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.

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.
• The growth method does not change how a finished diamond looks — cut does.
• Both are graded by the same labs (IGI, GIA) on the same 4Cs.

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.

A brief history

Grown diamonds are not new. The first reproducible diamond was made by General Electric in 1954 using the HPHT method. CVD arrived later and was refined over the following decades; only in the 2010s did it scale to consistent, gem-quality, colourless stones. 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 helps the carbon dissolve and crystallise onto the seed, which grows outward in multiple directions. HPHT is known for strong crystal uniformity and is often chosen for larger stones.

The CVD method (chemical vapour deposition)

CVD is the newer, semiconductor-derived approach. A thin diamond seed 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 it into carbon atoms that settle onto the seed and build the diamond layer by layer. The slow, controlled growth produces very pure crystals — often Type IIa, the type prized for the highest colourless grades.

CVD vs HPHT, side by side

	HPHT	CVD
How it grows	Pressure + 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)
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 more carbon has to crystallise in perfect order. Nature takes one to three billion years; the lab simply 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 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.

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 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 ideal table and depth, three carats minimum, IGI certified. The method is an origin detail; the standard is what reaches your hand. 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.

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