How Lab-Grown Diamonds Are Made: CVD vs HPHT

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Lab-grown diamonds are made by recreating the exact conditions that form a diamond inside the earth — just faster, and above ground. Two methods do it: HPHT (high pressure, high temperature) presses carbon around a seed the way the earth's mantle does, and CVD (chemical vapour deposition) builds the crystal layer by layer from carbon-rich gas. Both produce a real diamond, identical to a mined one. Here is how each works, what happens after growth, and why the method is a footnote rather than a grade.

Key takeaways

• Every lab-grown diamond starts from a tiny diamond seed and pure carbon — the result is a real diamond, not a simulant.
• HPHT recreates the earth's pressure and heat; CVD grows the crystal from carbon-rich gas.
• Most stones grow in 2–6 weeks (larger ones take longer) — versus a billion-plus years in nature.
• Lab-grown stones are routinely Type IIa, the purest classification, which occurs in only about 1–2% of natural diamonds.
• Some stones receive post-growth treatment to improve colour; reputable laboratories disclose it.
• Growing the crystal and cutting it are two entirely different trades.
• The growth method does not change how a finished diamond looks — cut does.
• Both are graded on the same 4Cs, though the report depends on the laboratory: IGI grades lab-grown diamonds on the full 4C scales, while GIA has issued only a two-tier Premium or Standard classification on lab-grown stones since 1 October 2025.

Are lab-grown diamonds real diamonds?

Yes. Whichever method is used, the result is pure crystallised carbon — physically, chemically and optically identical to a mined diamond, and just as hard (Mohs 10). The only differences from mined are origin and price, which we cover in lab-grown vs mined diamonds. Both techniques begin the same way: with a real diamond seed that the new crystal grows onto, atom by atom, in the same crystal structure. Nothing is being imitated; the process is simply supplying carbon the conditions it needs to arrange itself as diamond.

A brief history

Grown diamonds are not new. The first reproducible diamond was made by General Electric in 1954 using the HPHT method, the culmination of a long research programme to build a press capable of mantle-like pressures. For decades the output was industrial — grit for cutting and drilling, not gemstones. CVD arrived later, borrowed from semiconductor manufacturing, and was refined over the following decades; only in the 2010s did it scale to consistent, gem-quality, colourless stones in sizes that matter for engagement rings. Today both methods routinely produce diamonds that meet — and at Montare must exceed — the standards once reserved for the finest mined stones.

The HPHT method (high pressure, high temperature)

HPHT mimics nature most literally. A diamond seed is surrounded by pure carbon and subjected to the forces found roughly 150 kilometres below the surface: temperatures around 1,300–1,600°C and pressure near 5–6 GPa, on the order of 870,000 psi. A metal flux such as iron or nickel lowers the temperature at which carbon will dissolve and recrystallise onto the seed, which then grows outward in several directions at once. HPHT is known for strong crystal uniformity and is often chosen for larger stones. Its characteristic trace is the occasional inclusion of tiny metallic flux particles from the growth cell — the lab-grown equivalent of the mineral crystals found in mined stones.

The CVD method (chemical vapour deposition)

CVD is the newer, semiconductor-derived approach. A thin diamond seed plate is sealed in a vacuum chamber filled with a carbon-rich gas, typically methane and hydrogen. Microwaves energise the gas into a plasma at around 2,000°C, breaking the methane into carbon atoms that settle onto the seed and build the diamond layer by layer, in one direction. The slow, controlled growth produces very pure crystals — most often Type IIa, the classification prized for the highest colourless grades. Its characteristic trace is a form of striation or graining that follows those growth layers.

Diamond types: the purity scale nobody mentions

Gemologists classify every diamond, mined or grown, by the impurities trapped in its lattice. It is not part of the 4Cs and rarely appears in shop conversation, but it explains why lab-grown stones reach the top colour grades so consistently.

Type	What is in the lattice	Share of natural diamonds
Type Ia	Nitrogen in clustered groups	Roughly 92–98% — the ordinary case
Type Ib	Nitrogen as isolated atoms	Under 1%
Type IIa	Essentially no nitrogen — the purest	About 1–2%
Type IIb	Boron instead of nitrogen; naturally blue	About 0.1%

Nitrogen is what makes a diamond look faintly yellow. In nature, a nitrogen-free Type IIa crystal is a rare accident — one or two stones in a hundred — and historically these were the exceptional diamonds, the ones that ended up in crown jewels. In a growth chamber, the nitrogen simply is not put in. That is the honest explanation for something that otherwise sounds like marketing: lab-grown diamonds reach D and E colour reliably not because they are better diamonds, but because the conditions that produce a colourless crystal can be controlled rather than hoped for.

What happens after growth

A stone does not always come out of the chamber finished. Some CVD diamonds emerge with a faint brown or grey cast and are annealed afterwards — often with a brief HPHT cycle — to clear it. Some HPHT stones receive further cycles to improve colour. These treatments are stable and permanent, unlike the fracture filling used to disguise inclusions in some mined stones, and they do not weaken the diamond.

What matters is disclosure. A reputable laboratory records post-growth treatment on the report, and both IGI and GIA do. This is worth understanding because it is the one place where two stones with the same printed grade can have different histories — and it is a question worth asking of any seller, ours included. We cover the parallel issue for clarity in diamond clarity explained.

From rough crystal to finished diamond

Growing the crystal is only half the work, and the half that gets all the attention. What comes out of an HPHT press or a CVD reactor is rough — an unremarkable-looking crystal that no one would recognise as a gem. It then goes to a diamond cutter, which is a completely separate trade from both diamond growing and jewellery making, with its own apprenticeship and its own tools.

The cutter plans the stone around its shape and any inclusions, then saws, bruts, blocks and polishes it against a spinning wheel charged with diamond powder — because only diamond will cut diamond. A great deal of the rough is lost in the process; a finished stone commonly weighs around half of what the crystal did, and cutting for maximum beauty rather than maximum weight costs more of it still. This is the stage that decides whether a diamond performs, and it is why we hold every stone to Triple Excellent with table and depth in the ideal range for its shape. Growth conditions set the raw material; the cutter decides what it becomes.

CVD vs HPHT, side by side

	HPHT	CVD
How it grows	Pressure and heat around a seed	Carbon gas deposited layer by layer
Conditions	~1,300–1,600°C, ~5–6 GPa	~2,000°C plasma, low pressure
Crystal growth	Multiple directions	One direction (layered)
Characteristic trace	Occasional metallic flux inclusions	Striations along growth layers
Often used for	Larger stones, uniformity	High-purity, top colourless grades
Typical time	Days to a few weeks	2–6 weeks
The finished stone	Real diamond	Real diamond

How long does it take to grow a lab diamond?

Most engagement-ring-sized stones grow in about two to six weeks, depending on size and method. Larger stones — the three-carat-plus centre diamonds Montare specialises in — take longer, sometimes a few months, because far more carbon has to crystallise in perfect order and a single disruption can end the growth run. Nature takes one to three billion years. The lab removes the wait, not the diamond.

Can you tell a CVD or HPHT diamond apart?

Not by eye, and not with a jeweller's loupe. A well-cut CVD and a well-cut HPHT diamond of the same grade are visually identical. Distinguishing them requires specialised laboratory instruments that read microscopic growth patterns, strain and fluorescence — which is exactly why the growth method is recorded on the certificate rather than judged in the showcase. It is a note about origin, not quality. The same instruments are what allow laboratories to separate lab-grown from mined with complete reliability, which is worth knowing given how often the opposite is implied.

Does the growth method affect the diamond you wear?

No, in any way you can see. What actually determines a diamond's beauty is cut — see why Triple Excellent matters and the role of proportions in table and depth explained — and what guarantees its grade is independent certification (IGI vs GIA). If the 4Cs are new to you, start with the 4Cs explained without the jargon. Method is a footnote; cut and certification are the story.

Why it matters at Montare

We do not choose a stone by its growth method — we choose it by its result. Every Montare diamond, CVD or HPHT, is held to one floor: D–E colour, VVS1–VVS2 clarity, Triple Excellent cut with table and depth in the ideal range for that shape, three carats minimum, IGI certified. The per-shape figures are on our standards.

You describe what you are looking for and we source the best stone that clears that floor; our goldsmiths then cast, set and polish the ring by hand in Toronto. Nothing is built for stock, so no ring is hurried to catch a cut-off. Build a ring to that standard in the ring builder, read our guide to buying lab-grown in Canada, or book a consultation.

Frequently asked questions

How are lab-grown diamonds made?

From a diamond seed and pure carbon, using one of two methods. HPHT presses carbon around the seed under extreme heat and pressure; CVD builds the crystal layer by layer from carbon-rich gas energised into a plasma. Both yield a real diamond.

Is CVD or HPHT better?

Neither is better in the finished stone. CVD often produces very high-purity colourless diamonds; HPHT offers strong uniformity and suits larger stones. At a high grade with an excellent cut, they are indistinguishable to the eye.

How long does a lab-grown diamond take to grow?

Roughly two to six weeks for most stones, and up to a few months for large three-carat-plus diamonds — compared with one to three billion years in the earth.

Are CVD and HPHT diamonds real diamonds?

Yes. Both are pure crystallised carbon, identical to mined diamonds in every physical and optical property, and graded by the same independent laboratories.

What is a Type IIa diamond?

Type IIa is the purest diamond classification, containing essentially no nitrogen — the impurity that makes a diamond look faintly yellow. It occurs in only about 1–2% of natural diamonds but is routine in lab-grown stones, because the nitrogen is simply never introduced during growth.

Are lab-grown diamonds treated after they are grown?

Some are. CVD stones with a faint brown or grey cast may be annealed, often with an HPHT cycle, to clear the colour, and some HPHT stones receive further cycles. These treatments are stable and permanent, and reputable laboratories including IGI and GIA disclose them on the report.

Who actually cuts a lab-grown diamond?

A diamond cutter — a separate trade from both diamond growing and jewellery making. The rough crystal is planned, sawn and polished against a wheel charged with diamond powder, since only diamond will cut diamond. A finished stone commonly weighs about half of the rough it came from.

Can a laboratory tell a lab-grown diamond from a mined one?

Yes, reliably. Specialised instruments read microscopic growth patterns, strain and fluorescence that differ between grown and mined crystals. It cannot be done by eye or with a loupe, which is why every stone should come with an independent report.

See the standard, not the method. Design your ring in the ring builder or book a consultation with our Toronto team.