GIA Analyzes a Purple Diamond Enhanced Through Color Treatment
The Gemological Institute of America (GIA) recently examined a purple diamond that had been artificially colored through a combination of irradiation and annealing.
The GIA received a 3.93-carat rough, purple, Type Ib diamond at its Dubai laboratory for detailed testing. According to an article published in the spring issue of the institute’s quarterly journal, Gems & Gemology, the diamond displayed unusual growth features that attracted the attention of researchers.
Laboratory analysis confirmed that the diamond had been color treated. GIA determined that the stone had undergone irradiation followed by low-temperature annealing. The treatment process, together with the diamond’s type, strong bodycolor, and presence of nitrogen-vacancy (NV) centers, was responsible for producing its vivid purple appearance.
DiamondView imaging offered additional information about the diamond’s internal structure and natural growth. When exposed to deep ultraviolet (UV) light, researchers observed a dark, nonfluorescent region shaped somewhat like an arrow and directed toward the outline of an elongated diamond. In contrast, most of the stone exhibited a bright orange fluorescence, which was likely linked to NV-related defects. The unusual contrast indicated that the diamond had developed through several distinct growth sectors.
Purple diamonds can sometimes owe their color to specific transmission windows in the blue and red portions of the visible spectrum. In this case, however, the presence of NV centers created a strong and pure purple color, without the pinkish tone that is often associated with NV-related coloration.
The diamond also offers an unusual example of pareidolia, in which a natural feature appears to resemble a familiar object or symbol. Unlike arrow patterns intentionally produced through polishing, the arrow-like shape in this diamond occurs naturally within its internal growth structure and can only be seen clearly under deep UV illumination. The feature highlights the contrast between the diamond’s different growth sectors and provides a fascinating glimpse into its formation history.
