When you buy a sapphire, ruby or citrine, there is a good chance it has been heated. That is not a bad thing; it is one of the oldest and most widely accepted practices in the gem world. Here is what it means.
What is heat treatment?
Heating is a controlled process where a rough gemstone is warmed in a furnace to improve its colour or clarity. It recreates, in a few hours, conditions similar to those the stone experienced deep in the earth. People have been heating gemstones for centuries.
What does heating do?
- Improves colour: it can deepen the blue of a sapphire or remove a brownish tint from a ruby.
- Improves clarity: it can dissolve tiny silky inclusions that make a stone look cloudy.
- Creates colour: some stones change entirely. Most citrine on the market is heated amethyst, and tanzanite gets its violet-blue from heating.
Which gemstones are commonly heated?
| Gemstone | How common is heating? |
|---|---|
| Sapphire | The great majority |
| Ruby | The great majority |
| Tanzanite | Almost always |
| Citrine | Very common (often heated amethyst) |
| Aquamarine | Common, to remove a green tint |
| Blue topaz | Treated to create the blue colour |
| Emerald | Rarely heated; usually oiled instead |
Is heat treatment permanent?
Yes. The colour and clarity from heating are stable and will not fade with normal wear. Heated stones need no special care beyond what you would give any gemstone.
Does heating affect value?
Heated stones are the market standard and are priced accordingly. A rare, natural, unheated sapphire or ruby of top colour can command a significant premium, and it should come with a lab report to prove it. For most beautiful everyday jewelry, heated stones give you vivid colour at a fair price.
Heated vs other treatments
Heating only uses heat. Other treatments, such as glass filling, diffusion or dyeing, change the stone in less stable ways and should always be disclosed. If you are ever unsure about a stone, ask the jeweler directly; a good one will tell you.
Frequently asked questions
Is a heated sapphire a real sapphire?
Yes. It is a natural sapphire that has been enhanced, not a synthetic or imitation stone.
Can you tell if a stone is heated by looking at it?
Usually not. Gem labs use microscopes to look for signs of heating inside the stone.
Explore our gemstone jewelry, including sapphire and ruby pieces, or ask us about any stone when you visit the boutique.
