GIA Examines Color-Treated Purple Diamond

The Gemological Institute of America (GIA) recently studied a purple diamond that had undergone color treatment through exposure to irradiation and annealing.

The GIA received a rough 3.93-carat, purple, type Ib diamond at its laboratory in Dubai for analysis. The stone displayed interesting growth patterns, according to an article in the spring issue of the institute’s quarterly journal, Gems & Gemology.

The findings showed that the diamond had received color treatment. This included a combination of irradiation and subsequent low-temperature annealing, which the GIA determined due to the stone’s intense bodycolor, diamond type and nitrogen-vacancy (NV) centers, to achieve a vibrant purple color, it explained.

DiamondView images revealed interesting patterns that provided further insight into the diamond’s growth history. Under deep ultraviolet (UV) illumination, a dark, nonfluorescing area resembling an arrow pointing toward the profile of an elongated diamond was visible. The remainder of the diamond showed bright orange fluorescence, likely associated with NV defects. This distinct pattern suggested multiple growth sectors formed during the diamond’s natural growth.

Purple coloration in diamonds is often attributed to transmission windows in the blue and red regions of the visible spectrum. In this stone, however, the introduction of NV centers produced an intense, pure purple bodycolor without the pink component commonly associated with NV-related coloration.

While arrow patterns created through polishing are often highly valued, this diamond presents a unique form of pareidolia – an inclusion resembling a recognizable form – with an arrow-like shape seemingly “hidden” within the stone. The pattern reflects the contrast between distinct growth sectors and becomes visible only under deep UV illumination.

Image: The purple-diamond examined by the GIA. (Gemological Institute of America)