Low-Temperature Heating of Pink Sapphire: Why Detection Can Be Difficult

A pink sapphire with a violet component may become a cleaner pink after heating. Detecting this change can be difficult when the heating leaves little obvious damage inside the stone. The word low-temperature is relative: the temperatures involved are still extremely high.

What the experiments showed

SSEF’s 2010 article describes research on pink sapphires from Madagascar and East Africa. Heating around 800–1000°C could reduce the blue component. The researchers also studied samples at several lower and higher experimental temperatures.

The important lesson is that familiar microscopic signs of intense heating can be scarce after lower-temperature treatment. A stone that lacks melted-looking inclusions is not automatically proven unheated.

Zircon inclusions as evidence

The study investigated zircon inclusions with Raman spectroscopy. Heating could alter their crystal condition and the shape of their spectral peaks. Measuring these changes provided evidence that was less obvious in ordinary microscope views.

This does not mean every sapphire contains suitable zircon, or that one numerical result works as a universal heating thermometer. The method must be applied to the right material and interpreted with other evidence.

Read report wording carefully

Ask what treatment conclusion the laboratory reached and whether its examination addressed subtle heating. Colour photographs cannot establish an unheated status. This article explains a historical research approach and does not claim that one laboratory alone uses the technique today.

Sources and further reading

SSEF Swiss Gemmological Institute, Facette, issue 17, January 2010, pp. 12, “How to get the “Blues” out of the Pink”. Read the original SSEF PDF.

This independent educational article explains historical SSEF research in original, simple English. It is not an SSEF publication. No source photographs or illustrations are reproduced.