The Gemological Institute of America (GIA) has examined a rare pink diamond displaying an unusual mottled appearance, shedding light on how a combination of advanced treatments can influence both colour and visual texture.

The 1.10-carat round diamond, submitted to GIA’s New York laboratory, was graded as fancy deep brownish orangey pink. According to findings published in the fall issue of GIA’s Gems & Gemology journal, the stone stood out due to its patchy, mottled look—an uncommon feature in treated pink diamonds.

GIA’s analysis revealed that the diamond had undergone multiple enhancement processes, including High Pressure-High Temperature (HPHT) annealing, laboratory irradiation, and subsequent moderate heating. These treatments worked together to create nitrogen-vacancy (NV) centres within the stone, which are responsible for producing the pink colour. Prior to treatment, the diamond was originally brown.

Microscopic examination showed that the mottled pattern extended from shallow depths all the way to the polished surface. Further testing using visible and near-infrared (Vis-NIR) spectroscopy identified features consistent with irradiation and heat treatment.

GIA noted that the distinctive mottled appearance likely resulted from an uneven distribution of NV centres, influenced by the diamond’s nitrogen aggregates. While detailed mapping was not conducted to confirm this theory, the findings provide valuable insight into how complex treatment pathways can create unexpected visual effects in coloured diamonds.