A REMARKABLE "OTTU" SAPPHIRE AT THE LABORATORY
The analysis of the 7.91-carats 'Ottu' sapphire developed in this article could be considered a classic gemmology exercise for all enthusiasts.
The concentration of blue colour in a thin layer of the sample gives the appearance of a doublet. However, this particular type of sapphire, which is well-known to Sri Lankan lapidaries, is not a composite but a single gemstone.
This remarkable stone provides an opportunity to revisit the origin of the word 'Ottu', traces and interpretations of which can be found in Dravidian languages.
It has been demonstrated through meticulous observation that the presence of blue calcite inclusions has been identified in conjunction with colourless calcite, thus indicating an unconventional crystallisation process.
Microscopic observations and other spectral analyses indicate a probable origin in Sri Lanka, where these 'Ottu' sapphires are traditionally encountered in the market.
Authors:
- Clara Allirol-Mouton, GGTL Laboratories Switzerland
- Franck Notari, GGTL Laboratories Switzerland
- Féodor Blumentritt, GGTL Laboratories Switzerland
Read the full article in Gemmes from Gemmologie and Francophonie:
https://gemmologie-francophonie.com/la-revue-gemmes/
Allirol-Mouton C., Notari F., Blumentritt F. (2025) A remarkable "Ottu" sapphire in the laboratory. Gemmes, 6, pp 10-21.