Twins separated at birth: Identifying pairs of polished diamonds with irradiation-related color from the same rough by fingerprinting using imaging and spectroscopy

Some of the most famous diamonds of historical significance display beautiful and rare colors such as pink, blue and green. Many have been recut one or more times, either in attempts to improve their appearances, or to disguise their provenance. Given the major advances in instrumentation for characterizing diamonds in the past two decades, we pose the question: can one devise a methodology to create an analytical fingerprint of a diamond to identify it even after recutting, or to identify two polished diamonds of unknown provenance as having been cut from the same rough or polished diamond? To determine if this is feasible, we carried out an in-depth study of two pairs of polished diamonds colored mainly by the GR1 absorption, one pair known to have been cut from the same rough crystal, and one pair of diamonds of unknown provenance for which it was possible to prove that they originated from the same piece of rough. The data obtained by a combination of absorption spectroscopy from the UV to the mid-infrared, photoluminescence spectroscopy with various lasers from the UV to the NIR and luminescence imaging with a range of excitations was found to establish, beyond any doubt, that each of the two diamond pairs shared a common progenitor.Nevertheless, for each of the diamond pairs only one diamond was identified as naturally colored while for the other one the color origin was given as “undetermined” by a prominent gem testing laboratory. The methodologies described herein can prevent such inconsistencies regarding diamonds of previously unknown provenance; they show spectroscopically how and why the color of some natural color origin green diamonds is enhanced by polishing, especially when removing surface radiation “stains”; further, such methodologies will identify “diamond twins separated at birth”.