Spectroscopic Identification of Amber Imitations: Different Pressure and Temperature Treatments of Copal Resins

Copal resins can be treated with heat and/or pressure to imitate ambers in the gem market. To explore the effects of different modification conditions on post-treatment spectral changes, five experimental methods with different temperature–pressure parameters were designed to modify two types of copal resins. The treated copal resins were examined by infrared, Raman and nuclear magnetic resonance spectroscopy. Results indicate that all the treatment methods simulate the maturation process, with spectral characteristics becoming more similar to those of ambers. Multi-stage heat–pressure treatment has the most significant effect on Colombia and Madagascar copal resins, with their spectra being similar to those of Dominican and Mexican ambers. Rapid high-temperature treatment at 180 °C modified the Borneo copal resin, with its infrared spectrum developing a “Baltic shoulder” resembling that of heat-treated Baltic amber. Even though there are many similarities between treated copal resins and natural ambers, they can still be distinguished by spectroscopic methods.