A selection of natural green diamond, rough and faceted. Note: These diamonds are not among those recalled by the Gemological Institute of America. Image credit: GIA GIA recalls fancy colour diamonds over undetected treatment Posted April 26, 2021 | By Arabella Roden • Editor The Gemological Institute of America (GIA) has withdrawn the grading reports for a number of diamonds and requested the stones be sent back for re-testing, over concerns an as-yet unidentified treatment could have gone undetected.
The diamonds in question were assessed between January and June 2020 and issued with a “green or greenish” colour grade, with a spokesperson for the GIA telling Rapaport News, “Recent research and investigation into potential treatment methods caused us to request the return of the subject diamonds for further analysis.”
"We recently discovered new information that may provide new insights about the origin of colour of the group of diamonds that we have requested to be returned for review"Gemological Institute of America spokesperson
The spokesperson added, “GIA has been investigating the cause of colour in diamonds and other gem materials for nearly 70 years. Among GIA’s earliest areas of research was determining origin of colour of green diamonds, which remains even today one of the most difficult areas of gemmology.
“The research process is dynamic, and we recently discovered new information that may provide new insights about the origin of colour of the group of diamonds that we have requested to be returned for review.”
The exact number of diamonds recalled was not disclosed. The GIA has reportedly removed the diamonds from its Report Check service and the re-testing was offered free of charge.
Rapaport News quoted unnamed sources as saying “many” of the stones had already been re-tested, with their natural-colour status confirmed; diamonds graded as ‘Undetermined’ by the GIA can be difficult to sell – more so than ones graded as ‘Treated’.
Natural green diamonds are formed by exposure to radiation, which displaces carbon atoms in the stone’s crystal lattice.
The most common treatment to induce green colour involves exposing yellow or near-colourless diamonds to radiation from a low-energy electron beam.
Artificial irradiation usually results in “shallow colour zoning that penetrates into the stone and aligns with the facet shape,” according to the GIA, which makes it easy to detect; the nature of the suspected new treatment has not been specified.