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Beauty under pressure: Deciphering the cost and payoff for sapphires treated with HPHT

By Diana Jarrett

From left: 7-carat sapphire with no heat treatment; 9-carat sapphire with conventional heat treatment; and 7- and 9-carat sapphires with high pressure. high temperature (HPHT) treatment. Photo courtesy GRS Laboratories
From left: 7-carat sapphire with no heat treatment; 9-carat sapphire with conventional heat treatment; and 7- and 9-carat sapphires with high pressure. high temperature (HPHT) treatment.
Photos courtesy GRS Laboratories

Most working in the industry are aware sapphires are routinely treated to increase their marketability. What many dealers, manufacturers, and retailers may not be aware of, however, is a relatively new treatment used to beautify unattractive sapphire: high pressure, high temperature (HPHT).

While heat application is an ancient method for pushing corundum (the mineral species of sapphire) to produce its best colour, cooking alone does not always deliver the suppliers’ desired results. The added procedure of applying highly concentrated pressure to these stones, however, can provide astonishing results and produce vibrant, beautiful cobalt gems.

Broken fragments of a cabochon stress-tested by a hammer create triangular fragments with cracks radiating toward the centre of the stone. Photos courtesy GRS Laboratories
Broken fragments of a cabochon stress-tested by a hammer create triangular fragments with cracks radiating toward the centre of the stone.

As with every gemstone procedure, this treatment carries benefits and caveats. The advantages are obvious: stones having been subjected to HPHT treatment take on a lively saturated blue hue that makes for attractive jewellery pieces. The downsides, unfortunately, are still being determined.

A global appearance

More than six years ago, evidence began to emerge of HPHT-treated stones having entered the global market.

“We were aware of this treatment,” says Mayur Patel, a gemmologist with Toronto-based Byrex Gems, Inc. “We encountered some stones in the Hong Kong show and Bangkok in mid-2016.”

At the time, the application was not identified and, with no frame of reference, it was not easy for professionals to discern the true state of the goods.

“We were confused as to why they were coming about 25 to 35 per cent cheaper than the regular stones of same quality [done by] conventional heating,” Patel says.

GemResearch SwissLab (GRS) founder Adolf Peretti, PhD, FGG, FGA, sheds light on the early days of these gems.

“The stones first appeared in Sri Lanka when dealers contacted us in 2015,” he says. “They explained that previously untreatable rough was being bought up, treated, and resold at lower prices, so they thought it may be a new diffusion process.”

The heat is on

In a bid to help the colour of unattractive sapphires reach marketable tone, these stones may have been subjected to numerous heat treatment sessions prior to undergoing HPHT methods. Indeed, when it comes to evaluating a treated sapphire, there is no telling how many times a stone has been previously subjected to heating events.

Before these techniques emerged, sapphires were heated to temperatures of 1500 to 1800 C (2732 to 3272 F)—yet some stones still resisted enough improvement to be salient. Using HPHT, stones were confined in devices at around 1 kbar (1000 bars) of applied pressure for 15 to 30 minutes, which created a product dealers are able to sell to interested customers.

Discovery in the market

A diamond technology production factory in St. Petersburg, Russia, with more than 30 cubic presses for largescale application of new HPHT technology.
Photo courtesy NDT

When these unknown sapphires appeared at trade shows, buyers were eager to understand what they were working with.

“Some dealers submitted single stones in Bangkok,” Peretti says. “After receiving HPHT reports, they did not return with more of the same stones.”

Since the treatment reflected new territory in the gem world, there was some reticence to purchasing these goods until the trade learned more.

“They knew how to avoid buying the material in Bangkok,” Peretti adds.

This same caution, however, had not yet permeated the North American market.

“In New York, buyers didn’t know anything about the material,” Peretti says, “and stones were eventually detected as being included in high-value lots.

“The dealers were surprised and shocked to discover these ‘hidden’ stones. [It was] considered a scandal.” 

Patel echoes Peretti’s concerns, noting he was one of many industry members who exerted caution at that time—especially, he notes, because of the importance of gemstone origin reporting.

“With a bit of research in the market, we came to know about this treatment and we were shocked,” Patel says.

“We were scared of mistakenly buying such stones. What if we sold those to our respected customers unknowingly? We are well-known for supplying gem stones with the right information. It’s very necessary to disclose to our customers what sort of treatment is done on a particular stone.”

Detection and observations

GRS Labs managing director, Willy Bieri, performing microRaman analysis at the laboratory’s headquarters in Meggen, Switzerland. Photo courtesy GRS Laboratories
GRS Labs managing director, Willy Bieri, performing microRaman analysis at the laboratory’s headquarters in Meggen, Switzerland.
Photos courtesy GRS Laboratories

Upon careful inspection, differentiation is made between conventionally heated stones and those subjected to HPHT treatment. When using a Fourier transform infrared (FTIR) microscope, the characteristic colour zoning (or halo rims) reveal 3D fractures around crystal inclusions. Brownish staining in the fractures is also observed in HPHT-treated stones.

The HPHT-producing blue rims in iron-rich stones are a few millimetres deep in some treated sapphires; in other instances, these can infiltrate the centres. Material in the medium-colour ranges might appear to be evenly zoned throughout.

Identification

The high-pressure treatment itself appears to be stable; however, because the stones undergoing this treatment are often native cut, they are typically re-cut more precisely to conform to Western preferences. This runs the risk of compromising some of the concentrated blue colouration on the outside rim of the stone. Further, treated stones may be more brittle, which poses significant difficulty when they are re-cut for jewellery making or during a repair. 

As more HPHT-treated sapphires enter the market, it is important to ensure these stones are identified (and disclosed) before they’re sold. This identification, however, requires specialized equipment, and most labs have yet to invest in this critical technology.

At GRS, Peretto notes, FTIR microscopes are used to plot and measure tiny, localized points along the stone, which helps separate spectra from its different sectors. The rim of a stone treated with high-pressure bears an HPHT signature, while its core exhibits a signature more aligned with a conventional heated stone. Above all, a trained eye and microscope can independently verify the findings.

Micro-photo internal signature of an HPHT-treated sapphire shows pinpoint-type fluid inclusions feathers with extension cracks marked by thin white films.
Micro-photo internal signature of an HPHT-treated sapphire shows pinpoint-type fluid inclusions feathers with extension cracks marked by thin white films.

It’s worth nothing that simply because these treated sapphires entered the market under the radar, this doesn’t necessarily suggest malice on behalf of the manufacturer; more likely, the intent was simply to offer a wider range of salable goods at attractive prices.

“The manufacturer sought to treat material that was previously lower quality, untreatable, and, therefore, unsalable—for example, stones with fluid inclusions or goods unreceptive to conventional heating methods,” Peretti says. “Ultimately, they were looking for a cheaper sapphire material that was available in large quantities.”

The ideal source

Certain rough sapphires processed by the high temperature technique could be identified, and there was a reason for choosing those specific goods: they are higher in iron content and prove to respond better to HPHT treatments.

“Madagascar and Sri Lanka are the preferred source for this treatment with sapphire,” Peretti says. 

Further, he notes, not all corundum responds to HPHT treatment.

“On basaltic [from dark igneous rock deposits like those sources in Nigeria, Australia, etc.], it was unsuccessful. The method seemed to add rather than reduce the colour.” 

Disclosure and transparency

Many in the trade are pushing for transparency and the enforcement of a universal system of disclosure and identification regarding HPHT-treated sapphires. This is in no way intended to quash sales, but rather to allow all actors along the pipeline (including the end users) to understand what they are dealing with. These products have a right to be offered in the marketplace—with full disclosure, of course. 

The harmonization of identification, Peretti notes, would effectively arm suppliers, dealers, and retailers with the facts needed to properly inform customers about the gemstones they wish to purchase.

“There needs to be a time period during which the stones can be thoroughly tested for hardness, brittleness, or colour stability,” he says.

Patel adamantly agrees with the need for clarity and disclosure of this relatively new process, adding it’s not enough to simply say the sapphire was ‘heated’ or ‘treated.’

A 10.64-carat HPHT-treated faceted sapphire unresponsive to traditional heating methods was treated again with heat plus pressure and re-polished.
A 10.64-carat HPHT-treated faceted sapphire unresponsive to traditional heating methods was treated again with heat plus pressure and re-polished.

“For the integrity of the trade, it is necessary to know and to pass on the information about the treatment done to the stone,” he says. “If the stones are classified [accurately], then it would be easier to differentiate between the value of an HPHT- and a conventionally heated-sapphire.”

At Byrex, Patel notes, the seemingly interchangeable use of ‘conventionally heated’ and ‘HPHT-treated’ employed by some retailers occasionally results in price confusion for customers.

“While we don’t promote or sell HPHT sapphire goods, we sometimes face tough price situations with customers where our conventionally heated sapphires become much pricier than the HPHT ones,” Patel says “With customers not knowing about [the difference in price], they assume we are selling [stones] at a more expensive price than others who do not disclose and [instead] sell HPHT as only ‘heated sapphires.’”

Patel also points out the necessity for smaller goods to be certified.

“Bigger stones of higher quality are always certified,” he says. “[Issues arise] with the smaller stones, like those under three carats, where it becomes of utmost importance to differentiate these treatments. Hence, it is most important stones treated with HPHT be separated.”

Say it like it is

Selection of large HPHT-treated sapphires, mounted in rings. Photos courtesy GRS Laboratories
Selection of large HPHT-treated sapphires, mounted in rings.

Disclosure is beneficial for the entire industry, as it helps maintain trust among trade members. Likewise, disclosure has a critical effect on consumers.

HPHT-treated sapphires produce coveted hues, and some of the stones are larger than 20 carats—indeed, impressive jewellery can be created using these goods! What’s important, however, is that everyone along the chain understands what they are buying.

Justin Opert, founder of Toronto-based Sorbet Sapphire, which specializes in the distribution of naturally coloured sapphires, perfectly understands the effect of transparency throughout our industry.

“Without full disclosure, the buyer is left uneducated and cannot make an informed decision,” he says. “Even further to that, it might cause the buyer to mistrust a retailer/wholesaler without actually having the correct information.”

Diana Jarrett is an award-winning trade journalist and graduate gemmologist (GG). A registered master valuer, Jarrett is a popular conference and trade show lecturer. She is also the co-author of Cameos Old & New (4th Edition) and the co-creator of JewelryWebsiteDesigners.com. Jarrett can be reached via e-mail at diana@dianajarrett.com or through www.dianajarrett.com.

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