One of the questions we hear often, especially when clients are comparing sapphires side by side, is some version of this: "These two stones look nearly the same. Why is one so much more expensive?"
The honest answer is that size is only a small part of what makes a sapphire valuable. One of the biggest differences you'll encounter, especially in fine and investment-grade stones, comes down to treatment.
Most sapphires are heat treated
Heat treatment has been part of the gemstone trade for centuries. The process is exactly what it sounds like: rough sapphires are exposed to high temperatures, which improves colour and clarity in a stable, permanent way. There's no coating, no filling, no synthetic material introduced. A heated sapphire is still a natural sapphire. It came out of the earth, it was just given a little help reaching its most beautiful potential.
The majority of sapphires on the market are heat-treated, because a beautiful-looking heated stone is generally considered more desirable than a less beautiful untreated one, making heat treatment a default choice for most mines. It's not a mark against a stone, and in fact, heated sapphires are an excellent choice for many people depending on their colour, clarity, size, and budget preferences.
What "unheated" actually means
An unheated sapphire is one that came out of the earth already as it is; no heating or enhancement. The colour and clarity you see are entirely natural. Because heated sapphires are the standard, we call these stones unheated.
This matters because very few sapphires are naturally clean and beautifully coloured enough to skip heat treatment. Most sapphire rough has uneven colour, visible inclusions, or a murky, grey-brown tone before heating. The stones that emerge from the earth already vibrant and clear are genuinely rare. That rarity is where part of the premium comes from, and as sapphires get larger, that rarity increases exponentially.
The misconception
When it comes to stone cost, "no-heat" alone does not automatically make a sapphire valuable.
A dull, heavily included, poorly coloured unheated sapphire can easily cost less than a vivid, well-cut heated one. An unheated designation is only one factor among many, and overall quality is always the most important factor.
When two stones are genuinely similar in colour, clarity, cut, size, and origin, the unheated stone usually carries a premium when comparing against the heated option, simply because the unheated stone is much more rare. In gemstones, small details can create very big price differences, and treatment status is one of the details that collectors and connoisseurs weigh carefully.
What this means when you're choosing a stone
Whether or not a sapphire has been heat treated is something only you will really know, since there's no obvious visual indicator to mark it. If you're looking for a sapphire for an engagement ring or a special piece, we always recommend looking for something that you and your partner find beautiful above all else. Everyone has different preferences and priorities, and oftentimes finding a sapphire with the perfect colour is much more important than finding one that's untreated. Both heated and unheated sapphires are real and natural, and both can be extraordinary.
Where treatment status becomes a serious consideration is when you're comparing two high-quality stones that are otherwise similar, or when you're thinking about a stone as a long-term investment. Certified no-heat stones with fine colour carry a premium precisely because all of the conditions lined up perfectly during its formation without any human intervention, which can be exponentially more uncommon depending on the colour you're looking for. If your budget allows it and you find the right stone that meets all of your preferences without any treatment at all, then it can be worth paying for.
At the studio, we work with both heated and unheated sapphires. When a stone's treatment status is known and relevant, we'll always tell you. And when we're sourcing for a bespoke piece, we're happy to look specifically for certified no-heat stones if that matters to you… but restricting your search to only include unheated stones will significantly limit the options we can show you, and will exclude some beautiful stones that might otherwise be perfect, so it's worth carefully considering how much that designation means to you.
As with most things in fine jewellery: the more you understand what you're looking at, the better the decision you'll make. ✨
A note on other treatments
It's worth knowing that heat treatment is far from the only way sapphires can be enhanced. More invasive treatments exist and are important to understand, because they represent something quite different.
Glass or Flux filling, for example, involves heating a stone with a chemical compound that melts into its fractures and cavities to improve apparent clarity. This can make an otherwise poor-quality stone look much better, but the improvement is superficial and the stone may be fragile as a result.
Beryllium diffusion is a newer technique where the element beryllium is introduced during heating, penetrating the stone and artificially changing its colour. Stones that have obtained their colour this way are considered to have little intrinsic value.
Irradiation (radiation treatment) can induce vivid yellow or orange hues in pale stones, but the colour is often unstable and fades with light or heat exposure over time.
These treatments are fundamentally different from standard heat treatment. They introduce foreign materials into the stone, change its chemistry, or produce results that aren't stable or permanent in the way that heat treatment is. This is why disclosure and reputable sourcing matter so much in the sapphire trade. At Laurie Fleming Jewellery, we only work with heated and unheated natural sapphires. We do not work with sapphires that have been treated in other ways.
FAQ
Are heated sapphires fake or synthetic?
No. A heated sapphire is a natural sapphire. It formed in the earth over millions of years; it was simply treated after mining to improve its colour and clarity, like putting a tray of brownies back in the oven because they weren't quite ready 😉 Synthetic sapphires are grown in a laboratory in a completely man-made process. Heat treatment does not change a stone's natural origin.
Laurie Fleming Jewellery doesn't work with lab grown or synthetic sapphires (or other coloured gemstones) because we find that they often lack the charm and character of natural sapphires, with colours that look a bit too bright/saturated/synthetic (at least with current technology).
How do I know if a sapphire is heated or unheated?
We will always disclose the treatment status on our sapphire centre stones. For our sapphire melee, all stones are very likely heated. When we source our sapphires, our trusted trade partners always disclose treatment status.
You can also use a certificate from a reputable gemological laboratory to be sure, with the GIA and AGL being the most trusted for sapphires. The certificate will note whether heat treatment was detected, not detected, or inconclusive.
Does heat treatment affect how durable a sapphire is?
No. Heat treatment is a stable, permanent process. It doesn't make a sapphire more fragile, more prone to chipping, or less suitable for everyday wear. A heated sapphire set in a ring will hold up exactly as well as an unheated one. In fact, because heat treatment can dissolve impurities in a sapphire (improving the clarity), a sapphire may be more durable after heat treatment than it was before, if the inclusions were creating weak points.
Is an unheated sapphire always worth more?
Not automatically. A poorly coloured, heavily included unheated stone can cost less than a vivid, clean heated one. The "no-heat premium" only applies meaningfully when two stones are genuinely comparable in colour, clarity, cut, size, and origin. Quality and beauty will always be the most important.
Should I always ask for a certificate when buying a sapphire?
A certificate from a reputable lab is the only way to verify treatment, origin, and quality independently. For smaller accent stones or lower price points, certification is less common and not always necessary, but it's always reasonable to ask what is known about a stone's treatment status.
That being said, most sapphires are not certified (or come with a certificate from a local lab that is not reliable), and in order to have a sapphire certified by the GIA, it must be sent to their lab before being set in a ring in a process that can take several weeks, with associated costs that can vary.
We generally don't recommend having a sapphire certified unless the stone is extremely high-value and investment-grade. A sapphire ring can still be appraised and insured without a certificate for the sapphire itself, and unless you have a completely open deadline for your bespoke piece and don't mind paying the additional costs associated, it's generally not something we consider necessary.
Ultimately, it's up to you, and we're happy to help walk you through the process if you decide you want to go that route.
Do you work with unheated sapphires at LFJ?
Yes, we do work with both heated and unheated sapphires. If you're specifically looking for a no-heat stone for your bespoke piece, just let us know when you reach out. We'll search with that in mind, though availability varies and no-heat stones in fine colours take longer to source, or may not be possible to find in the size/shape/budget you're requesting.
Do you work with sapphires that have undergone other treatments, like diffusion or fracture filling?
No. At Laurie Fleming Jewellery, we only work with heated and untreated (unheated) sapphires. We don't work with stones that have been treated through processes like beryllium diffusion, glass filling, or irradiation.
These treatments are fundamentally different from heat treatment. Rather than enhancing what's naturally present in the stone, they introduce foreign elements, fill fractures with chemical compounds, or induce colour that may not be stable over time. A beryllium-diffused stone isn't a naturally coloured sapphire that was gently improved; it's a stone whose colour was created artificially, and it's priced accordingly. Instead, we focus on finding extraordinary, natural sapphires, heated or unheated, with beautiful colouring and fine quality.