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Do Lab Created Diamonds Test Positive on a Diamond Tester?

Considering a lab-grown diamond but worried it won’t past the muster if tested on a diamond tester? Fear not, you’ve come to the right place. The TLDR — lab created diamonds test positive on a diamond tester BUT there are three key ways in which they differ.


Lab diamonds are not diamond simulants

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. This is because, we’ll repeat it, they are diamonds. According to both Frank Darling and the FTC, your diamond is a diamond whether it was created in a lab or not.

Now that’s out of the way, let’s move on. 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. 

There are three physical differences between lab-created and mined diamonds. None of these differences have an effect on the integrity, optics, or beauty of the diamond. Brace yourself; this is going to get technical.


1. Their Type

Experts group natural diamonds into two main categories — 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. It accounts for up to 1% of a type Ia diamond by mass. It’s the main reason that some diamonds sport a yellow tinge.

In contrast, lab grown diamonds grow in a highly controlled nitrogen starved environment. This results in a different type of diamond — type IIa. Type IIa diamonds can occur in nature, but they’re very rare, and highly valuable. Only 5% of mined diamonds are type IIa.

A diagram illustrating the structural difference between type 2a and type 1a diamonds

2. How They Are Grown

There are two ways to grow diamonds in a lab.

HPHT, which stands for high-pressure-high-temperature, and CVD, chemical vapor deposition. Let’s talk about HPHT first.

What does HPHT stand for?

HPHT stands for high pressure high temperature. The process mimics the natural conditions that form diamonds in nature. Diamonds grow in as little as two weeks.

The drawbacks of HPHT

HPHT diamonds often exhibit a yellow or brown tinge.

HPHT diamonds sometimes contain metallic inclusions. Under magnification these inclusions look like black hairs. This is flux. It’s a magnetic relic of the growing process. While flux won’t hurt the integrity of your diamond, we recommend looking for a diamond without it.

Flux can be reflective since it’s metallic. Credit: GCAL

Flux under extremely high magnification. Credit: GCAL

What does CVD stand for?

CVD stands for chemical vapor deposition. CVD diamonds grow in a vacuum chamber pumped with methane gas. Romantic, isn’t it?

How it works

First, a technician places a diamond seed in the chamber. These seeds look like very tiny carbon wafer cookies.

Second, the chamber is pumped with methane gas.

Third, a laser or microwave beam is used to break down the gas. As the gas breaks down, carbon atoms fall onto the diamond and crystalize. Romantic isn’t it?

Finally the technician removes the diamond from the chamber and cuts away its black coating, revealing the white rough below.

The drawbacks of CVD

Similar to HPHT grown diamonds. CVD diamonds can exhibit colored tinges and is difficult to master.

CVD diamonds can also have a unique graining pattern that is visible to the eye.

A flat cloud of black inclusions seen in a CVD diamond. Credit: GCAL

A single sharp plane that appears in CVD diamonds. Credit: GCAL

What kind of diamonds can be grown with CVD?

CVD can grow white, yellow, pin-orange or even blue diamonds by introducing other gasses like boron or nitrogen into the chamber.

3. The Shape of the Rough

In nature, diamonds form over a long period under high temperatures. These two factors result in this unique octahedron shape. You might be thinking, what’s shape got to do with it? Well, while the rough diamond shape doesn’t impact a diamond’s material properties or beauty, it does change which diamond shapes is the most efficient to produce. This determines the price. It’s why princess cut diamonds are more affordable, and round brilliants are not.

Unlike mined diamonds, lab created diamonds grow over a short period under lower heat.

Again, unlike mined diamonds, lab created CVD diamonds grow upwards into a cube.  Lab created HPHT diamonds grow into a cube-octahedron hybrid shape. This makes lab diamonds better suited to square shapes like the cushion, rather than elongated or flat shapes like the marquise or trillion. The rule of thumb? Inefficient = expensive.

A diagram showing the different crystal formations lab grown HPHP, CVD and mined diamonds grown in used to illustrate why diamonds test positive on a diamond tester

Like tree’s, diamonds have layers that indicate their growth pattern. With the right equipment, under extremely high magnification, you tell you whether a diamond originally grew into a cube, octahedron or cube-octahedron hybrid. Under super magnification in a lab, or using photoluminescence spectroscopy, it is possible for a trained gemologist to tell a lab diamonds apart from a mined diamond, by examining the growth pattern.


Yes — but, there are three ways lab diamonds differ from mined diamonds.

1. Their type

Identifying a diamond as type Ia proves that is is mined. Identifying a diamond as type IIa does not prove that it is lab grown.

2. How the are grown

Under magnification, a diamonds growth pattern can indicate if it was mined, grown using CVD or grown using HPHT. In addition, certain diamonds have physical indicators that are relics of the growth process.

The presence of flux

Flux is only present in HPHT grown diamonds. Lab created diamonds rarely exhibit fluorescence.

The presence of fluorescence

Mined diamonds exhibit fluorescence about 30% of the time. Click here to learn more about diamond fluorescence and why it matters.

3. The shape of the rough

Lab diamonds grown into cubes. Mined diamonds grown into octahedrons.


Frank Darling offers offers one of the largest selections of lab grown diamonds online, with more than 10,000 IGI and GCAL certified diamonds available in 360 degree video. All diamonds come with 30 day free returns, financing starting at 0%, and a price match guarantee.