GIA Detects ‘Quench-Crackle and Dye’ Treatment in Lab-Grown Sapphire

The Gemological Institute of America (GIA) recently examined a colorless lab-grown sapphire that showed signs of “quench-crackle and dye” treatment, a common color-altering procedure.

The 12.65-carat synthetic gemstone arrived at GIA’s laboratory in Carlsbad, California, to undergo investigation for color treatment, according to an article in the fall issue of the institute’s Gems & Gemology quarterly journal.

The quench-crackle and dye technique, which first appeared in the 1990s, involved quenching a heated stone in room-temperature water, creating fractures that allow dye to enter and alter the gem’s color. This treatment most often takes place on quartz, cubic zirconia, glass, and other synthetic gemstones because they are low-cost, widely available materials.

Initially, it appeared that the stone was a Paraiba tourmaline or a low-quality emerald. While the dye-filled fractures were faintly visible to the naked eye, routine gemological testing identified the stone as sapphire. The absence of natural inclusions and X-ray fluorescence results showing no gallium or iron confirmed it was a laboratory-grown stone.

Visible/near-infrared (Vis-NIR) absorption spectroscopy revealed a broad absorption band, which does not occur in naturally colored corundum and explains the sapphire’s artificial color. Microscopic examination showed evenly spaced, web-like fractures characteristic of quench-induced treatment.

Image: The lab-grown sapphire examined by the GIA. (Gemological Institute of America)