March 6, 2026 · 7 min read
Understanding heat treatment in sapphires — what it means for value
Heat treatment is the norm in the sapphire trade, not the exception. Here is what buyers should know and what they should ask.
by Zabeh Ullah
More than 95% of sapphires on the commercial market have been heated. This is not fraud — it is an accepted industry practice, openly disclosed by reputable dealers. What matters is whether the treatment is disclosed at all, and whether the stone’s certificate reflects it accurately.
What heating does
Controlled high-temperature heating (typically 1600–1800°C) dissolves silk inclusions, improves color saturation, and removes undesirable secondary tones. A well-heated stone can appear dramatically more valuable than its unheated rough.
Unheated premiums
In fine-quality material above two carats, an unheated designation — confirmed by a major laboratory — commands a 30–80% premium over a comparable heated stone. For Kashmir and some Burmese material, the premium can exceed 100%.
What to ask
Always request a major laboratory report (GRS, Gübelin, SSEF, or GIA) that specifically addresses heat treatment. Any report that does not address this question is incomplete for serious buying purposes.
