How Lab Grown Diamonds Are Made: HPHT vs CVD in Plain English

A lab grown diamond is real diamond by every measure a gemologist can run: same carbon, same crystal structure, same hardness, same fire. What changed is the birthplace. Instead of forming under a continent over a billion years, the stone grew inside a machine over a few weeks. Two very different machines, actually. Here is how both work, and whether the method should influence what you buy.

First, What a Diamond Actually Is

A diamond is carbon atoms locked into a specific cubic crystal structure. That arrangement is what makes diamond the hardest known natural material and gives it the sharp refraction and rainbow dispersion no imitation quite matches. Grow that same structure anywhere, and you have grown a diamond.

Regulators agree. In 2018 the US Federal Trade Commission revised its Jewelry Guides and removed the word "natural" from its definition of a diamond, on the logic that a diamond grown above ground is the same material as one pulled out of it. Sellers still have to disclose that a stone is lab grown, which is exactly as it should be, but the material itself carries no asterisk.

HPHT: The Pressure Cooker

HPHT stands for high pressure, high temperature, and it came first. General Electric grew the first verifiable synthetic diamonds in December 1954 and announced them the following year: tiny gray grit destined for cutting tools, not ring fingers. It took decades of refinement before HPHT presses could grow clean, colorless crystals large enough to facet for fine jewelry.

The process imitates how the earth does it. A small diamond seed sits in a growth cell with a carbon source and a metal catalyst, typically iron, nickel, or cobalt. A press squeezes the cell to pressures like those found roughly a hundred miles underground while heating it well past 1,300 degrees Celsius. The metal melts, dissolves the carbon, and the dissolved carbon migrates to the slightly cooler seed, where it crystallizes as diamond. Days to a couple of weeks later, out comes a rough crystal ready for the cutting wheel.

HPHT stones sometimes carry microscopic traces of that metal catalyst, and a few pick up a faint blue nuance from boron during growth. When either matters, it shows up on the grading report.

CVD: Diamond, One Layer at a Time

CVD stands for chemical vapor deposition, and it works at the opposite end of the pressure scale. Instead of crushing carbon, a CVD reactor grows diamond in a near vacuum.

Thin diamond seed plates go into a chamber filled with a little methane and a lot of hydrogen. Microwave energy turns the gas into a plasma hot enough to strip the methane apart, and the freed carbon atoms settle onto the seed plates, extending the crystal one atomic layer at a time. Growing enough rough for a one carat polished stone typically takes a few weeks.

Many CVD crystals come out of the reactor with a brownish or grayish cast, so growers often give them a short HPHT treatment afterward to improve the color. The treatment is permanent and stable, and it gets disclosed: a report that reads "as grown" means the stone needed no help. Some buyers prefer that, and it is a fair thing to prefer.

Which Method Grows the Better Diamond?

Neither, as a category. Both methods now produce stones across the full range of color and clarity, from forgettable to flawless. A well-grown CVD stone beats a mediocre HPHT stone, and the reverse is just as true.

Judge the stone, not the reactor. The grading report tells you color, clarity, cut, and any post-growth treatment, and those facts matter far more than the acronym. If you want one practical question to ask a jeweler, make it this: if the stone is CVD, is it as grown or treated? Either answer is fine. You just deserve to know it.

Why Growing Got So Cheap

Reactors got better, growers multiplied, and competition did what competition does, especially as producers in India and China scaled up. The cost of growing a bright, well-cut stone has dropped for a decade straight, and retail prices followed. That trend is rough on resale, which we covered honestly in our lab diamond resale guide, and wonderful for wearing. A size and quality that read as a fantasy budget in 2015 is an ordinary decision now.

Can Anyone Tell It Apart From a Mined Diamond?

Not by looking. Not with a loupe, and not with the thermal testers used at jewelry counters, which correctly read lab grown stones as diamond because that is what they are. Separating grown from mined takes laboratory instruments that analyze fluorescence patterns and growth structure, which is exactly why grading labs handle identification and inscribe the results. Most lab grown diamonds carry a microscopic laser inscription on the girdle with the report number, invisible to the naked eye and easy to verify under magnification.

How the House Uses This

Ultimate Diamond has been sorting and setting stones on New York's 47th Street since 1959, long before either acronym reached a jewelry counter. Le Fling, the membership built on that inventory, uses lab grown diamonds exclusively, set in 14k and 18k gold, because grown stones fit how the membership works. Members rotate real diamonds at sizes that would be a serious decision to buy outright, every payment builds ownership credit, and the piece that earns a permanent spot can be bought at 20% off retail. The machines brought the price down. The house makes sure what comes out of them is worth setting.

People Also Ask

Are lab grown diamonds real diamonds?

Yes. Same carbon, same crystal structure, same hardness at 10 on the Mohs scale, same optical behavior. The FTC defines them as diamonds, and grading labs evaluate them with the same instruments they use on mined stones. The honest differences are origin, price, and resale behavior, not the material.

Do lab grown diamonds pass a diamond tester?

Yes. Standard handheld testers measure thermal conductivity, and lab grown diamonds conduct heat exactly the way mined diamonds do. Simulants like cubic zirconia fail that test. Telling grown from mined requires laboratory equipment, not a pen tester.

Do lab grown diamonds get cloudy or fade over time?

No. Diamond does not oxidize, yellow, or degrade with wear, regardless of where it formed. If a lab grown stone looks dull, the culprit is skin oil and lotion film on the surface, and warm water with a drop of dish soap fixes it in minutes.

Is HPHT or CVD better?

Neither method is better across the board. Both produce top-grade stones and both produce mediocre ones. Buy the grading report: color, clarity, cut, and treatment disclosure tell you everything the acronym does not.