Heat Treatment
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Definition
The controlled heating of a gemstone to high temperatures to improve or alter its color, clarity, or both, by inducing or dissolving inclusions and changing trace element oxidation states.
Detailed Explanation
Heat treatment is the most widespread gem enhancement and is considered 'accepted' by the international gem trade when properly disclosed. Pale blue sapphires from Sri Lanka are heated to over 1,800°C to dissolve rutile silk and improve transparency. Yellow sapphires are heated under reducing conditions to produce blue by reducing Fe3+ to Fe2+. Rubies from Mozambique are heated to dissolve fracture-filling flux and improve clarity. Most sapphires and rubies on the market are heated. Advanced lab testing (infrared spectroscopy, photoluminescence) can sometimes detect heat treatment evidence.