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CVD Diamonds — as Good as HPHT Diamonds?

All the diamond acronyms driving you crazy? Learn the difference between CVD diamonds and HPHT lab grown diamonds and which one you should buy. 

By Stephanie Dore

Way Back, Back into Time 

It takes millions, no, billions of years for the Earth to form a natural diamond. In fact, many date back farther than the oldest plants! And they go through a lot to make it onto your pretty little finger. Not to mention their often tabloid-worthy history and endlessly fascinating properties. So fascinating, really, that humans have long tried to replicate their brilliance. But it hasn’t been until the last century that lab grown diamonds (also referred to as CVD diamonds) have gotten anywhere near their natural competition. 

Today, despite the growing popularity of lab grown diamonds, when it comes to laying down some cold hard cash for one, there’s still plenty of confusion. This includes whether they are a simulant or a synthetic (they’re synthetic btw—while both are produced in a lab, synthetic diamonds have the same chemical, physical, and optical properties as natural diamonds; simulants do not), whether they look the same as a natural diamond (they do!), and just how they’re made—we’re about to get to that. But once you’ve waded through all that noise and realized they’re actually the same as natural diamonds, you’re faced with another fork in the road. 

CVD diamonds vs. HPHT diamonds. Wait, what? 

The OG of Lab Grown Diamonds

The original process used to create lab grown diamonds, high pressure high temperature (HPHT) mimics the natural growing conditions of diamonds that come from deep within the Earth’s crust. It’s a bit like making ice if the analogy helps: Ice forms naturally, yet you can reproduce the same conditions from the comfort of home to make it yourself. Much like diamonds. Just don’t try this at home.

The first reproducible lab grown diamond was created using HPHT in 1954. The process uses a press to generate pressure over 1.5 million pounds per square inch and heat above 2,000 degrees Celsius to grow a diamond from a small seed. And once that diamond is grown, it’s sent off to be cut and polished just like a naturally-grown diamond. HPHT is known for producing large, white diamonds in the 2-5 carat range with D-F color. It is also used to treat both natural and CVD-grown diamonds to make them whiter. 

CVD Diamonds — The New Kid on the Block

CVD on the other hand—which stands for chemical vapor deposition—is the modern disruptor of lab grown diamond technology. With CVD, a thin slice of diamond seed (often produced through HPHT) is placed in a sealed chamber and heated to around 800 degrees Celsius. The chamber is then filled with a carbon-rich gas (usually methane) along with other gases. 

The gasses are then ionized into plasma using microwaves, lasers, or other techniques, which breaks down the molecular bonds in the gases and causes the pure carbon to adhere to the diamond seed. What then? Well that carbon slowly builds up into a larger diamond crystal, atom by atom, layer by layer. CVD tends to grow smaller, warmer-toned diamonds in the 1-2.5 carat range with G-I color.

But are They Real?

We know. All you really care about is whether CVD or HPHT diamonds are really, well, real. And yes. They are. Both of these processes produce gem-quality diamonds physically, chemically, and optically identical to natural diamonds. They’re the same thing. Just like ice grown in your own freezer is still ice. 

How Can You tell if it’s a CVD diamond or HPHT?

Well, assuming you’ve purchased it from a reputable source, the growing process will be listed on the diamond certificate. But there are few other ways to deduce its origin if you want to test your detective skills. Remember, if it’s a D-F color diamond over 2 carats, it’s most likely HPHT, while CVD tend to be smaller and warmer colored. Some HPHT diamonds are also magnetic! This happens when metallic flux (a remnant of the growing process) is present inside the diamond. They may also have a slight “blue nuance” listed on their certificate, which is caused by the presence of boron gas in the growing chamber. CVD diamonds on the other hand, may have silicon inclusions, (remnants of their growing process) that are not present in natural diamonds. 

An illustration showing how CVD diamonds are grown
A CVD diamond after it
has been grown and cored
Moissanite – note the fire

What about Moissanite? How do I Know the Difference?

As if there weren’t enough curve balls here, there’s a gem called Moissanite, a man-made diamond simulant, that’s all up in the mix. And sometimes, HPHT lab grown diamonds will test positive as Moissanite on a Moissanite tester (a little pen-shaped tool that gives a quick readout of a stone’s electrical conductivity). This is because some HPHT diamonds may have boron in their structure, which makes them electrically conductive like Moissanite. Regardless, a reputable jeweler should be able to help you determine the difference.

Just your Type

Because we want you to be able to decipher all the terminology, you should know that diamonds are classified in five different types—referring to their atomic structure—known as Type Ia, Type Ib,Type 1aB ,Type IIa, and Type IIb. Type I diamonds make up most of the natural diamonds you’ll find on the market, while it’s rare to find a Type II. But HPHT diamonds are more likely to be Type IIb due to their boron impurities.

As Real as Real Can Be

When it comes to whether you should buy an HPHT or CVD lab grown diamond, both are great options. They each have the same atomic, physical, and optical properties of natural diamonds and will display the same brilliance, fire, and scintillation (aka sparkle) when skillfully cut.