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Aaron C. Palke, Shane F. McClure, and Nathan R. Renfro wrote:An Update on Sapphires with Unstable Color Figure 1. A padparadscha sapphire (3.54 ct) submitted to the GIA laboratory increased its orange color during the color stability test. If left in the dark for an extended period of time, the color could become less orange or even go to straight pink. This can be replicated by exposing the sapphire to intense LED illumination. This stone would be characterized as a padparadscha sapphire because the pink-orange color after the stability test is acceptable. Photos by Diego Sanchez.
GIA has been performing color stability testing on some sapphires for decades (Crowningshield, 1969). More recently, the stability test has been implemented to identify pink sapphires that can be charged with UV light to create a temporary change of color into the orangy pink to pinkish orange range of padparadscha sapphires or even more orange in appearance. A few hours of exposure to intense incandescent illumination will cause the unstable orange component to fade away, returning the stone to a pink appearance. A sapphire will only be characterized as a padparadscha if the color is acceptable after this stability test. Temporary, unstable orangy pink to pinkish orange coloration does not qualify for the padparadscha characterization if the stone shows coloration outside of this range after the stability test. This change will also occur upon exposure to sunlight, although it takes longer. The color stability test and observations above are described in some detail by Nassau and Valente (1987), Krzemnicki et al. (2018), Smith et al. (2019), Hughes (2022), Wang et al. (2022), and Tsai et al. (2022). READ MORE
