CVD vs HPHT Lab Diamonds: Technical Comparison

CVD and HPHT are the two methods used to grow diamonds in a lab, and both produce a genuine diamond with the same crystal structure, hardness and chemical makeup as a mined stone. The two processes differ in equipment and growing environment, and each tends to leave its own faint fingerprints that a gemologist can spot under magnification — but neither method makes for a “better” diamond on its own. What actually determines how a lab-grown diamond looks and performs is the finished stone’s own cut, color, clarity and carat weight, not which process grew it.

How lab-grown diamonds are made, in brief

Both CVD and HPHT start from a thin diamond “seed” and build carbon onto it, atom by atom, until a rough diamond crystal has formed. That rough stone is then cut and polished exactly as a mined diamond would be. Because the resulting crystal is carbon arranged in the same cubic lattice as a natural diamond, a lab-grown stone shares the same hardness — 10 on the Mohs scale — the same optical properties, and the same chemical composition. The difference between the two is entirely in how and where the growth happened, not in what the finished diamond is made of. For a fuller overview of lab-grown diamonds generally, see our complete guide to lab-grown diamonds.

The HPHT process

High Pressure High Temperature (HPHT) growth recreates, in a controlled chamber, something close to the conditions under which diamonds form naturally deep underground. A diamond seed is placed with a carbon source inside a press and exposed to very high temperature and pressure — commonly cited as roughly 1,300–1,600°C and several gigapascals of pressure, figures that vary somewhat by equipment and are best treated as approximate. Under these conditions, carbon dissolves and re-crystallizes onto the seed, and a rough diamond forms over a period of days to a few weeks.

Typical HPHT traits

These are general tendencies seen across HPHT-grown stones, not fixed rules — any individual diamond can vary:

• Often shows a cuboctahedral (multi-faceted) internal growth pattern, visible only under magnification before cutting
• May need further post-growth HPHT treatment to lighten color in some stones
• Can contain tiny metallic inclusions left over from the growth process, which a gemologist can usually identify under magnification
• Historically associated with efficiently growing larger rough stones

The CVD process

Chemical Vapor Deposition (CVD) takes a different path. A thin diamond seed plate is placed in a sealed chamber filled with a carbon-rich gas, typically methane. The gas is heated until it forms a plasma, which breaks apart the carbon-bearing molecules and lets carbon atoms settle onto the seed one layer at a time. Growing a diamond this way is commonly described as taking a few weeks, depending on the size of stone being grown.

Typical CVD traits

• Builds up in layers, leaving a different internal growth pattern than HPHT stones
• Post-growth treatment (additional heat or pressure processing) is common for some CVD stones, generally used to improve color or relieve internal strain
• Can show faint “strain lines” under specialized lab equipment; these are not visible to the naked eye
• Well suited to growing thin, high-clarity rough

Does the growth method affect quality?

Not directly. Both methods can produce lab-grown diamonds across the full range of the 4Cs — cut, color, clarity and carat weight — and a grading lab assesses the finished stone in front of it, not how that stone came to exist. As a general tendency, CVD rough is often described as naturally trending toward higher color grades, while HPHT stones more often need treatment to reach the same range; inclusion types also tend to differ, with metallic flecks more associated with HPHT and strain patterns with CVD. Neither tendency makes one method’s output inherently worse — the individual stone’s grade, not its growth method, is what determines how it looks and wears.

How the growth method appears on a grading report

When a lab-grown diamond is submitted to a grading laboratory such as GIA or IGI, the resulting report will state that the stone is laboratory-grown and will often note the growth method — CVD or HPHT — along with whether any post-growth treatment was detected. This sits alongside the standard 4Cs assessment that any diamond, mined or lab-grown, receives. For a closer look at what else a grading report covers and how GIA and IGI compare, see our companion piece on diamond grading standards.

Does it matter when you’re buying?

For most buyers, not on its own. A well-cut CVD diamond and a well-cut HPHT diamond can look identical to the naked eye and wear identically once set. What actually affects how a stone looks and holds up is its cut quality, clarity grade and color grade, along with the setting it’s mounted in. Lab-grown diamonds are commonly set in gold, platinum or silver; GemsGlitz pieces use 925 sterling silver with a rhodium finish rather than a precious metal, which is part of how our finished jewelry stays in the $99–$189 range — see our materials page for details. If you’re comparing stones, the 4Cs and the grading report are a far more useful yardstick than the growth method.

A note on GemsGlitz stones

We don’t list the growth method — CVD or HPHT — for individual stones in our pieces. Our lab-grown diamonds are selected for their finished appearance and quality rather than marketed by production process, and, as with the rest of our range, they are not sold with an individual grading report. If a specific growth method or a matching certificate is something you need for a particular purchase, it’s worth asking any retailer directly what documentation, if any, comes with the stone.

Frequently asked questions

Is a CVD diamond “better” than an HPHT diamond?

Neither is inherently better. Both are genuine lab-grown diamonds, and quality depends on the individual stone’s cut, color, clarity and carat weight rather than on the process used to grow it.

Can you tell CVD and HPHT diamonds apart by eye?

No. Differences such as growth pattern, inclusion type and strain lines are typically visible only to a gemologist using specialized magnification, not to the naked eye.

Is a treated lab-grown diamond less valuable or less “real”?

No. Post-growth treatment to improve color or clarity is common across the industry for both methods and doesn’t change the fact that the stone is a genuine diamond. A full grading report will typically disclose whether treatment was detected.

Does GemsGlitz disclose whether a stone is CVD or HPHT?

We don’t list the growth method per stone. Our diamonds are genuine lab-grown diamonds and, like the rest of our range, are sold without an individual grading report.

Does the growth method affect how a diamond wears day to day?

No. Once cut and set, a lab-grown diamond’s durability and hardness come from being a genuine diamond, not from which growth method produced the rough stone it started as.

If you’d rather focus on the finished piece than the production process behind it, browse our lab-grown diamond rings and pendant necklaces — every stone is a genuine lab-grown diamond, set in 925 sterling silver, chosen for how it looks rather than how it was grown.