Why We Roast Rocks: The Hot Truth About Heated Corundum

At FNG, we believe beauty should be brilliant-but also honest.

Let’s set the record straight: heating corundum (aka ruby and sapphire) is not some gemstone gimmick. It’s a standard, respected practice-kind of like polishing silver or decanting wine. We do it to bring out the very best in these precious stones. Not to deceive, but to enhance.

Why heat corundum?

Because nature sometimes needs a nudge.

Rubies and sapphires form deep in the Earth under intense heat and pressure. But when they emerge, they don’t always look like the showstoppers they were born to be. Some might have a haze, a bit of silk, or a less-than-vivid hue. So what do we do?

We give them a spa day.

A controlled heat treatment—done without additives—can:

• Intensify color (like turning a soft pink into that perfect pigeon-blood red),
• Improve clarity (by dissolving microscopic inclusions),
• And heal tiny fractures (basically gemstone skincare).

It’s completely stable, permanent, and accepted throughout the fine jewelry industry. In fact, a majority of corundum on the market-yes, even in luxury collections-has been heated. It’s not a secret. It’s science.

But not all treatments are created equal…

Here’s where it gets spicy. When we talk about other treatments-like lead-glass filling, beryllium diffusion, or synthetic color enhancements-we’re in very different territory. These methods don’t just enhance the gem, they alter it. Sometimes dramatically. Sometimes irreversibly.

And worst of all? They often don’t stand the test of time.

Those flashy colors can fade. The fillings can crack. And the stone? It’s not what it pretended to be. It’s the gemstone version of a knockoff designer bag. Not our style. Not yours either.

Heat is honest.

A heated ruby is still a real ruby. It’s still a treasure of the Earth. It’s just had a little human guidance to reach its fullest potential-like taking a great photo in natural light. No filters, no fillers. Just brilliance.

At FNG, we’re proud to offer stones that are responsibly sourced, transparently treated, and undeniably gorgeous. Because when you’re investing in fine jewelry, you deserve the truth-and a little fire.