Color intensification during sapphire color stability testing
CARLSBAD, Calif. – Dec. 13, 2022 – During routine color stability testing of sapphires, GIA experts observed an unusual gain of orange or yellow coloration to a padparadscha-like color or even to pure orange.
Color in sapphires can be unstable, which is why GIA routinely tests them, including those that may be characterized with padparadscha color, for stability by exposing them to intense incandescent illumination for a few hours. This test will cause an unstable orange component to fade, returning the stone to pink. In recently observed tests, some sapphires reacted to the color stability test by gaining orange or yellow coloration. Some pink sapphires might shift to a padparadscha color or pure orange.
This color change behavior raises important questions about determining and reporting the color of sapphires exhibiting this color change. In GIA’s experiments, the color observed after the color stability test is very similar to the color observed after exposure to daylight, for example, if set in jewelry and worn frequently. Given this and the need for a consistent, easily accessible standard, the color after the incandescent light stability test is the color indicated by GIA on reports for these sapphires. This standard is applied regardless of whether a sapphire loses or gains yellow or orange color during the test.
GIA’s preliminary observations and research into this important matter were recently published in a GIA Lab Note, An Update on Sapphires with Unstable Color, by GIA gemologists Dr. Aaron C. Palke, Shane F. McClure and Nathan R. Renfro. The full results of GIA’s research into this matter are currently being prepared for publication in Gems & Gemology, GIA’s quarterly academic journal, in the near future.
The latest issue and all previous issues of Gems & Gemology are available at GIA.edu.