How Are Lab-Grown Diamonds Made?

Laboratory diamonds can be grown by two processes: high pressure, high temperature (HPHT) and chemical vapor deposition (CVD). Some lab-made diamond grading certificates will show how the diamond was made.

CVD vs. HPHT Lab-grown diamonds: What's the difference?

High temperature and pressure method

The HPHT method is the original method of manufacturing laboratory-made diamonds. During HPHT, diamonds are made in the laboratory by replicating the high-pressure, high-temperature conditions that form diamonds underground on Earth.

Gem-grade HPHT diamonds were introduced in the 1950s. In addition to growing diamonds, the HPHT process can also be used to enhance the color of diamonds, making them colorless, pink, green, blue or yellow.

To grow HPHT diamonds, a small diamond seed (a very small diamond) is placed in carbon, the element of which diamonds are made. Diamond seeds are exposed to extreme heat and pressure, replicating the way diamonds naturally grow underground on Earth. Diamond seeds are exposed to temperatures of more than 2,000 degrees Fahrenheit and pressures of about 1.5 million pounds per square inch. The carbon melts and forms diamonds around the seed. It is then cooled and formed into diamonds.

HPHT diamond rough stones are formed differently from CVD diamond rough stones.

HPHT diamonds are more likely to have a pale yellow hue because they are exposed to nitrogen when they are formed. They also tend to contain deeper metal inclusions. These metal inclusions could help scientists identify them as lab-made, since naturally occurring diamonds rarely capture metals during their formation.

Metallic inclusions in high temperature and high pressure diamonds can make diamonds magnetic. That's another way to tell if a diamond was made in a lab -- natural diamonds have no magnetism. A 2012 study showed that more than half of HPHT diamond tests recorded a detectable magnetic response.

Almost all HPHT diamonds are type Ib, which is rare among natural diamonds.

Chemical vapor deposition CVD

The CVD method was created in the 1980s and is newer than the HPHT method. The CVD method mimics how diamonds form in interstellar gas clouds. The CVD method uses less pressure and smaller machinery than the HPHT method.

Diamond seeds are placed in a vacuum chamber by CVD method. The room was filled with carbon-rich gases and heated to nearly 1,500 degrees Fahrenheit. From these extreme temperatures, the gas turns into plasma, leading to the release of carbon fragments. These sheets of carbon pile on top of the diamond seed, allowing the diamond to grow.

The CVD process produces type IIA diamonds, which are extremely rare for natural diamonds. This could help scientists determine whether diamonds were lab-grown or earth-grown. Type IIA diamonds are the most chemically pure diamonds -- they contain no nitrogen and/or boron impurities, unlike HPHT diamonds exposed to nitrogen. CVD diamonds are not magnetic like HPHT diamonds.

Which method is better?

You will not be able to distinguish BETWEEN CVD and HPHT diamonds with the naked eye. Both methods can create beautiful, shiny diamonds. Both the CVD and HPHT methods will produce true diamonds that are optically, chemically and physically identical to those grown on Earth.