Among fancy sapphires, orange is one of the most controversial colors. Long coveted for their rarity, these sapphires have their own historical provenance, Sri Lanka, the country of origin that made them well known in the West as “padparadscha”. The name in itself carries some ambiguity: “padparadscha” is derived from the Sanskrit “Padma”, meaning a color similar to the pink lotus flower (Nelumbo Nucifera ‘Speciosa’). It is a fact that most lotus flowers are much more pink than orange. Therein lies the problem, that is, the separation line between pink and orange in fancy sapphires, a very sensitive issue since the market unquestionably assigns a substantial premium to orange sapphires.
Orange sapphires again came into the spotlight of gemological investigation at the beginning of the new millennium, when an unexpected quantity of sapphires showing a very attractive, often intense, orange hue, appeared on the market. The market reacted enthusiastically, though it had to take a step back later when gemological laboratories found that the intense orange, suddenly so abundant and accessible, resulted from an all-new treatment.
It was the deep diffusion of chromophore trace elements into fancy sapphires. This treatment allowed for an orange hue and greatly altered the original color.
However, today gemologists and traders working on orange sapphires must take into account something new. The SSEF laboratory published a note in March 2022 introducing a new topic that certainly can challenge the work of proper identification and disclosure. The Swiss lab had the opportunity to test some samples of natural but unstable fancy sapphires that show different colors depending on light conditions. The dissolution effect in natural light is reactivated by UV light, a phenomenon known as tenebrescence. As a result of tenebrescence, some fancy sapphires presented in the laboratory showed a marked change in color over time, changing from a pinkish orange to a noticeably pink hue within a few weeks. The phenomenon is reversible when the sapphire is exposed to UV light again.
The stable color of the gemstones tested is indeed pink, determined by chromium. Associated with it is an overlapping unstable color, yellow. The instability of the yellow color is due to structural defects at the atomic level that, when activated, turn the overall color of the stone from orange to pink.
A strong reduction (dissolution) of the yellow color center is attested by spectrometric investigations conducted by SSEF before and after dissolution tests.
The gemstones under consideration come from Ambatondrazaka in east-central Madagascar, a site that in recent times has produced an impressive range of both blue, sometimes very fine, and fancy sapphires.
The SSEF note comes to the conclusion that – given the instability of the orange color – it is not possible to describe gems exhibiting these characteristics as “padparadscha” and that it is appropriate to describe them as fancy sapphires.
Gem News published on IGR – Italian Gemological Review #15, Autumn 2022.
