What is the HPHT Process For Lab-Grown Diamonds?

The process for growing HPHT diamonds is more complex and requires larger equipment. This can translate to higher price points for these lab grown gems.

A small diamond seed is placed into carbon and subjected to extreme heat and pressure, replicating the conditions that create Lab diamonds hpht. The diamond is then cooled over the course of weeks.

Belt Press

Diamonds form deep in the Earth, between 177 to 241 km below ground where temperatures can reach up to 1400 degrees Celsius and pressures are nearly 50,000 atm (one atmosphere is equivalent to Earth’s weight). To mimic these conditions in the lab, the HPHT process uses a special container – the growth cell – which contains a diamond seed and highly purified graphite. A series of high-pressure, high temperature cycles are applied to the graphite until it reaches its molten state and begins forming diamonds.

General Electric invented the belt press, which generates an enormous amount of pressure – 1.5 million pounds per square inch – and hot temperatures (over 2,000 degrees Celsius) that make it possible to grow gem-quality lab created diamonds. While GE’s first laboratory grown diamond was tiny and heavily included, it laid the foundation for more modern cubic and split-sphere processes that have since produced larger gem-quality lab diamonds.

Increasingly, people are turning to lab created diamonds as an ethical and environmentally responsible alternative to mined gemstones. In fact, it’s estimated that by 2022, 80% of all diamonds will be lab created, partly due to increased awareness among consumers and jewelers. This has been aided by a steady stream of media coverage from big name jewelry brands and local jewelers, as well as research that suggests Gen Z is more likely to choose a lab created diamond engagement ring over a mined one due to its lower price and environmental benefits.

Cubic Press

Diamonds form under extreme heat and pressure, similar to those found deep within the earth. The first lab grown diamond was created by General Electric in 1954 using their belt press machine which uses an upper and lower anvil to generate over 1.5 million pounds per square inch of pressure to melt raw carbon (graphite) around a small diamond seed. Over time, the new diamond crystal grows until it is cut and polished into its final gem form.

In addition to being a lot cheaper and more energy efficient than mining natural diamonds, the HPHT process also produces higher quality diamonds. It is the most common way that we see colorless and near-colorless lab created diamonds in fine jewelry today.

The process itself requires a large chamber which is filled with pure carbon, a mixture of metals called a catalyst and a small diamond seed. This mixture is heated to over 1,300 degrees Celsius with a combination of over 50,000 atmospheres of pressure and ionized gases which are injected into the growth cell. Over days or weeks, the molten carbon bonds together creating a diamond.

This process is very effective when it comes to creating larger lab-created diamonds and is the most commonly used method for creating the lab created diamonds we see in fine jewelry today. The HPHT process can create a diamond of up to 15 carats with a good degree of clarity.

Split-Sphere Press

The Split-Sphere Press process uses eight outer anvils and six smaller inner anvils to maximize the amount of pressure that is put on the capsule. This allows the diamond to form more quickly, and it also results in a higher quality lab-grown diamond.

This is the oldest technique for creating lab grown diamonds, and it was designed to mimic the conditions found in nature where natural diamonds are formed. The process starts with a small piece of carbon starting material (usually graphite) and places it into a capsule. This is then placed into an apparatus that generates high temperatures and pressures.

Inside the capsule, the starting material dissolves in a liquid flux that contains iron, nickel, and cobalt. The metals lower the temperature and pressure needed to create a diamond, and they are also used to give the diamond its color. During this phase, the starting material can absorb nitrogen or boron which gives it a yellowish or blueish color respectively.

After the molten flux has dissolved, a layer of pure carbon is deposited on top of the diamond seed. Then the diamond starts to build up atom by atom, layer by layer into a larger crystal. The CVD method was developed more recently and is seen as less expensive than HPHT, as it doesn’t need the same levels of high pressure or temperature.


In today’s market, lab grown diamonds are in high demand due to their social and environmental benefits. As the popularity of these gems grows, it is important for shoppers to understand the different processes that are used to produce them so they can choose a product that best meets their needs.

Two of the main successful methods to produce lab grown diamonds are HPHT and CVD. Each has its own unique characteristics, but both can be identified by a number of indicators. In the end, it comes down to your hpht vs cvd personal preferences and budget, as lab grown diamonds are generally around 40% less expensive than mined diamonds and have a transparent supply chain and sustainable energy source.

During the CVD process, a thin wafer of a diamond crystal is placed into a vacuum chamber and heated to 800 degrees Celsius. Then, it is filled with carbon-rich gases like methane which are ionized into plasma by microwaves or lasers and deposited onto the diamond seed crystal layer by layer. This builds up the diamond to a desirable size without the need for any high pressure or temperature.


As the diamonds build, they can sometimes develop a rough edge of black graphite that must be polished away prior to faceting. Additionally, these diamonds may have metallic inclusions which can help scientists identify them as lab grown. This is because naturally formed diamonds do not capture metals during their formation.