Application of pyrolysis-gas chromatography and pyrolysis-gas chromatography/mass spectrometry to the unmasking of amber forgeries

Attempts to forge amber inclusions have been known from ancient times, when natural materials such as melted amber or copal were used. At the very beginning of the Twentieth Century these natural materials were mostly replaced by Bakelite and similar synthetic polymers. These materials are not transparent and so can readily imitate certain kinds of milky amber but are useless in terms of transparent ambers with inclusions. In the 1940s two new classes of organic materials became available for amber imitation, i.e. polyester resins and epoxy resins. Both are transparent, able to dissolve organic dyes and can achieve an appropriate degree of hardness, depending on the addition of fillers (e.g. fiberglass), the structure of the original monomers, and the degree of crosslinking. With easy commercial availability and sophisticated “artwork” one can prepare convincing imitations of large transparent amber pieces with a wide variety of “inclusion” (ants, bees, lizards, mosquitos, etc.). Py-GC provides a simple test for the unmasking of such fakes, and Py-GC/MS can identify quite precisely the structures of the materials used for these purposes. A growing number of fossil forgeries produced in the Dominican Republic, and sold there and in New York, have been documented. The results reported are based largely on forgeries acquired by D. Grimaldi specifically for this study and kept at the American Museum of Natural History in New York; and from the Conservation Center's collection of forged artifacts and jewelry made available by New York galleries and private collectors.