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What Makes a Good Synthetics Detector?

Mar 12, 2019 7:12 AM   By Joshua Freedman
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The massive project by the Diamond Producers Association (DPA) and Signet Jewelers to test and review 18 synthetic-diamond detectors has raised an important question: What should you look for in such a machine?

Accuracy is, of course, a major part of the equation (alongside speed, price and usability), but it isn’t a clear-cut issue. The first set of results from the DPA and Signet’s Assure Program, which came out last week, gave up to nine different performance scores for each scanner, reflecting their varied abilities.

The criteria don’t all apply to every machine, as only five of them can conclusively detect lab-grown diamonds, while six merely claim to refer questionable stones for further checks. The other seven are still undergoing testing.

Definitely natural

The DPA believes the most important factor is the ability to verify that a diamond is natural, rather than being able to say that a stone is definitely synthetic or definitely a simulant. It calls this key metric the “diamond false-positive rate.” The good news is that all but two devices scored 0%, indicating they didn’t mistakenly label any man-made stones as natural. (See the list at the end of this article.)

“It’s a reflection of the instrument’s ability to ensure that only natural diamonds are verified as natural diamonds,” said Jean-Marc Lieberherr, CEO of the DPA. “From a consumer perspective, this is the primary function of a diamond-verification instrument.”

Consumers expect retailers to give formal reassurances that their products are what they say they are, and those are only as reliable as the detection machines the retailer or supplier used, Lieberherr explained. Out of all the associated risks, the main one is that a synthetic diamond should mistakenly be sold as natural, he added.

Refer: A friend?

That measure is far from the only important one. A machine that’s overly strict, wrongly referring some natural diamonds for further testing, might be good if you want to be sure you’re left with only natural stones. But those additional tests may be expensive. You might need to buy more than one machine. Plus, a buyer who receives a batch of natural diamonds and finds that some of them can’t be verified may grow unnecessarily suspicious of his or her supplier.

That’s why some traders may also look at the “diamond referral rate,” which is the percentage of natural stones that a machine categorizes as undetermined (“refer”). Again, 0% is the best, with only one instrument — De Beers’ DiamondView — achieving that. Some machines didn’t get a score, as they don’t classify stones as “refer.”

Looking for lab-grown?

But what if you’re a synthetics company looking to ensure your inventory comprises entirely lab-grown diamonds? The relevant measure might be the “synthetic-diamond false-positive rate,” which assesses how often machines wrongly labeled stones as lab-grown, when they were in fact natural diamonds or simulants.

“The relative importance of the other metrics is up to the individual device buyer, as there may be different motivations,” Lieberherr noted. “For example, some synthetic-diamond dealers may want to pull out all the synthetics, and would care less about the referral rate.”

Sure thing

Other measures give an idea of machines’ more categorical findings. Only a few were perfect at identifying natural or synthetic diamonds conclusively. DiamondView was the only one that correctly spotted all the natural diamonds, without mislabeling or referring any of them. The De Beers machine was also one of only two that categorically identified all the lab-growns, the other being the Sherlock Holmes from Yehuda. (Presidium’s Synthetic Diamond Screener II didn’t get a score for that measure because it only refers stones, though the Assure Program’s initial report wrongly gave it 100%, a DPA spokesperson confirmed. Rapaport News has corrected an earlier story to reflect this.)

However, most people who buy synthetics detectors are mainly interested in being sure that the stones they think are natural are indeed so. By that measure, most of the devices gave a good showing.

How the testing worksThe Assure Program tested 18 machines from 11 manufacturers against a standard developed by UL, a third-party testing agency, and by a technical committee of gemologists.

Some of the committee members were from device manufacturers, including De Beers, the Gemological Institute of America (GIA), and the Antwerp-based Scientific and Technical Research Center for Diamond (WTOCD), which developed the M-Screen+ machine that HRD Antwerp sells. For that reason, an independent adviser supervised the creation of that standard to ensure impartiality, Lieberherr noted. All committee members approved the standard and the sample of stones, and UL carried out the tests independently, he added.

The sample comprised 1,000 natural diamonds and 200 synthetics, including stones created by chemical vapor deposition (CVD) and High Pressure-High Temperature (HPHT), while some of the man-made specimens had undergone post-growth treatments. All were round brilliant cuts, larger than 2 millimeters in girdle diameter, D to J color, and of mixed clarity. Machines that claim to detect simulants such as cubic zirconia also underwent testing on a sample of 200 of those.

The batch was intentionally challenging, and included custom-made synthetics that are not yet available commercially. That ensured the test was “future-proof” and able to differentiate effectively between the instruments, the DPA explained.

The DPA initially tested each stone with several gemological laboratories to confirm their origins. The natural and lab-grown diamonds also had slightly different sizes, enabling UL to verify machines’ answers using sieves.

“This system, proposed by the technical committee, has proven to be 100% reliable,” Lieberherr said.

The DPA will release results of further tests in the coming months, covering new samples with additional sizes and colors, as well as stones mounted in jewelry.

Machines that scored full marks:

Diamond false-positive rate of 0%:
(the percentage of synthetic diamonds or simulants wrongly classified as natural)
AMS2 (manufactured by De Beers)
DiamondDect 3 (Taidiam Technology)
DiamondSure (De Beers)
DiamondView (De Beers)
GIA iD100 (GIA)
M-Screen+ (HRD Antwerp)
Sherlock Holmes (Yehuda)
SYNTHdetect (De Beers)
Synthetic Diamond Screener II (Presidium)

Diamond referral rate of 0%:
(the percentage of natural diamonds referred for further testing)
DiamondView (De Beers)

Diamond accuracy rate of 100%:
(the percentage of natural diamonds correctly categorized as natural)
DiamondView (De Beers)

Image: Taidiam Technology’s DiamondDect 5 — one of 18 machines undergoing testing under the Assure Program. (DPA)
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Tags: AMS2, Assure Program, De Beers, Diamond Producers Association, DiamondDect 3, diamondsure, DiamondView, Dpa, GIA, GIA iD100, HRD Antwerp, Jean-Marc Lieberherr, Joshua Freedman, M-Screen+, Sherlock Holmes, Signet, Signet Jewelers, SYNTHdetect, Synthetic Diamond Screener II, Synthetics, Taidiam Technology, Yehuda
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