Precious Stones · March 1, 2026 · By Maison Clara Rosae

It is estimated that more than 95% of sapphires traded worldwide have undergone heat treatment. High-temperature heating, between 1,200 and 1,800°C, improves or modifies a stone's color and dissolves certain inclusions, creating a more commercial appearance. It is an old, legal, and widely accepted practice in the trade. But it fundamentally changes the value of the stone.

What is an untreated sapphire?

An untreated sapphire, often called an unheated sapphire, is a stone that has undergone no thermal, chemical, or physical intervention to alter its appearance after extraction. Its color, clarity, and characteristics are exactly those nature gave it over millions of years of formation deep in the Earth's crust. This is not only a technical criterion; it is a statement of absolute authenticity.

How can it be detected?

The distinction between a heated sapphire and an untreated sapphire can only be established with certainty through gemological laboratory analysis. Reference gemological laboratories use spectroscopic analysis, microscopy, and UV luminescence to detect indicators of heat treatment, especially changes in mineral inclusions and dissolution halos around inclusion crystals. A gemological report explicitly stating "No indications of heating" is the only reliable guarantee.

Why is the value so different?

A fine untreated sapphire can be worth two to five times more than an apparently identical sapphire that has been heated, and sometimes far more for exceptional stones. This premium for authenticity reflects the increasing rarity of naturally beautiful sapphires with no intervention, as well as collectors' and investors' confidence in the long-term value stability of unmodified stones.

All sapphires offered by Maison Clara Rosae, yellow, star, and white sapphires alike, are rigorously untreated, sourced directly from Vietnam, and available with certification on request.