How Are Lab Grown Diamonds Made? The Full Process, From Seed to Certified Stone
A lab-grown diamond is made by growing a new diamond crystal from a tiny piece of diamond called a seed. This is done using either HPHT, which uses high pressure and heat, or CVD, which grows the diamond from a carbon-rich gas.
Growing the rough diamond can take anywhere from a few hours to several weeks. After that, the rough crystal is cut, polished, and graded. Let’s understand both these methods of making lab-grown diamonds in depth.
What Lab-Grown Diamonds Are Made Of
A lab-grown diamond is made of carbon atoms arranged in the same crystal structure as a mined diamond. The U.S. Federal Trade Commission's Jewelry Guides define a diamond as a mineral made mainly of carbon in a specific crystal structure.
The definition does not say that a diamond must come from the ground. The Guides also say that sellers should clearly tell buyers when a diamond is laboratory-grown.
The source of carbon depends on the method used. HPHT uses graphite, while CVD uses methane gas. Small amounts of other elements can change a diamond's color.
Lab-grown diamonds can also come in colors such as blue, green, and red. These colors are created by adding or controlling certain elements during the growth process. For example, nitrogen can give a diamond a yellow color, while boron can give it a blue color. Growers can also add specific elements in controlled amounts to create other colors.
The Diamond Seed
The diamond seed is a thin piece of diamond that comes from either a natural or lab-grown diamond. It is an important part of the lab-grown diamond making process because new carbon atoms need a diamond surface to build on.
The seed gives them the right crystal pattern to follow as the new diamond grows. Think of it as a starting point for the new diamond to grow. The seed's size, quality, and preparation can all affect the final stone.
HPHT: How Pressure and Heat Grow a Diamond
HPHT stands for high pressure, high temperature. It is the older of the two main methods used to make gem-quality lab-grown diamonds. The process recreates some of the extreme conditions found deep inside the Earth where natural diamonds form.
Inside the chamber, graphite, a metal mixture (usually nickel and cobalt), and a diamond seed are placed under very high pressure. The pressure reaches about 5–6 GPa, while the temperature reaches around 1,300–1,600°C. That's similar to the pressure found roughly 150–190 kilometers below Earth's surface.
The extreme heat melts the metal, which then dissolves the graphite. As the carbon-rich metal reaches the diamond seed, the carbon comes out of the metal and attaches to the seed. Layer by layer, the carbon forms a new diamond crystal.
The high temperature helps the diamond grow much faster than it would naturally. Depending on its size and quality, the growth can take anywhere from about an hour to a few weeks. Once the rough diamond is fully grown, the chamber is cooled, and the crystal is removed.
CVD: How a Diamond Is Built From Gas
CVD stands for chemical vapor deposition. Unlike HPHT, it does not use molten metal or extremely high pressure. Instead, it grows a diamond from carbon-rich gas inside a special chamber.
You may see both HPHT and CVD described as methods that copy how diamonds form in nature. This is true for HPHT because it recreates the conditions found deep inside the Earth. CVD is different. It is a chemical process that happens in a gas and is very different from how natural diamonds form.
In the CVD method, hydrogen and methane gases flow into a vacuum chamber containing one or more diamond seeds. Microwaves heat the gases and turn them into plasma, which breaks the gas molecules apart. The carbon from the methane then settles on the diamond seeds and follows their crystal structure.
This process uses a disc with 15 - 30 diamond seeds inside a chamber heated to about 700 - 1,200°C. Hydrogen makes up about 90–99% of the gas mixture. It does not provide the carbon for the diamond. Instead, it helps prevent unwanted graphite and other types of carbon from forming on the growing diamond.
Layer by Layer
The diamond grows one thin layer at a time over several days or weeks. The process needs regular attention because unwanted carbon can build up on the surface.
If needed, growers may remove the diamonds every few days and polish the surface before putting them back into the chamber. This can happen several times during the growth process, and the full process may take three to four weeks.
These stoping can leave faint lines inside the diamond. You can't see them with the naked eye, but they can show up under deep-ultraviolet imaging used by gemological laboratories. These lines can help identify a CVD-grown diamond.
Color Finishing After CVD Process
A CVD diamond is not always finished when it comes out of the reactor. Some CVD diamonds have a brownish tint and need additional treatment to improve their color.
In this process, the diamond is heated to more than 1,600°C using HPHT treatment. Another similar method, called low-pressure, high-temperature (LPHT) annealing, heats the diamond in a vacuum or inert gas. Both methods can reduce or remove the brown color.
This treatment does not add any new diamond material to the stone. It only removes some of the defects inside the crystal. Natural brown diamonds can also be treated similarly. Color finishing treatment is quite common. About 80% of the CVD diamonds submitted to GIA since 2020 showed signs of post-growth treatment.
From Rough Crystal to Certified Gem: Cutting, Polishing and Grading
The diamond that comes out of the press or reactor is still a rough crystal. It needs to be planned, cut, shaped, and polished before it becomes a finished gemstone ready to go into jewelry.
Why the Cutter Starts With a Different Crystal
Lab-grown diamond crystals can have a different shape from natural rough diamonds. Because of this, cutters plan the cut carefully to keep as much of the diamond's weight as possible.
About 70% of the natural diamonds GIA examined were round. Large lab-grown diamonds, especially those of 4 carats or larger, have a mix of shapes. GIA says this is partly because cutters try to keep more of the original crystal's weight.
The way a diamond is cut has a major effect on how it reflects and handles light, which is why cutting matters just as much as the growth process when it comes to the finished diamond. Surat, India, is one of the world's major diamond cutting and polishing centers and is also home to many CVD diamond growers.
Grading, Inscription and Traceability
Lab-grown diamonds are graded using the same 4Cs as mined diamonds: carat weight, color, clarity, and cut. GIA has been grading lab-grown diamonds since 2007, and IGI is another major gemological laboratory that grades them.
Lab-grown diamonds also have a “LABORATORY-GROWN” inscription or a manufacturer's marking on the girdle, which is the thin edge around the diamond. This marking helps identify the stone as lab-grown.
HPHT vs CVD: Does the Method Change the Diamond You Get?
Not really. The diamond growth method alone should not decide which diamond you buy. Both HPHT and CVD diamonds are graded using the same standards for carat weight, color, clarity, and cut.
The two methods are just different in how the diamond is grown. You may have heard that CVD is better for large diamonds while HPHT is better for smaller ones. But this is no longer a reliable rule.
HPHT is widely used for melee diamonds, which are very small diamonds used as accents. At the same time, HPHT is also being used to grow larger diamonds. CVD also makes many of the commercial-size diamonds.
Two lab-grown diamonds with the same carat weight can look very different because of their cut, color, and clarity. So if a seller says one growth method is better, look at the grading report for the actual diamond rather than choosing based only on whether it is HPHT or CVD.
Is the Process Sustainable? What the Energy Numbers Show
Growing a diamond uses a lot of heat and electricity, so it's fair to ask how environmentally friendly the process really is. The answer depends on the growth method, the equipment, and the source of the electricity.
We cover this topic in more detail in our other guide, where you can learn more about how ethical lab-grown diamonds really are and whether their environmental claims hold up.
What the Growth Process Means When You Buy
When you're buying a lab-grown diamond, you don't need to focus too much on how it was grown. Instead, keep these points in mind:
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Don't choose based only on the growth method.
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Check the grading report.
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Check the inscription.
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Focus on the cut.
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Ask about energy use if sustainability matters to you.
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Choose a report from a recognized laboratory, such as GIA or IGI.
Read Our Other Guides To Know More About Lab-Grown Diamonds:
After learning all this, if you're ready to buy lab diamond jewelry, our lab-grown diamond engagement rings are a practical place to use this checklist.
