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Diamond Detection

Tips for investing in synthetic diamond screening technology

By Shawna Kulpa

Manmade diamonds aren’t going anywhere. As the technology to grow them has advanced, so too has their presence in the marketplace: It’s been estimated that at least 25 percent of independent jewelers now carry them, and their appeal among consumers is growing. Some jewelers believe they’ll remain a niche product; others envision them overtaking the popularity of natural diamonds. One thing is certain, though: If you work with diamonds, you will eventually come into contact with one that’s been grown in a lab.

What isn’t certain is, will you be able to tell?

Unfortunately, to the frustration of many, there is not yet a magic black box that can identify every stone, every time. “It’s a complex subject matter,” says Harold Dupuy, FGA, vice president, strategic analysis, at Stuller Inc. in Lafayette, Louisiana. “Most people are looking for a simple answer.”

It may not be simple, but it is important—especially since, as Dupuy notes, contamination exists in the marketplace, particularly with melee. Whether you’re a manufacturer, a designer, or a retailer, whenever you sell a diamond, you’re putting your faith and reputation on the line. It’s critical that you buy the best diamond-screening device to meet your needs. So how do you do that?

By asking questions—starting with what test methods are used and how they operate.

Testing Methods

Before investing in a device to detect whether or not a diamond could be lab-grown, it’s important to have a basic understanding of the testing methods used by the devices currently on the market.

Many of these devices are testing to determine whether the diamond is a Type I or Type II. Type I diamonds ac-count for approximately 98 percent of all natural diamonds and contain nitrogen impurities. “If a machine tells you that [a colorless stone] is a Type I, at the present time, you don’t need to do any further testing,” says Stanley Zale, vice president of diamonds and gemstones at Stuller Inc.

Type II diamonds, on the other hand, contain no measurable nitrogen impurities. All colorless lab-grown diamonds, no matter how they’re created, lack nitrogen and are classified as Type IIa. (Type IIb diamonds share the same lack of nitrogen as Type IIa, but also contain boron impurities.) Screening for nitrogen is one of the ways that testing devices use to quickly identify any diamonds that could be manmade.

However, testing as a Type II is not a guarantee that a stone is manmade, as Type II stones account for about 2 percent of natural diamonds. “What’s ironic,” says Zale, “is that the greatest diamonds in the world that occur naturally are Type II. The Cullinan Diamond is a Type II.”

According to Dr. James Shigley, a distinguished research fellow at GIA in Carlsbad, California, there are four basic methods used to detect if a diamond is natural or manmade. With the simplest method, diamonds can be tested for their transparency to ultraviolet (UV) light.

“Most natural diamonds are not transparent to ultraviolet light, whereas colorless synthetic diamonds are transparent,” explains Shigley. If a diamond being tested is opaque to UV light, it should register as a natural stone.

The second method examines the visible and ultraviolet spectrum of a diamond, as there are particular parts of the spectrum that a natural diamond will absorb. “Most natural diamonds are yellowish due to the presence of nitrogen, which is distinctive in the ultraviolet spectrum, but the spectral features due to nitrogen are lacking in synthetic diamonds,” Shigley says.

Another method uses spectrum-based fluorescence detection. The device uses a spectrometer to analyze the stone for several things, including the presence of nitrogen.

These three methods are suitable for screening synthetic diamonds created using either high-pressure, high-temperature (HPHT) or chemical vapor deposition (CVD) techniques. (See “How Diamonds Are Grown,” for an overview of each technique.) The fourth method, which examines the phosphorescence of a diamond under ultraviolet light, is best suited for testing HPHT-grown stones. Whereas the other methods are looking for characteristics found only in natural diamonds (such as nitrogen), phosphorescence screeners are looking for something found in nearly all colorless lab-grown diamonds: phosphorescence. The stone is illuminated with UV light and then measured after the light is turned off to see if the diamond continues to glow. If it does, the diamond could be synthetic, as manmade stones are typically more phosphorescent than natural diamonds. It’s best geared for testing HPHT-created stones since a small percentage of CVD-created stones may not phosphoresce enough to be picked up by the device.


Regardless of the testing method a de-vice uses, it’s important to remember that “no instrument is 100 percent accurate,” says Donald Palmieri, president of Gem Certification and Assurance Lab (GCAL) in New York City.

Most of the machines on the market issue a “pass” or “refer” ruling when screening stones. A “pass” indicates that the stone is natural, and users should have absolute confidence in those results. However, “refer” simply means that the stone may or may not be lab-grown. Stones that are flagged as “referred” should then be sent to a gem laboratory, which can conduct far more extensive testing to determine whether or not a stone is lab-grown. Users need to be aware that the possibility of a machine flagging a natural diamond as potentially lab-grown exists, as some stones have such high purity that they lack any trace of the signs these machines are screening for.


Before You Buy

Before you start asking manufacturers questions about their screening devices, you first need to identify your needs. Are you going to use the device primarily to test mounted stones, loose stones, or both? What size stones will you be testing? While a jewelry manufacturer might be primarily concerned with testing melee parcels, a diamond cutter may want to test only rough diamond material. What you intend to test will influence the type of device you should consider.

“Not all devices have the same specifications,” says David Bouffard, vice president, corporate affairs for Signet Jewelers in Akron, Ohio. “Some are designed to test single stones, multiple stones, or stones mounted in jewelry. Some will screen colored and colorless stones, and some will screen fancy shapes as well as rounds. So when a company is seeking to buy detection technology, it is very important that they specify the type of diamonds they need to test, and whether the quantities they deal with require automated equipment.”

Once you’ve identified your primary needs, it’s time to start contacting the manufacturers. The first and most important question to ask any manufacturer is about how its machine actually works.

“You should know what it’s doing and how it works so you can explain the instrument to your customers,” says Shigley. Being able to detail how the device determines if a diamond is manmade or natural is a great selling feature for customers, both retail and wholesale alike. It assures them that you are up on the latest developments in the field and that you’re taking the necessary steps to ensure that you know what you are selling.

In addition to asking how the instrument works and what it can do, it’s also critical to ask what it can’t do, advises Dupuy. For example, depending on what type and size of diamonds you’ll be testing, you may want a machine designed to test for both HPHT and CVD stones, rather than the phosphorescence testers that are best used for detecting HPHT-grown diamonds. Alternatively, if you’re primarily concerned with testing melee, an HPHT-only detector may be suitable since most melee is HPHT created.

Once you have a clear understanding of how the devices work, it’s time to delve into the nitty-gritty details.

Can it be used to test mounted or loose stones, or can it test both? 

If your primary concern is testing loose melee, you may be happy with a machine that’s designed to test only loose stones. However, if you have plans to test both loose and mounted stones, make sure any device you consider offers that function. Also, if you’ll be testing mounted stones, ask if the device can test mounted stones that might not be open in the back, as some methods rely on the ability to pass light through a stone.

What is the capacity of the device?

If you’re primarily interested in testing the occasional diamond—a stone in a piece that came in for repair, for instance, or that you received for a client’s custom piece—you may be happy with a handheld device designed to test one stone at a time. However, if you want to test lots of set or loose stones quickly, you would want a device capable of testing multiple stones simultaneously. Some models have trays that can hold thousands of melee stones or dozens of diamond-studded jewelry pieces that can all be tested at the same time.

How do I interpret the screening results?

Ask what the test results mean, and what you should do with them. Most machines don’t provide a clear-cut “yes” or “no” answer to whether a stone is manmade or not. Instead, most machines will issue a “pass” for natural stones and a “refer” for stones that aren’t identified as natural. Those “referred” stones should then be sent to a gem lab for more definitive testing. If a device issues another type of reading, such as “synthetic,” “CVD,” or “HPHT,” users should still plan to send those stones out for further testing, since false readings of natural stones are possible.

What is the accuracy of the device?

While no machine currently offers 100 percent accuracy, it’s still important to ask about the degree of accuracy and how that figure has been determined. “What testing did the vendor do to validate this instrument?” asks Shigley. “Did they test 10,000 diamonds? What did they do to demonstrate that it works correctly? The more diamonds they’ve tested, the better. The more testing that has been done, the greater confidence you can have.”

And don’t just take the vendor’s word on how the machine has been tested. Shigley recommends asking if they have any published documentation that will back up their test result claims.

(“There is a project to design a standard for diamond detection technology, under the auspices of the Diamond Producers Association,” says Bouffard. “The standard is being developed by Underwriters Laboratories, an independent, global safety consulting and certification company, which specializes in product testing. Once this standard is available, manufacturers of detection equipment will be able to have their devices tested and the results published. This will provide an independent reference for anyone wishing to buy detection technology.” He expects the standard guidelines to be available later this year.)

What is the warranty on the machine and what kind of support does the vendor provide?

Finally, don’t forget to ask about the warranty and the level of support the manufacturer offers on its device.

“You want someone with longevity who’s going to be around to service the machine as time goes by,” says David Skuza, North American agent for DRC Techno in Surat, India. “And ask about the warranty. This is cutting-edge technology. You have to be well supported and know what will happen if something fails.”

Although there is no single machine that can do it all, the technology is constantly changing and it’s important to stay on top of developments in the field. Lab-grown diamond manufacturers are constantly working on their recipes to create a more perfect, more colorless diamond. As those recipes change, it’s likely the machinery needed to detect them will need to change too. “Read the trade magazines to find out when something really new hits the market,” advises Palmieri. “Get the basic technology and stay abreast of what’s happening with the industry.”


Diamond Screening Devices


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