Study on Color Formation and Identification Characteristics of Blood Amber Produced by Irradiation
SUN Kai-yue1, 2, CHEN Xiao-ming2, HAN Wen2*, HE Ming-yue1*, LU Tai-jin2
1. School of Gemmology, China University of Geosciences, Beijing, Beijing 100083, China
2. National Gems & Jewelry Testing Co. Ltd., Beijing 100013, China
Abstract：Amber is a kind of organic gemstone with high value, and blood amber is a new kind of amber appearing in recent years, which is generally believed to be artificially irradiated. Four pieces of natural amber and one piece of copal resin were selected to be irradiated by an electron beam combined with a 60Co radiation source to change their color. It indicates that the irradiated samples showed the appearance characteristics of blood amber, and the color is bright red. Magnification observation was used by a 3D microscope system. UV-Vis, FTIR, and electron paramagnetic resonance were used to systematically study the samples before and after color modification. It can draw the following conclusions. After irradiation, the dendritic lightning striations were formed in amber and copal resins, which is the lightning streak discharge channel produced by insulator material under electron beam bombardment. Because there are pits, cracks and other positions in amber and copal resins, it often becomes the trigger point of breakdown and discharge. Therefore, the discharge trace will be left when the solid medium is broken down. There is no difference in the dendritic lightning striations between amber and copal resins after irradiation, and they are distributed in a single branch.IR and UV-Vis spectra have no significance in identifying whether amber and copal resin have been irradiated. It is no difference in the characteristic absorption peaks of the samples before and after color modification, indicating that the molecular skeleton was not seriously damaged. Electron paramagnetic resonance (EPR) spectra reveal that the irradiated amber andcopal resins will lead to the splitting of covalent bonds of some hydrocarbon groups in their structure and the formation of atomic groups with unpaired electrons, which is the free radical. The longer the irradiation time, the larger the formant area, indicating the higher the spin concentration of free radicals and the more obvious the color deepened. The formant area of all samples before irradiation is almost zero, indicating the spin concentration of free radicals in natural amber and copal resin is close to zero. It can be inferred thatthe generation of free radicals is the fundamental cause of color change. Electron paramagnetic resonance testing can determine the relationship between the spin concentration of free radicals produced by irradiation and color by scraping the small amount of power. Combined with the generation of the dendritic lightning striations, it can be used as the distinguishing characteristic of blood amber produced by irradiation.
Key words：Amber; Copalresin; Irradiation; Free radical; Electron paramagnetic resonance
孙凯悦，陈晓明，韩 文，何明跃，陆太进. 辐照处理血蜜蜡的颜色成因及鉴定特征研究[J]. 光谱学与光谱分析, 2023, 43(05): 1459-1464.
SUN Kai-yue, CHEN Xiao-ming, HAN Wen, HE Ming-yue, LU Tai-jin. Study on Color Formation and Identification Characteristics of Blood Amber Produced by Irradiation. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2023, 43(05): 1459-1464.
