A blue sapphire heated under pressure contains unusual fluid inclusions with mobile gas bubbles.
Mobile Gas Bubbles in Pressure-Heated Blue Sapphire
A 7.72 ct blue sapphire was recently submitted to our laboratory. We concluded that the stone had been heated with pressure from a combination of the FTIR spectrum, which displayed a broad band centered around 3047 cm⁻¹(figure 1) and inclusion features that showed clear signs of high-temperature heat treatment (Krzemnicki et al., 2019).
Figure 1. Infrared spectrum of a blue sapphire treated with heat and pressure, with a broad band centered around 3047 cm⁻¹.
Interestingly, we noted that the stone contained fluid inclusions with mobile gas bubbles, which moved when the stone was gently warmed with a hot point (see figure 2 and the video below). Normally sapphires heated at high temperatures don’t contain these mobile bubbles, as they tend to explode with high-heat treatment. However, in this case we hypothesize that the pressure helped to keep the inclusion intact. Mobile bubbles have been reported in pressure-heated sapphire (Ng-Pooresatien, 2020).
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Figure 2. A bubble is present in this fluid inclusion in a blue sapphire, which was determined to be treated with heat and pressure. With the gentle heat of a hot point, the bubble was observed to be mobile (see the different location of the bubble in the two images). Photo: E. Billie Hughes/Lotus Gemology. Field of view: 1.6 mm. |
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About the Authors
E. Billie Hughes is Co-Founder and Managing Director of Lotus Gemology, where she oversees the company's day-to-day operations while continuing gemological research and laboratory work. After graduating from UCLA, she became a Fellow of the Gemmological Association of Great Britain (FGA). Her research focuses on ruby and sapphire, including low-temperature heat treatment, and she has authored and co-authored articles in leading gemological journals. She has conducted fieldwork at gem deposits around the world, including nearly every major ruby and sapphire locality.
Billie is an internationally recognized educator who has lectured for trade organizations, museums, and luxury jewelry houses, including extensive educational work with Van Cleef & Arpels. She has also served as a judge on Thailand's The Secret Gems television series. An award-winning photographer and photomicrographer, her images have received honors in the Nikon Small World and Gem-A competitions and have appeared in publications including National Geographic and Forbes. She is also the creator of Hyperion, Lotus Gemology's online inclusion database.
Billie developed an interest in gemstones from an early age, accompanying her parents on expeditions to mines and gem-producing regions around the world. That lifelong passion for fieldwork, laboratory research, education, and photography continues to shape her work at Lotus Gemology today.
Natcha ('Ing') Rattana-anan has been interested in gems since childhood, which inspired her to study gemology at Chiang Mai University, where she did an award-winning thesis on heat treatment of amethyst. After graduating in 2024, she joined Lotus's gemological team.
Notes
This article first appeared in the Journal of The Gemmological Association of Hong Kong, 2026, Vol. 47.
References
- Krzemnicki, M.S., Cartier, L., Hughes, R.W., Leelawatanasuk, T., Kiefert, L., Choudhary, G., McClure, S., Milisenda, C., Gambini, E., Kim, S., Schwarz, D. and Horikawa, Y. (2019) Sapphires heated with pressure – A research update. InColor, Spring, pp. 86–90.
- Ng-Pooresatien, N. (2020) Lab Notes: Negative crystal containing a mobile CO₂ bubble in blue sapphire heated with pressure. Gems & Gemology, Vol. 56, No. 2, Summer, pp. 287–288.
