Heated or Unheated Sapphire: What Is the Difference and Which Should You Choose?
When you buy a sapphire, one detail appears on every certificate: heated or unheated. This simple note can multiply the price of a stone by a factor of three. Here is everything you need to know to make the right choice.
What Is a Heated Sapphire?
Heating is the oldest and most widespread treatment in gemmology. The stone is brought to very high temperatures (often between 800 and 1,800 °C) to intensify its colour and improve its clarity by dissolving certain inclusions. The treatment is stable, permanent and accepted by the market: it is estimated that more than 90% of the sapphires sold worldwide are heated.
What Is an Unheated Sapphire?
An unheated sapphire is a stone whose colour and clarity are entirely natural, exactly as the earth created them. No human intervention has altered its appearance, apart from cutting. It is a rarity: only a small fraction of the sapphires mined show a colour beautiful enough to be sold without treatment.
What Impact Does This Have on Value?
For equivalent colour and clarity, an unheated sapphire is worth significantly more than a heated one. Why? Because rarity drives value. An intense blue sapphire, eye-clean and certified unheated, is an exceptional stone, sought after by collectors and jewellers alike. It is also the category of stones that best holds its value over time.
How Can You Tell Whether a Sapphire Has Been Heated?
It is impossible with the naked eye, even for a professional. Only a gemmological laboratory can determine it, by analysing the stone's internal inclusions under the microscope and by spectrometry. That is why it is essential to buy a sapphire accompanied by an independent laboratory certificate that explicitly states the absence of thermal treatment ("no indication of heating").
Which Should You Choose?
- For an everyday piece of jewellery on a controlled budget: a heated sapphire is an excellent choice. Its colour is stable and its beauty identical to the eye.
- For an exceptional piece, an investment or an heirloom: choose a certified unheated sapphire. Its rarity makes it a safe value.
Our Commitment
At Maxime Voillot Gems, we source our stones directly at the mine, and the vast majority of our sapphires are unheated and certified. Discover our selection of sapphires and blue gems, our exceptional stones, or book an appointment at our Paris office to admire them in person.
