CVD vs. HPHT: How Are Lab-Grown Diamonds Made?

A diamond that took a billion years to form in nature can now be grown in a matter of weeks — and it's chemically, structurally, and physically identical to a mined diamond. That's the reality of lab-grown diamonds today.

But how exactly do you compress a billion years of geology into a lab process? There are two methods: HPHT (High Pressure High Temperature) and CVD (Chemical Vapor Deposition). Both produce real diamonds — just through very different processes. And that’s where things get interesting.

A Brief History of Lab-Grown Diamonds

Scientists have tried to grow diamonds in a lab for more than a century. The first real breakthrough came in the mid-1950s, when researchers recreated the extreme pressure and heat that diamonds naturally form under. This became HPHT — the first method that could reliably make diamonds, though mostly for industrial tools like cutting and drilling, not jewelry.

CVD research started around the same time, but it took longer to work well. It wasn't until the 1980s that CVD could reliably produce diamonds good enough, and big enough, for jewelry. From the 1990s onward, both methods kept improving. Today, CVD and HPHT are both trusted, established ways to grow gem-quality diamonds.

HPHT: Growing Diamonds With Pressure and Heat

HPHT recreates the conditions found deep inside the Earth, where natural diamonds actually form. A small diamond seed sits inside a growth cell along with a carbon source — usually graphite — and a metal material called a flux. The whole cell is squeezed under roughly 5–6 gigapascals of pressure and heated to about 1,300–1,600°C.

That heat melts the flux, and carbon dissolves into it. As the carbon-rich liquid reaches the cooler seed, carbon atoms crystallize onto it and slowly build up a diamond. Depending on the size, this can take anywhere from about an hour to several weeks.

The crystals that come out of this process have their own distinct growth patterns — different from both natural diamonds and CVD diamonds. That's exactly what lets gem labs tell how a diamond was made.

HPHT production site

HPHT And The Size Of Diamonds

HPHT has traditionally been especially good at making smaller diamonds, including the tiny "melee" stones used in pavé settings. That's a big reason HPHT plays such a large role in diamond production overall. But don't think of one carat diamond as some kind of ceiling for HPHT. The technology has come a long way — GIA has recorded HPHT crystals over 100 carats, including a 150.42-carat crystal grown in 2021.

So the real difference between HPHT and CVD isn't a strict size limit. It's rather a size distribution: HPHT has historically been efficient for smaller stones, while CVD has become the go-to method for larger, gem-quality diamonds.

CVD: Growing Diamonds Layer by Layer

CVD works in a completely different way. Instead of huge pressure, it happens inside a vacuum chamber at much lower pressure. Flat diamond seeds sit inside, exposed to a carbon-rich gas — usually a mix of methane and hydrogen.

Microwaves create a plasma inside the chamber. This breaks the gas apart, releasing carbon atoms that settle onto the seed and crystallize — building the diamond one layer at a time. This happens at lower temperatures than HPHT, around 900–1,200°C, and it usually takes several weeks.

The CVD rough crystal that emerges is usually flat, like a plate — unlike the compact, three-dimensional crystals produced by HPHT.

CVD production site

Why CVD Is Linked to Larger Diamonds

Early CVD diamonds were small, and not really suitable for jewelry — even through the early 2000s, gem-quality CVD stones were still pretty limited. That's changed a lot since then. According to GIA, most CVD diamonds submitted for grading before 2010 weighed less than half a carat. Today, most exceed 3 carats, and stones of 10 carats or more are becoming increasingly common.

That doesn't mean CVD is only for large stones — smaller CVD diamonds are still produced all the time. It just means CVD has become especially good at producing larger, gem-quality diamonds, which is why manufacturers often choose it for larger center stones.

CVD vs. HPHT at a Glance

Neither method is "better." They're just two different ways to grow the same material.

Where Lab-Grown Diamonds Are Actually Made

China has long been the biggest producer of lab-grown diamonds by volume, and it's closely tied to HPHT. Chinese manufacturers make large amounts of smaller stones, including melee-sized goods, along with a good amount of CVD production too.

India, especially the city of Surat in Gujarat, has become a major center for CVD. Surat was already one of the world's biggest diamond cutting and polishing hubs, and it has built up huge CVD manufacturing capacity.

The United States also has a long history in CVD research and production, and both methods are used in other countries too.

HPHT: Growth Method or Treatment?

Here's one detail worth knowing: HPHT can refer to two different things. It can describe the growth method outlined above, or it can refer to a treatment applied after a diamond has already been grown. In fact, a diamond can be grown with CVD, then treated with HPHT afterward.

Why would that happen? Some CVD diamonds come out slightly brown. A controlled high-heat treatment can change the diamond's structure and improve its color, sometimes making it fully colorless. That's why you might see a diamond described as "CVD-grown, HPHT-treated" - a nod to these two separate steps: how it was grown, and how its color was improved afterward.

Does the Growth Method Affect Quality?

Not really. Both CVD and HPHT can produce excellent, gem-quality diamonds. The growth method alone doesn't decide whether a diamond turns out beautiful or jewelry-worthy.

Like any diamond, the finished stone is graded by the 4Cs: color, clarity, cut, and carat weight. What matters most is transparency. A lab-grown diamond should always be clearly labeled as such.

The Bottom Line

CVD and HPHT take very different paths to the same result. One builds a crystal slowly, layer by layer, from a carbon-rich gas. The other uses intense pressure and heat to recreate what happens deep inside the Earth.

No matter which method a diamond started with, its carbon atoms end up forming the exact same crystal structure — the one that gives diamond its hardness, brilliance, and everything else that makes it diamond.

Lab-grown Diamonds at amadia - young diamonds

At amadia, we use both CVD and HPHT diamonds. As you now know, neither method is better than the other — they're just two different ways to grow the same real diamond. What matters to us is quality.

That's why every diamond in our jewelry is D-F color, meaning completely colorless, and VS1 clarity or higher, meaning eye-clean brilliance with no visible flaws. Whether a stone was grown with CVD or HPHT, this is the standard we hold it to before it ever makes it into one of our pieces.

Ready to see it for yourself? Enjoy our lab-grown diamond collection:

bracelets — earrings — necklaces — pendants — rings

Frequently Asked Questions