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Do Lab-Created Diamonds Test Positive on a Diamond Tester?

So you’re considering buying a lab-grown diamond and worried it won’t past the muster if tested on a diamond tester? Fear not, brave soldier. While some jewelers might refer to lab-created diamonds as imitations or simulants, this is incorrect.

Cubic zirconia and moissanite are simulants – lab-grown diamonds, are, as the name suggests, diamonds. They have the same chemical, physical, and optical properties as mined diamonds much to the mining industry’s chagrin. Unlike diamond simulants such as CZ or Moissanite, lab-created diamonds will test positive when using a diamond tester because we’ll repeat it, they are diamonds. Rest assured that according to both Frank Darling and the FTC your diamond is a diamond whether it was created in a lab or not.

Now that we’ve gotten that out of the way — from time to time a salesperson on the internet will claim to be able to tell the difference between a mined diamond and a lab-created diamond while providing limited details on how they achieve such a miraculous feat. 

To set the record straight, we’re going to break down the only three real physical differences between a lab-created diamond and a mined diamond. While none of these traits have an effect on the integrity, optics, or beauty of the diamond — they’re important to know about. There’s a lot of misinformation out there and if you’re like us, you like to get to the bottom of things. Brace yourself; this is going to get technical.


Natural diamonds can be grouped into two main categories, called type Ia and type IIa

Type Ia diamonds contain nitrogen; type IIa diamonds don’t.  

Fun fact, nitrogen is the most common impurity in diamond, making up to 1% of a type Ia diamond by mass. It’s the main reason that some diamonds are slightly yellow tinged, and the reason we have color grades.

All lab-grown diamonds are type IIa — meaning they contain no nitrogen. This is because they are grown in a highly controlled and nitrogen starved environment. Type IIa diamonds also occur in nature, but they’re very rare, and highly valuable. Only 5% of mined diamonds are type IIa.

A diamond that is identified as type IIa is not necessarily a lab diamond. But based on how rare diamonds of this purity are found in nature, the odds are somewhat more likely.


Lab-created diamonds are grown via two processes, HPHT, high-pressure-high-temperature, and CVD, chemical vapor deposition. A combination of both is also used. Let’s talk about HPHT first.

HPHT stands for high pressure high temperature, mimicing the natural conditions that form diamonds. HPHT diamonds are grown in small capsules for as little as two weeks to a month or more. They can exhibit yellow or brown tinges, which makes the diamonds that result from this process better suited for industrial use. Occasionally they can contain metallic inclusions due to the presence of flux in the growing process. The best way to identify them is via photoluminescence spectroscopy, which can highlight irregularities in the color distribution, fluorescence, and graining.

CVD stands for chemical vapor deposition. CVD diamonds grow in a vacuum chamber pumped with methane gas. Romantic, isn’t it? A thin wafer of diamond, called a seed, is placed in the chamber, and a laser or microwave beam breaks down the gas. As the gas is broken down, carbon atoms gently fall onto the diamond seed and crystalize, like falling snow, romantic after all. In some cases CVD diamonds can exhibit a brown or grey tint, but they can also be bright white, or grown in fancy colors like yellow, pink-orange and blue by introducing boron or nitrogen into the chamber.

CVD diamonds grow in the shape of a cube. After they’re cut, you’d never know what their original shape looked like, but with incredibly powerful magnification, it is possible to observe. Think of a tree’s growth rings. Diamonds have similar traces of growth that are nearly invisible, but if you have the right equipment, their shape can tell you whether a diamond originally grew in a cubic shape, or the octahedron shape of most mined diamonds.

But, to go back to our first question, both the HPHT and CVD processes produce gem-quality diamonds which test positive for diamond and exhibit identical atomic structures to the diamonds found in nature.


Natural diamonds form over a long period under high temperatures into octahedral crystals. These two factors result in this unique crystal shape and the previously mentioned presence of nitrogen and other impurities. 

Lab created diamonds are grown over a short period under lower heat than those found underground. Because of this, lab-created CVD diamonds grow upwards into a cube,  and HPHT created diamonds grow into a cube-octohedron hybrid shape. 

Crystal formation in diamond showing the natural diamond crystal shape vs the HPHT diamond crystal shape and the lab grown diamond crystal shape.

While the rough diamond shape doesn’t impact a cut and polished diamond’s material properties or beauty, it does change which diamond shapes are most efficient to produce. Most natural diamond rough pieces are well shaped for cutting into round diamonds, whereas CVD rough is better suited to square shapes like the cushion, rather elongated shapes like the marquise. CVD rough is also well suited for rounds, and nearly all shapes are available in CVD, but their pricing depends primarily on how efficiently they fit into the cubic rough shape.

So to recap. Lab created diamonds do test positive on a diamond tester, but viewed under super magnification in a lab or using photoluminescence spectroscopy, it is possible for a trained gemologist to tell them apart by examining their growing pattern. Identifying a diamond as type Ia could prove that it is a mined diamond, but identifying it as type IIa is not enough to prove that it is lab grown.

Since not every lab-created diamond will have all or any of these characteristics it is very difficult to know with 100% certainty if a diamond was lab-created or mined. Regardless, none of these factors affect how the diamond looks or tests with a diamond tester.

Not convinced? Read up on the myths behind lab-grown diamonds.


Every great ring starts with a great setting, but picking a setting out online is hard — or at least it used to be. At Frank Darling, all our engagement ring settings are available for free home try-on. It’s like the internet, but you can touch things.

Get started by selecting your favorite four rings. We’ll send you sterling silver size seven replicas set with 1 carat CZ stones. Want to see other stone sizes? Just ask.

Each try at home kit comes with a pre-paid return label, ring sizer, and The Handbook. A practical guide to purchasing a diamond for the matrimonial inclined. So, what are you waiting for? Let’s get this party started.