Spectral Characteristics of Natural and Heated Blood-Red Ambers
XIAO Rui-hong1, WANG Li-sheng1, CHEN Wen-jun2, SHI Guang-hai2*
1. Gemmological Institute，Hebei GEO University，Shijiazhuang 050031，China
2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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 C=O 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，C=C bond and the increasing of C—O，C=O 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.
[1] Shi G H, Grimaldi D A, Harlow G E, et al. Cretaceous Research, 2012, 37: 155.
[2] SHI Guang-hai, LIU Ying-xin, YUAN Ye, et al(施光海，刘迎新，袁 野，等). Earth Science Frontiers(地学前缘), 2017, 24(6): 142.
[3] Follett Thelma. Archaeology, 1985, 38(2): 64.
[4] Stephan V, Klaus B, Pieter G, et al. Antiquity, 2012, 86(333): 660.
[5] Liu Y, Shi G H, Wang S. Gems & Gemology, 2014, 50(2): 134.
[6] Pastorelli G. Journal of Cultural Heritage, 2011, 12(2): 164.
[7] Murillo-Barroso M, Martinón-Torres M, Sanjuán L G, et al. Journal of Archaeological Science, 2015, 57: 322.
[8] Truic G I, Teodor E D, Teodor E S, et al. Journal of Archaeological Science, 2012, 39(12): 3524.
[9] Teodor E S, Teodor E D, Virgolici M, et al. Journal of Archaeological Science, 2010, 37(10): 2386.
[10] WANG Ya-mei, YANG Ming-xing, YANG Yi-ping, et al(王雅玫, 杨明星, 杨一萍, 等). Journal of Gems & Gemmology(宝石和宝石学杂志), 2010, 12(4): 25.
[11] Wang Yamei, Yang Mingxing, Yang Yiping. Gems & Gemmology，2014, 50(2): 142.
[12] WANG Ya-mei, YANG Ming-xing, NIU Pan(王雅玫, 杨明星, 牛 盼). Journal of Gems & Gemmology(宝石和宝石学杂志), 2014, 16(2): 10.
[13] XING Ying-ying, QI Li-jian, MAI Yi-cheng, et al(邢莹莹, 亓利剑, 麦义城, 等). Journal of Gems & Gemmology(宝石和宝石学杂志), 2015, 17(2): 8.
[14] WU Zong-hua, CHEN Shao-ping(吴宗华, 陈少平). Chemistry & Industry of Forest Products(林产化学与工业) , 2000, 20(3): 13.
[15] OUYANG Miao-xing, YUE Su-wei, GAO Kong(欧阳妙星, 岳素伟, 高 孔). Journal of Gems & Gemmology(宝石和宝石学杂志), 2016, 18(1): 24.
