How Scientists Discovered the Two Methods Used to Grow Diamonds in a Lab

The two methods used to grow diamonds in a lab are High Pressure High Temperature (HPHT), which replicates the crushing conditions of Earth’s mantle, and Chemical Vapor Deposition (CVD), which assembles a diamond carbon atom by atom from a gas mixture. Both produce stones with identical chemical composition and crystal structure to mined diamonds, but each leaves a different fingerprint: HPHT stones can retain metallic flux inclusions from the growth catalyst, while CVD stones sometimes show strain birefringence from the layered deposition process. These signatures are how a gemologist reading an IGI report can tell which reactor a stone came from.

The two methods emerged from entirely separate scientific traditions in the early 1950s, which is why they look so different under the microscope despite arriving at the same result.

Why Did Scientists Think High Pressure Was the Answer?

The assumption was logical. Natural diamonds form roughly 100 miles below Earth’s surface, where temperatures reach around 1,000°C and pressures exceed 50,000 atmospheres. Geologists had understood this since the late 19th century, so the first teams to attempt synthesis simply tried to recreate those conditions in a laboratory press.

The Swedish company ASEA made the first credible attempt in 1953, running a secret high-pressure experiment that likely produced tiny diamonds but was never published at the time. General Electric’s team in Schenectady, New York, achieved a confirmed and documented synthesis in December 1954, using a belt press that squeezed a carbon source and a metal catalyst, typically iron or nickel, at extreme pressure and heat. The molten metal dissolved the carbon and then redeposited it as diamond crystals around a small seed. GE announced the result publicly in 1955, and the HPHT method has been refined continuously since.

How the HPHT press works today

Modern HPHT equipment still follows the same principle GE demonstrated in 1954. A diamond seed is placed inside a growth cell with a carbon source, usually graphite, and a metal catalyst. The press applies roughly 55,000 to 65,000 atmospheres of pressure at temperatures between 1,300°C and 1,600°C. Carbon dissolves into the molten catalyst, migrates toward the cooler seed crystal, and crystallizes as diamond over a period of days to weeks. The resulting stones tend to grow in a cuboctahedral pattern, which produces the characteristic inclusion shapes that gemologists look for when identifying HPHT origin.

How Did a Completely Different Approach Emerge from Chemistry?

CVD took shape through plasma physics rather than geology. Researchers studying carbon films in the 1950s and 1960s noticed that certain gas-phase reactions could deposit thin layers of carbon on surfaces. The insight that this carbon could organize itself into diamond’s crystal lattice, rather than softer graphite, came gradually through work at the Soviet Academy of Sciences in the 1970s and was refined by teams at the National Institute of Standards and Technology in the United States during the 1980s.

By the mid-1980s, researchers had demonstrated that a mixture of methane and hydrogen gas, energized by microwave plasma or a hot filament, would break down and rain carbon atoms onto a substrate. At the right temperature, around 700°C to 1,000°C, those atoms arranged themselves into diamond rather than graphite. The hydrogen in the mix plays a critical role: it preferentially etches away graphite bonds, leaving only diamond bonds intact.

How CVD grows a diamond layer by layer

In a modern CVD reactor, a thin diamond seed wafer is placed inside a vacuum chamber. A gas blend, typically 1 to 5 percent methane in hydrogen, is introduced and energized by microwave radiation until it becomes plasma. Carbon atoms rain down onto the seed and build up the crystal one atomic layer at a time. The process runs for weeks, and the resulting rough stone is a flat slab that is then cut and polished. CVD diamonds grow in a columnar pattern, which is why they can show strain birefringence when viewed under polarized light. This optical effect is not a flaw in quality; it is simply a record of how the stone was assembled.

Do Lab Grown Diamonds Carry the Same Grading Standards as Mined Stones?

Knowing the growth method matters at the point of purchase because it appears on the grading report. The International Gemological Institute (IGI) certifies lab grown diamonds using the same 4Cs criteria applied to mined stones, and the report will note whether the diamond was produced by HPHT or CVD. Neither method produces an inferior diamond. The choice between them comes down to the specific stone’s characteristics: cut, color, clarity, and carat weight, not the reactor it grew in.

The Process, Not the Origin, Is What Shapes the Stone

Both HPHT and CVD were discovered because scientists were asking different questions. HPHT researchers were trying to copy nature; CVD researchers were asking whether gas-phase chemistry could do the same job. The fact that both paths led to real, certifiable diamonds is less a coincidence than a reflection of diamond’s underlying stability as a carbon structure. Once you understand the two methods, the grading report stops being a formality and starts being a readable record of how your stone was built. If you want to see that documentation in practice, the IGI Certified Round Lab Grown Diamond Stud Earrings from Ouros Jewels come with full grading certificates that specify the growth method alongside the 4Cs.

Frequently Asked Questions

Is an HPHT diamond the same quality as a CVD diamond?

Yes. Both HPHT and CVD diamonds are chemically and optically identical to mined diamonds and are graded on the same 4Cs scale by laboratories like IGI. Quality differences between individual stones come from cut, clarity, and color, not from which growth method was used. The method is noted on the certificate but does not determine value by itself.

Can a jeweler tell whether a lab diamond was made by HPHT or CVD without a certificate?

A trained gemologist using specialized equipment can usually distinguish the two. HPHT stones may show metallic flux inclusions and a cuboctahedral growth pattern under magnification. CVD stones sometimes display strain birefringence under polarized light. Standard visual inspection at the counter will not reveal the difference; laboratory testing is needed for a definitive answer.

Do HPHT and CVD lab grown diamonds test as real diamonds on a diamond tester?

Yes. Both types register as genuine diamond on standard thermal conductivity testers because they share the same crystal structure and thermal properties as mined diamonds. Moissanite testers that also check electrical conductivity will correctly identify both lab grown types as diamond, distinguishing them from simulants like cubic zirconia.

How long does it take to grow a lab diamond using CVD?

A CVD reactor typically takes two to four weeks to grow a rough diamond of one to two carats, depending on the target size and the specific equipment used. HPHT growth is generally faster for smaller stones but slower for larger ones. After growth, the rough stone still requires cutting and polishing, which adds additional time before it becomes a finished gem.

Why do some lab grown diamonds cost more than others if they are all made in a lab?

Price reflects the finished stone’s 4Cs grade, not just the production method. A two-carat CVD diamond with VS1 clarity and D color costs more than a one-carat HPHT stone with SI1 clarity and G color because the grading criteria are the same as for mined diamonds. Larger, higher-clarity, better-color stones require more precise growth conditions and more careful cutting, which raises cost regardless of the reactor type.