This month Anu Manchanda explains the expertise required to check for common treatments in tanzanite and rubies. Anu Manchanda picks up the tanzanite in her tweezers and holds it under her diamond light. At first sight a non-gemmologist would think it a good quality stone – a deep indigo blue with strong colour intensity; but to Anu’s experienced eye as a gemmologist it just does not look quite right. Anu moves it slowly under the light, examining it carefully with her 10x loupe. The colour looks unnaturally patchy, particularly when viewed from the crown, and a flash of iridescence as she tilts it under the reflected light makes her put down her loupe and turn to the microscope. Positioning the stone carefully, Anu examines it under higher magnification, looking closely at the facet edges and culet of the stone. She can see tiny signs of abrasion around the edges, and then, looking at the facets more closely, she finds tell-tale imperfections which confirm her suspicions: the tanzanite has been cobalt treated to improve its appearance. Anu already knows that if the stone is put under ED X-ray fluorescence it will...CONTINUE READING To read more about COBALT COATED TANZINITES  make sure to visit our meet the experts page on The Birmingham Assay Office website – To read more about WORKING WITH PALLADIUM and to find out how Palladium faired in 2012 make sure to visit our meet the experts page on The Birmingham Assay Office website – http://www.theassayoffice.co.uk/meet_the_experts/cobalt-coated-tanzanite_acexpert.html

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