A Review for the Gemmological Research on Amber

Amber, an organic gemstone also named fossil resin, gradually matured from the liquid resin secreted by paleobotanical trees in different geological ages. During the long fossilization process, the internal components and chemical structures in the initial liquid resin were maturated into these of fossil resins, which integratedly controlled by many external factors, like paleoclimate, paleogography conditions, mother-trees, and depositional environment. These inconstant factors lead to that amber from different producing areas enormously varies in the gemmological characteristics, spectral features, chemical components, micro-structures, quality evaluation indices, and market values. Thus, it is of great scientific significance and application value to study amber deeply, systematically, and in detail. Based on the research approach of from the surface to the inside, from the simple to complex, the authors and the research team established a comprehensive database for amber. This database includes the mid-infrared spectra collected by KBr pellets pressing method, the excited-emission matrix by JASCO FP8500 fluorescence spectrometer, the time-resolved phosphorescent spectra and the decay times by Edinburgh FLS980 spectrometer, as well as the stable isotope tracing technology. Current application of this database is used in the geographic identification of amber and ancient amber artworks. Meanwhile, the luminescence behaviors (fluorescence and phosphorescence), as the important gemmological properties of amber, have been deeply studied, and the potential fluorescent components have been analyzed. A quantification of the total luminescence behaviors' parameters in amber laid the foundation to propose blue amber quality evaluation indices and rules. On the other hand, the amber enhancement and treatment technologies are developing rapidly to meet the market kinds of new demands. Focus on characterizing the gemmological and spectral features of various new-type man-made amber products in market, a series of identifying methods are proposed and keep updating with the market demands refresh. Additionally, amber as a natural macromolecular polymer, because of its complex multi-components, it has become one kind of significant objects in various interdisciplinary studies. Amber contains lots of volatile and non-volatile components, varying with its producing areas. Due to its slightly solubility in normal organic solvent, the compounds dominant in amber are extremely hard to isolate and purify. The biomarker named 15-nor-cleroda-3, 12-diene was firstly identified from a Dominican amber sample, by gas chromatography-mass spectrometer (GC-MS) detection for the saturated hydrocarbon, aromatic hydrocarbon, non-hydrocarbon fractions composition and insoluble polymers. Then combined with the high resolution mass spectrometer and nuclear magnetic resonance (NMR) technology, its planar and stereoscopic structures were determined. This proposal indicates that Dominican amber is not only based on polymerized labdanoid diterpenes, but also on 15-nor-cleroda-3, 12-diene which has typical the cleroda-diene skeleton structure. Amber as a precious cultural relic, current scientific and technological archaeology provides a new sight to trace the amber relics ancient producing areas, and further reveals the ancient communication between East and West cultures.