Simultaneous X-Radiography, Phase-Contrast and Darkfield Imaging to Separate Natural from Cultured Pearls
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Krzemnicki, M. S.
Hanser, C. S.
The separation of natural from cultured pearls is mainly based on the interpretation of their internal structures, which traditionally have been visualized by X-radiography and more recently by X-ray computed microtomography (micro CT). In this study, the authors present a new analytical approach using a grating interferometer, which simultaneously generates an X-radiograph, a phase-contrast image and a small-scale scattering or darkfield image. The latter two additional images provided by this technique offer detailed and complementary information, as they are especially sensitive for visualizing tiny material inhomogeneities in pearls such as fissures, organic layers and cavity structures. Using seven selected natural and cultured pearl samples and a strand of non-beaded freshwater cultured pearls, the authors demonstrate that this new analytical approach offers versatile and rapid pearl identification possibilities, especially as it is possible to analyse not only single loose pearls but also entire strands and necklaces. Compared to micro-focus digital radiography and micro-CT, certain limitations in resolution still remain with the described prototype setups, and as such this new methodology should be considered a helpful complementary technique to the classical radiography of pearls.
Journal of Gemmology, vol. 35 (7), pp. 628-638, 2017.