Choudhary G. (2014) Emeralds Partially Coated with Amorphous Carbon. The Journal of Gemmology, Vol. 34, No. 3, pp 242-246
Nine faceted emeralds submitted to the Gem Testing Laboratory, Jaipur, India, were identified as coated owing to the metallic to sub-metallic reflections on their pavilion facets. The coated surfaces did not show any diagnostic features with routine EDXRF and Raman spectroscopy. However, some samples had concentrations of the coating substance in surface cavities, and Raman analysis of those areas revealed the presence of amorphous carbon. Specifically, the presence of a broad absorption feature at ~1550 cm-1 with a shoulder at ~1360 cm-1 identified the coating substance as an ‘a-C’ type film. Microscopic observation showed that the coating was damaged and removed from several areas, suggesting its instability to normal wear and tear.
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