The briefest exposure to a UV lamp immediately altered the colour of this synthetic sapphire.
Gem Note: Ni-bearing Synthetic Sapphires Showing Irreversible Photochromism, Journal of Gemmology 2025, Vol 39 (7): 629-631
Authors: Sean O’Neal, Charles Evans FGA DGA, Guy Borenstein FGA
In this paper we looked at a new shade of synthetic sapphire that was being considered for sale and undergoing quality testing. Synthetic sapphire is a product in increasing demand due to affordability and consistency in colour as well as the typical corundum attributes like hardness and luster. It is also interesting how there is strong demand for non-standard sapphire colours, like this “aqua” material. We noticed that the briefest exposure to a UV lamp immediately altered the colour. Given the widespread use of UV lights in gemstone testing we felt it important to report this. The appraiser in me could just imagine an appraisal where I would shine a UV torch over a client’s ring as a matter of course to see if the response raised any red flags and then feel the absolute horror of having altered the colour of the gemstones. During this investigation, we also discovered how difficult it is to track down the actual manufacturing facility of the original boules.
Incidentally, in the months after publication we were able to reverse this colour change, but it took many hours of exposure to incandescent light, and we were not completely convinced that the restored colour had the same degree of saturation.
Gem Note on Coloured Stones, featured in The Journal of Gemmology, Volume 39, No.7, published in 2025.
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