀的关键证据。 烤色与天然琥珀的谱学特征差异, 推测主要是因为含C—H, CC键的耗减, C—O, CO键等含氧结构的增加所致。
Abstract
Blood-red amber is the kind of amber with red coloration, which is so popular in jewelry market. Natural blood-red amber is rare and expensive. Anyway, there is so much heat-treated blood-red amber emerges to make consumers confused. So it is an urgent task to distinguish heat-treated amber from the natural one. In this work, natural and heated blood-red amber samples were tested by conventional gemmological methods, infrared spectrometer and UV-Vis spectrophotometer, including 4 natural blood-red amber samples and 9 heat-treated blood-red amber samples. The blood-red amber samples were all tested in Hebei GEO University. The NICOLET is5 Fourier transform infrared spectrometer was used to do the infrared spectrum test. And the UV- visible spectrum was tested by GEM-3000 UV- visible spectrophotometer. The results indicated: The average relative density of the heated blood-red ambers was slightly smaller, for the average relative density of the natural blood-red amber samples was around 1.075 compared to 1.045 for the heated ones. The heated blood-red amber samples have no fluorescence under long wave and short wave ultraviolet light, while the natural ones appear weak blue fluorescence under the long wave ultraviolet lamp. The internal fluid inclusions of heated blood-red amber samples are broken and almost all burst into tree branch shape and disc shape. The surfaces of the heated blood-red ambers are widely developed in turtle cracks, and the red color, with red spots and streaks, is darker in the fissure than anywhere else. And the colorations are attached to the surface of heated blood-red amber samples. The internal fluid inclusions of the natural blood-red ambers are rarely burst. The red color distribution on natural blood-red ambers is uniform and natural, with little cracks for being weathered. Heated and natural ambers have obvious differences in relative density, UV fluorescence and inclusions, etc. The basic molecular skeletons of blood-red amber samples have not been seriously damaged after heated. The differences between heated and natural ambers lie on the aspects of intensities and locations of infrared absorption peaks at 2 930, 1 724, 994, 1 157 cm-1. The peaks at 2 930 cm-1 in heated blood-red amber samples, which is implication of saturated C—H asymmetric stretching vibration, are less intense than that in natural blood-red amber samples. There is enhancement in the intensity of peaks at 1 724 cm-1, indicating CO bond, for heated blood-red ambers comparing the natural ones with a larger locations. Peaks at 1 029 and 975 cm-1 are signals for C—O stretching vibrations in infrared spectrum. The peaks of heated blood-red ambers trend to merging to a single one peak at these two points with broad width and high intensity, while the peaks of the natural ones appear thin and short. The peaks at 975 cm-1 of the heated blood-red ambers shift to around 997 cm-1 obviously. Peaks at 1 158, 1 227 and 1 180 cm-1 of natural blood-red ambers can be found, while there are single peaks with no shoulder peaks at 1 160 cm-1 of heated blood-red ambers. From 1 457 to 1 376 cm-1 the absorption peak intensities of natural amber samples are much higher than those of heated ones. And the natural blood-red amber samples showed downward trends in IR-spectrum, while heated amber showed a horizontal or horizontal upward trends. The absorption peaks of heat-treated amber samples from 975 to 1 029 cm-1 merge into wide single peaks, which is the key evidence to identify natural and heated blood-red ambers. The difference of the infrared absorption peaks between heated and natural ambers is speculated to be mainly caused by the breaking of C—H, CC bond and the increasing of C—O, CO and other oxygen bond structure. UV-Vis spectra of blood-red amber samples revealed: in the turning region of 660 nm, the turning areas of natural blood-red amber samples are greater than the heated amber samples.

肖瑞红, 王礼胜, 陈文君, 施光海. 天然血珀与烤色“血珀”的谱学特征鉴别[J]. 光谱学与光谱分析, 2019, 39(4): 1053. XIAO Rui-hong, WANG Li-sheng, CHEN Wen-jun, SHI Guang-hai. Spectral Characteristics of Natural and Heated Blood-Red Ambers[J]. Spectroscopy and Spectral Analysis, 2019, 39(4): 1053.

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