Price data
The unheated sapphire premium
Unheated stones carry a premium because untreated colour is scarcer: typically two to five times the price of an equivalent heated stone, and wider as the stones get bigger.
The guide
What is the premium worth in dollars?
All figures are approximate US dollars per carat, indicative retail, for eye clean Ceylon blue of good to fine colour, the reference type. The full matrix of every type and weight sits on the price by carat page.
| Weight | Heated | Unheated |
|---|---|---|
| About 1 carat | US$ 300 to 1,800 | US$ 350 to 4,000 |
| About 3 carats | US$ 850 to 5,000 | US$ 1,500 to 10,000 |
| About 5 carats | US$ 2,000 to 9,000 | US$ 3,000 to 18,000 |
| About 10 carats | US$ 4,000 to 15,000 | US$ 8,000 to 40,000 |
General market figures drawn from published trade and gemmological guides, last reviewed August 2026. They describe the wider retail market, not our listings; every stone on this site is priced on its own listing against its own report.
The furnace
What does heat treatment do?
Heat treatment improves colour and clarity in corundum by taking the stone to a high temperature under controlled conditions. It can deepen a pale blue, clear the fine rutile silk that clouds a stone or move an iron coloured stone towards the hue the market asks for.
A heated stone is still natural corundum. Heat is long established trade practice and it changes the stone without changing the mineral it is; what matters is that it is disclosed. Every listing here states heated or unheated exactly as the laboratory report does.
The scarcity
Why does unheated carry a premium?
Because a stone that reached its colour in the ground is scarcer than one brought there in a furnace. Most corundum out of the gravels needs help, so material fine enough to leave alone is a small share of what is mined.
Demand pulls the same way. Many buyers ask for unheated specifically and a laboratory report is the only thing that settles the question, so the premium attaches to stones whose reports state no heat. In general terms the gap runs about two to five times, widening with size.
The proof
What does the report state about heat?
It states whether the laboratory found evidence of heat, in the words that laboratory uses. That is a finding about the stone in front of the gemmologist rather than a history of it, and it is the only evidence worth pricing on.
A stone here with no report issued shows as pending, carries no price and is never assumed either way: a stone is recorded as unheated only where its report says so.
Questions
Asked about heat and price
If a question about treatment is not answered here, write to Colombo and a gemmologist replies, not a template.