The unheated gemstone buzz, explained

By Livia Primo Lack

5 minute read

As jewellery lovers, recent weeks have seen our Instagram feeds flooded with images of colourful and vibrant Couture gems.

After all, it’s summertime, and with that sunshine holiday spirit comes a desire to select brighter and bolder accessories. Speaking of rising temperatures, the buzz words “unheated”, “no heat” and “untreated” are terms that are increasingly present in jewellery campaigns, especially when it comes to cardinal gems like rubies, sapphires and emeralds. 

But what do these terms actually mean? With the help of Josephine Odet, Lymited’s Head of Jewellery, we’re here to break it down.

What is the thermal enhancement of gemstones?

All gems are ‘treated’ in some form or another; very few brands are taking a rough uncut gem and setting it directly into a piece of jewellery. Most natural gems are found in their earthen state, and are then cut, polished and transformed into various shapes. The word “treated” usually refers to processes that the stone undergoes once it has passed through those preliminary procedures. One of the most common treatments is thermal enhancement: the process by which gems are exposed to high temperatures in order to enhance and improve their colour and clarity (two of those oh so important ‘4Cs’). 

Heating gems to intensify their physical colour is a treatment that has been around for hundreds of years, however it became widespread in the 20th century, thanks to industrialisation and the ability to make larger quantities at a faster rate. The result of thermal enhancement is a mostly stable stone with a permanent colour change. 

This technique has become synonymous with some gemstones, such as tanzanites, which have a natural brownish hue, but when heated transform into a unique purplish blue colour. For rubies, heating cancels out the purple in their colouring, allowing the gem to get as close to that perfect ‘pigeon blood red’ as possible. It also removes their occasional silk-like inclusions, making the ruby appear more opaque. The same goes for sapphires, however heating them can also onset their blue colour, if it’s not their natural hue. In fact, 99% of gem-quality sapphires set in jewellery in the world have undergone thermal enhancement. 

Why are we seeking unheated gemstones?

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Top: Tiffany & Co, Sapphire & Diamond Ring, 1920s. Above: Ana De Costa, Pearl and Garnet Earrings

Why are we seeking unheated gemstones?

While it has become commonplace to heat gems, it is often considered a coup to have an unheated gemstone, especially when it comes to those that are larger in size and more important in rarity, such as rubies and sapphires.

Their higher value stems from their rarity. Finding a larger, more important gem, that has not undergone thermal enhancement, with an intense and vivid colour is a “perfect storm”, says Odet. So many uncontrollable factors in nature need to go right for this to happen. “In jewellery, you’ll find that 90% of coloured stones are heated or have had some sort of treatment. I look for the elusive 10% that haven’t,” Odet explains.

How to determine if a gemstone is unheated?

Josephine Odet Jewellery Expert
“In jewellery, you’ll find that 90% of coloured stones are heated or have had some sort of treatment. I look for the elusive 10% that haven't,” says Lymited's Head of Jewellery, Josephine Odet

How to determine if a gemstone is unheated?

Odet advises that while it is completely acceptable for a buyer to ask whether a stone is heated, “there is a time and a place”! 

Firstly, it’s important to know that determining and certifying whether a stone has undergone thermal enhancement is a financial investment for the jeweller. Getting a trusted gemological report for a gemstone stating whether it is unheated could cost them between £200 to £500. So, don’t bother asking about heating when it comes to smaller pavé stones, since it’s highly likely they will be uncertified. If this is the case, it comes down to a matter of trust between you and your jeweller. Ask them about the “origin” of the stones, rather than if they are heated. An open-ended question will get you a lot more information (geographical provenance, ethical practices and materials, overall treatments) than a simple yes or no. 

Secondly, ask yourself what period you are purchasing from. Important gemstones set into contemporary pieces will often be accompanied by a gemological report stating treatment (if any). However, for Georgian (1714-1837), Victorian (1837-1901) or Edwardian (early 20th century) pieces, un-mounting a gemstone may be more complicated due to the setting type or design, and removing a gem may damage the piece irrecoverably, diminishing its value. In cases like this, you can get a verbal certification from labs – or take your specialist’s word for it. 

 Facet And Fable Pink Topaz And Diamod Pendant Earrings Ja0048 Collection Nfp
Edwardian Pink Topaz and Diamond Earrings – finding one pink topaz with a richly saturated colour and of a significant carat weight is difficult, but to find a matching pair is exceptional

What’s driving the need for gemological reports?

The price of gems relies on their identity, colour, clarity, weight (carat), size, origin, shape, treatments, cut, and polish. Naturally occurring, flawless, large gemstones are often the most valuable, but are also the rarest. With natural, unenhanced gemstones realising increased price per carats, gemological reports that accompany the gemstones, from reputable laboratories, are essential.

Increasingly, consumers and jewellers alike are calling for these gemological reports. While there is a huge demand for gemstones, regulation has struggled to keep up, and as a result, the volume of fraudulent gems has increased. An effective and fast way of determining authenticity is therefore crucial. In short: a gemological report or specialist opinion is there to protect the consumer.

Lymited's selection of untreated gemstones

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Racine, 'Lotus' Ring , featuring a rare Padparadscha sapphire of natural orangey-pink hue

Lymited's selection of untreated gemstones

The selection of coloured stones on the Lymited platform are a mix of certificated and antique jewellery, all sourced by Odet. “Of our jewels featuring coloured gemstones, 90% have not undergone any thermal enhancement or treatment. It’s the complete opposite of what’s happening in the rest of the marketplace,” she explains. 

From antique natural topaz to a vintage Cartier ring, set with a certificated Columbian emerald, and an important Ceylon sapphire in a Deco Tiffany & Co. ring  – all from the collection of fine gem connoisseurs Facet & Fable – plus pieces by contemporary designers Racine and Ana De Costa, who go that extra mile to source unheated gemstones, this is a selection you can trust.   

However, keep in mind that perceiving colour is an incredibly subjective experience. We advise that you be informed on the stone’s origin, but don’t let it consume your purchase decision. “At the end of the day, the most important thing is that you buy a piece that speaks to you personally,” Odet concludes.

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