Spectroscopic Characteristics of Amber, Copal Resin and the Improved Derivatives

In recent years, amber identification has still been a hot topic in academic research field. Amber, copal resin, pressed amber and heated copal resin are investigated using three non-destructive testing methods, including the conventional gemological testing method, Fourier transform infrared spectrum and Raman spectrum as a supplementary. From FT-IR testing results, amber, copal resin, pressed amber and heated copal resin have the similar basic FT-IR characteristics, such as absorption bands at 2 980—2 900 cm⁻¹ and 2 900—2 800 cm⁻¹ caused by the saturated C−H bond stretching vibration and the corresponding infrared absorption bands at 1 480—1 430 cm⁻¹ and 1 400—1 350 cm⁻¹ caused by CH₂−CH₃ bending vibration. Compared with amber, FT-IR characteristics of copal resin show infrared absorption at 889 cm⁻¹, and FT-IR characteristics of pressed amber show strong absorption at 1 723 cm⁻¹. When copal resin is heated, the absorption at 1 645 cm⁻¹ is disappeared. Amber, copal resin, pressed amber and heated copal resin only have slight differences in the Raman shift. Compared with amber, copal resin lacks in the Raman shift at 1 720 cm⁻¹. Through the exploration of its basic characteristics and analysis of the attribution of its functional group characteristic peaks, the differences and connections can be found among amber, copal resin, pressed amber and heated copal resin. The results show that the Gem identification should be combined with its physical and chemical properties and spectral characteristics.