How Lab Grown Diamonds Are Made: A Complete Step-by-Step Guide

Lab grown diamonds are made by placing a small diamond seed inside a controlled growth chamber and exposing it to either extreme heat and pressure (HPHT) or a carbon-rich gas plasma (CVD) until a full rough crystal forms over two to four weeks. The result is chemically and physically identical to a mined diamond: pure carbon arranged in the same cubic crystal lattice, scoring 10 on the Mohs hardness scale, and graded by the same 4Cs standards.

What separates lab grown diamonds from simulants like moissanite or cubic zirconia is that starting seed. It is already diamond. The growth process does not create a diamond lookalike; it extends an existing diamond crystal atom by atom until a gem-sized stone is ready for cutting. That distinction matters when you are deciding whether to buy, and it shapes everything that follows in the production sequence.

What is the first step in making a lab grown diamond?

The process starts with seed selection, and the seed is not a grain of sand or a fragment of graphite. It is a precisely cut slice of an existing diamond, typically 1 to 3 millimeters across, chosen for its crystal orientation and structural integrity. Seeds are often sourced from earlier lab grown stones, which keeps the supply chain entirely within controlled conditions.

Before the seed enters any growth chamber, technicians clean it to remove surface contaminants. Even microscopic debris can disrupt how new carbon atoms attach, producing inclusions or growth irregularities that show up later under a grading microscope. The seed’s crystallographic face also matters: the orientation it presents to the incoming carbon determines the shape and quality of the crystal that grows outward from it.

How does the HPHT method grow a diamond?

HPHT, which stands for High Pressure High Temperature, was first developed for industrial use in the 1950s and remains one of the two primary routes to gem-quality lab diamonds today. The seed is placed inside a growth capsule alongside a high-purity carbon source, usually graphite, and a metal catalyst, typically an alloy of nickel, manganese, and cobalt. That capsule goes into a press, either a belt press with two opposing anvils or a cubic press with six.

The press heats the chamber to between 1,300 and 1,600 degrees Celsius while applying pressure in the range of 5 to 6 gigapascals, which is roughly equivalent to 870,000 pounds per square inch. Under those conditions, the metal catalyst melts and dissolves the graphite. Carbon atoms then migrate through the molten metal and precipitate onto the cooler diamond seed, building the crystal outward layer by layer. The growth runs for several days to several weeks depending on the target carat weight. HPHT diamonds tend to emerge with fewer color issues and generally require no post-growth treatment, though the machinery is expensive and growth is slower than the CVD alternative.

How does the CVD method grow a diamond?

CVD, Chemical Vapor Deposition, takes a different approach entirely. The seed is placed inside a vacuum chamber, which is then filled with a mixture of methane and hydrogen gas at much lower pressures than HPHT requires. Microwaves or a hot filament heat the gas mixture to somewhere between 800 and 1,200 degrees Celsius, which ionizes the gas into a plasma. In that plasma state, carbon atoms separate from the methane molecules and deposit directly onto the seed surface, building the diamond one atomic layer at a time.

Because CVD does not require a metal catalyst, the resulting crystals tend to be purer in terms of metallic inclusions. The tradeoff is that the deposition process can introduce nitrogen-vacancy defects that give the rough stone a brownish undertone. Many CVD diamonds therefore go through a secondary HPHT annealing step after growth: the finished rough is placed back into a high-pressure environment, which reorganizes those defects at the atomic level and permanently improves the color. Nothing is added to the stone; the lattice is simply corrected. A full IGI grading report will note whether post-growth treatment was applied, so buyers know exactly what they are purchasing.

What happens after the rough diamond is grown?

Once the rough crystal comes out of either process, it goes through the same finishing stages used for mined stones. The sequence runs: planning, sawing, bruting, faceting, and polishing.

Planning and sawing

Cutters use 3D mapping software to analyze the rough’s internal structure, inclusion placement, and crystal grain before a single blade touches it. The goal is to maximize the yield of carat weight while hitting the target shape. A round brilliant cut from a 1-carat rough, for instance, loses roughly 50 to 60 percent of its starting weight by the time it is polished. Laser sawing then divides the rough into workable pieces based on that plan.

Bruting and faceting

Bruting, also called girdling, rounds the stone into its basic outline shape. Two diamonds are mounted on a spinning axle facing each other and ground together until the girdle takes form. After bruting, a lapper places the main facets and a brillianteer adds the remaining smaller facets, bringing a standard round brilliant to its full 57 or 58 facets. The angle of each facet has to be precise to within a fraction of a degree: angles that are too shallow or too deep cause light to leak out of the pavilion rather than return through the table.

Final polishing

A rotating cast iron wheel charged with diamond powder and oil brings each facet to a mirror surface. This final step is what produces the adamantine luster that distinguishes diamond from every other gemstone.

How is a lab grown diamond certified after polishing?

The finished stone goes to an independent gemological laboratory for grading. In 2026, IGI accounts for the majority of lab grown diamond certifications in global retail. IGI continues to apply the full D-to-Z color scale and FL-to-I3 clarity scale to every lab grown stone it grades, with the 4Cs assessed under standardized laboratory conditions by multiple gemologists working independently. The report also discloses the growth method (HPHT or CVD) and notes any post-growth treatment.

Only specialized spectroscopic equipment, the kind used by IGI and GIA, can identify the growth method by detecting trace inclusions or fluorescence patterns specific to each process. A standard diamond tester or visual inspection cannot tell a lab grown stone from a mined one. The IGI report is what makes the stone’s full story transparent to the buyer.

The Carbon-to-Diamond Journey Ends at the Grading Report

Every lab grown diamond starts as a sliver of existing diamond and finishes as a certified gem that is physically indistinguishable from one pulled out of the ground. The two growth methods, HPHT and CVD, take different paths to the same destination: pure carbon in a cubic crystal lattice. What decides the quality of the finished stone is not which method was used but how carefully each stage was controlled, from seed selection through final polishing and independent certification.

At Ouros Jewels, every lab grown diamond comes with an IGI certificate, so the grading report travels with the stone from the moment it leaves the lab. If you are looking at loose diamonds to understand what the process produces, the Stunning Old Mine Cushion Cut Lab Grown Diamond is a good example of how the post-growth finishing stages shape the final character of a stone.

Frequently Asked Questions

How long does it take to grow a lab grown diamond from start to finish?

Growth alone takes roughly two to four weeks depending on the method and target size, with HPHT tending to run slightly longer than CVD for equivalent carat weights. Add planning, cutting, polishing, and IGI grading, and the full journey from seed to certified gem typically spans six to ten weeks in total.

Are lab grown diamonds real diamonds or just imitations?

Lab grown diamonds are chemically and physically identical to mined diamonds: pure carbon in a cubic crystal lattice, with the same hardness of 10 on the Mohs scale, the same refractive index, and the same thermal conductivity. They are not simulants like moissanite or cubic zirconia, which have different chemical compositions entirely.

Does the HPHT or CVD method produce a better quality diamond?

Neither method is inherently superior. HPHT diamonds typically require no post-growth color treatment, while CVD diamonds often undergo an annealing step to correct brownish undertones. The quality of the finished stone depends on how carefully the growth conditions were controlled and on the cut quality, not on which method was used to grow it.

Can a jeweler tell a lab grown diamond from a mined diamond without special equipment?

No. Standard visual inspection and basic diamond testers cannot distinguish between the two because they share identical optical and chemical properties. Only specialized spectroscopic instruments used by laboratories like IGI or GIA can identify the growth method by detecting specific fluorescence patterns or trace inclusions associated with each process.

Why do some lab grown diamonds go through a second HPHT treatment after CVD growth?

CVD growth can introduce nitrogen-vacancy defects that give the rough stone a brownish tint. A secondary HPHT annealing step reorganizes those defects at the atomic level without adding any material to the stone, permanently improving the color grade. IGI reports disclose this treatment, so buyers can see the complete history of the stone before purchasing.