How Are Lab-Grown Diamonds Made? HPHT, CVD and the Journey from Seed to Ring

How are lab-grown diamonds made? The short version

A lab-grown diamond is real diamond: carbon atoms locked in the same cubic crystal structure as a mined stone, with the same hardness (10 on the Mohs scale, the scale gemmologists use for scratch resistance), the same refractive index of 2.42 (how strongly it bends light) and the same density of about 3.52. Only the origin is different. Our explainer on whether lab-grown diamonds are real covers the science; this page follows the stone through the factory.

Every lab-grown diamond starts as a seed: a small piece or thin slice of diamond that gives new carbon atoms a pattern to copy. From there the journey has five stages:

• Growth: carbon is added to the seed by high pressure, high temperature (HPHT) or chemical vapour deposition (CVD).
• Sorting the rough: the raw crystal is cleaned, weighed and inspected for colour, inclusions and strain.
• Post-growth treatment (if needed): many crystals are heated again to improve their colour.
• Cutting and polishing: the rough is planned, sawn and faceted on the same equipment used for natural diamonds.
• Grading and inscription: an independent laboratory confirms it is laboratory-grown, grades it and laser-inscribes the girdle.

The first reproducible laboratory diamonds were made in the 1950s, mostly as tiny crystals for industrial cutting and grinding. Gem-quality crystals followed around 1970, but only in roughly the last decade has production become large and consistent enough for everyday jewellery. Most gem-quality lab-grown rough today is grown in China and India. For the wider buying picture, start with our complete lab-grown diamonds guide.

How are lab-grown diamonds made with HPHT?

HPHT stands for high pressure, high temperature. It recreates, inside a press, the conditions deep in the earth's mantle (roughly 150 to 200 kilometres down) where natural diamonds formed, mostly 1 to 3 billion years ago.

At the heart of the press is a small growth cell. Growers load it with three things: a carbon source (usually high-purity graphite), a metal solvent (an alloy of iron, nickel or cobalt that melts and dissolves carbon) and one or more seed diamonds at the slightly cooler end. The press squeezes the cell to about 5–6 gigapascals, roughly 50,000 to 60,000 times the air pressure around you, and heats it to about 1,300–1,600°C. The graphite dissolves in the molten metal, drifts towards the cooler seed and crystallises on it as diamond, layer by layer.

There are three main press designs. The cubic press, with six anvils pushing in from every side, is the workhorse of large-scale production in China. The older belt press uses two anvils and a ring, and the split-sphere (BARS) press uses nested anvils inside a pressurised vessel. A single growth run usually takes from a few days to around two weeks, depending on the size of crystal wanted.

HPHT crystals have a recognisable shape, a cuboctahedron that combines square cube faces with triangular octahedral faces. Their colour depends on what slips into the crystal: nitrogen turns it yellow, boron turns it blue, so growers add 'getters' such as titanium or aluminium to soak up nitrogen and produce colourless stones. Tiny specks of the metal solvent can become trapped as inclusions, and a stone with enough of them may be weakly attracted to a strong magnet, one of the clues laboratories use. A basic thermal tester cannot see any of this, which is why standard diamond testers read lab-grown stones as diamond.

How are lab-grown diamonds made with CVD?

CVD stands for chemical vapour deposition. Instead of crushing carbon into diamond, it builds diamond atom by atom from a gas, at pressures well below normal air pressure.

Growers lay thin, square seed plates of diamond, commonly up to about 10 mm across, on a holder inside a sealed vacuum chamber. The chamber is filled with mostly hydrogen and a small amount of methane, typically a few per cent. Microwave energy then ignites a plasma, a glowing ball of electrically charged gas, just above the seeds, which sit at roughly 800–1,200°C. The plasma breaks the methane apart, carbon settles onto the seed surface and copies its crystal structure, while the hydrogen etches away any carbon that tries to form as graphite instead of diamond.

Growth is slow and steady, typically a few to a few tens of micrometres an hour. Building a crystal thick enough to cut a 1–2 carat stone usually takes about two to four weeks, and growers often stop the run, clean or polish the top surface and start again. A single reactor can grow dozens of seeds at once. The finished crystals are flat, square blocks with a dark rim of polycrystalline diamond and graphite around the edges, which is sawn off before cutting.

Straight out of the reactor, many CVD crystals have a brownish or greyish tint caused by tiny distortions in the crystal lattice. That is why so many CVD stones are given post-growth treatment, covered below. Because the crystal grows in layers, some stones also show faint parallel banding or strain under magnification; our guide on what CVD growth striations mean for buyers explains when it matters and when it does not.

HPHT vs CVD diamonds: is one method better?

Neither method makes a better diamond on its own. A well-grown, well-cut HPHT stone and a well-grown, well-cut CVD stone can grade identically and look the same on the hand. Both usually end up as type IIa, the chemically purest diamond type with almost no nitrogen, which is rare among natural diamonds (only around 1–2% of mined stones). What matters is the individual stone: its colour, clarity, cut and whether it has been treated. Our guide to how lab-grown colour grades work explains why two stones with the same grade can still look slightly different.

What happens after a lab diamond is grown?

Once the crystal comes out of the press or reactor, it is cleaned in acid to remove metal or graphite, weighed and examined. Stones that need it then go through post-growth treatment, a second process that changes the colour after growth.

• HPHT annealing: the most common treatment. A CVD crystal is placed in an HPHT press for a short time, usually minutes to hours, which relaxes the lattice distortions that cause brown tints and lifts the colour towards colourless.
• Irradiation and annealing: used to create fancy colours such as pink, red or some blues, by deliberately creating and then stabilising colour centres in the crystal.
• Low-pressure annealing: heating without high pressure, sometimes used to adjust colour or reduce strain.

These treatments are permanent under normal wear and care, and they must be disclosed. Most reports state either 'as grown' or that the stone has been treated after growth. Our page on post-growth treatment in lab-grown diamonds goes through the report wording and whether it should affect your choice.

How are lab-grown diamonds cut and polished?

From this point, a lab-grown diamond is handled exactly like a natural one. Most gem-quality rough, whichever country grew it, is cut in India, especially in Surat, using the same machines and the same skilled cutters.

• Mapping: the rough is scanned in 3D and software plans the shapes and sizes that make good use of the crystal while avoiding inclusions.
• Sawing: a laser cuts the crystal along the planned lines. CVD's flat blocks suit shapes such as cushions, emerald cuts and ovals as well as rounds.
• Bruting or girdling: the outline of the stone is shaped.
• Faceting: each facet is polished on a spinning cast-iron wheel, called a scaife, coated with diamond powder. Only diamond can polish diamond, so a lab-grown stone takes exactly the same effort to cut as a natural one.

Typically only around a third to a half of the rough weight survives as polished diamond. Because lab-grown rough costs far less than mined rough, some cutters chase weight or speed rather than proportions, so cut quality still varies widely. Our guide to judging lab-grown cut quality shows what to check. The steady supply does have one real advantage: it is much easier to find stones with near-identical measurements and colour, which helps when pairing two lab-grown diamonds for studs or sourcing dozens of small stones for tennis bracelets and earrings.

Can you tell if a diamond is lab-grown?

Not by eye, and usually not with a 10× loupe either. Gemmological laboratories separate natural from laboratory-grown diamond with instruments: spectroscopy (reading how the stone absorbs or emits light to detect tiny traces of nitrogen, silicon or boron) and fluorescence imaging such as the DiamondView, which shows the growth pattern inside the stone. HPHT stones show cube-and-octahedron growth sectors, CVD stones show fine parallel layers, and natural diamonds show the octahedral growth they formed with underground.

That table is why a lab-grown diamond belongs in a different category from a simulant (a material that only imitates diamond). See our comparisons of lab-grown diamond and cubic zirconia and lab-grown diamond and moissanite for how each looks and wears.

Independent reports are your proof. IGI grades most lab-grown diamonds sold in Australia and usually notes the growth method. GIA reports on lab-grown stones now use broader quality descriptions rather than the full colour and clarity scale; our guide to GIA's premium and standard lab-grown assessments explains the change. Most graded lab-grown stones also carry a laser inscription on the girdle with the report number and a marking such as 'LABORATORY-GROWN' or 'LG'.

Does the growing method affect price, and what must sellers disclose in Australia?

The method itself has little effect on price. What moves the price is the same as any diamond, carat, colour, clarity and cut, plus how efficiently the stone was produced. Lab-grown prices have fallen steeply as reactors and presses have become larger and faster. As a rough guide, a well-cut 1 carat lab-grown diamond in about F–G colour and VS clarity sells loose for roughly AUD 1,000–3,000, while a natural diamond of similar grades is typically around AUD 8,000–15,000 or more. Our guide to what really drives lab-grown prices explains the gap, and choosing a 1 carat lab-grown stone shows where to spend.

Natural and lab-grown diamonds are different products with different stories: natural stones are rare and formed billions of years ago; lab-grown stones are the same material made in weeks at a fraction of the cost. Neither is the wrong choice. Our side-by-side look at lab-grown and natural diamonds compares them honestly.

Under the Australian Consumer Law, a seller must not mislead you about what a product is. In practice that means a lab-grown diamond should be clearly described as lab-grown or laboratory-grown wherever it is called a diamond, on the label, the invoice and the report. Claims about ethics or the environment also need real evidence behind them, because production uses large amounts of electricity and the energy source varies by factory. Our guide to using ethical sourcing terms carefully explains what is and is not fair to say.

Once it is in a ring, a lab-grown diamond behaves exactly like a natural one. It is worth insuring your lab-grown diamond for its replacement value, and it needs no special treatment: lab-grown diamond care is the same warm water, mild detergent and soft brush you would use for any diamond.

How to check how your lab-grown diamond was made: step by step

1. Ask for the grading report. Every lab-grown centre stone should come with one from an independent laboratory such as IGI or GIA.
2. Find the growth method. Look for 'HPHT' or 'CVD' in the comments or origin section of the report.
3. Look for the treatment note. 'As grown' means no colour treatment; any post-growth treatment should be stated plainly.
4. Check the inscription. Under a 10× loupe, the girdle should show the report number and a lab-grown marking that matches the report.
5. Look at the stone itself. In daylight or a 360° video, check for any brown or grey tint and for visible banding that the grade may not reveal.
6. Decide where to buy. Our comparison of buying lab-grown online or in a showroom covers what you can and cannot check remotely.
7. Look up anything unfamiliar. Terms like type IIa, annealing or strain are explained in our jewellery and gemstone glossary.