New Hot Pressing Treatment of Amber and Its Identification Characteristic

In recent years, the competition of amber market is increasingly fierce, and a new amber processing technology has emerged in the market in order to reduce the processing cost and the loss of rough amber materials. After a simple and irregular cutting of the rough Baltic amber materials with the same weight as the beads, different diameter bead molds are used to heat and apply pressure to produce the beads in mass production, and the technology reduces the process and cost of traditional beads because of its one cycle formation. The amber varieties treated by this new technology can be subdivided into translucent golden twisted beeswax amber, beeswax amber, white beeswax amber, and white flora pattern beeswax amber with original skin, with particle sizes ranging from 12-20 mm or above, and commonly above 15 mm. Its appearance is extremely similar to that of natural amber, which is difficult to identify and undermine the orderly and healthy development of the amber market. In order to understand and identify this new method and products, this research reveals the identification characteristics of this new type of hot-pressed amber by means of gemstone polarizing microscope, infrared spectroscopy and photoluminescence spectroscopy.The results show that: (1) Some hot-pressed amber beads will slowly release internal pressure and rebound and deform after being placed under natural conditions for 3-6 months, with a non-circular appearance and shallow or deep turtle cracks on the surface. Besides, the stability of the beads treated by this hot pressing is poor. If heated at 100 ℃ for 8-10 minutes, the amber beads will exhibit their irregular morphology before hot pressing treatment.(2) When turning the hot-pressed translucent golden amber and beeswax amber beads, part of the surface show a silk-like luster that is different from the amber/resin luster, which is speculated to be caused by the micro flow lines generated by directional pressure. Through the extinction phenomenon under the polarizing microscope, the original engraved edges and occlusal marks caused by mold can be observed in amber with higher transparency. (3) There are slight differences in the infrared spectra of hot-pressed amber comparing to that of natural amber, indicating the infrared spectral characteristics of heat treated amber, especially the absorption peak of 888 cm^-1 caused by the out of plane bending vibration of C-H on the C=C double bond, which mostly disappears or weakens. The photoluminescence peak positions of photoluminescence spectrum are basically consistent, but under the same test conditions, the luminescence intensity is weakened, and the identification is of little significance.