Most people know lab-grown diamonds exist. Far fewer know how they are actually made.
That gap matters. When you understand the process, you stop second-guessing the product. You see why a lab-grown diamond is not a shortcut or a cheap imitation. It is a scientific achievement that took decades to perfect.
There are two methods used today: Chemical Vapour Deposition (CVD) and High Pressure High Temperature (HPHT). Both produce real, certified diamonds. They just take different routes to get there.
This guide explains both, clearly, without drowning you in chemistry jargon.
First, What Is a Diamond Seed?
Before either process begins, you need a diamond seed. This is a tiny, thin slice of an existing diamond, roughly the size of a fingernail, used as the foundation on which the new diamond grows.
Think of it like a starter culture in yogurt. You need a little of the real thing to grow more of the real thing. The seed is real diamond. Everything that grows from it is real diamond too.
Method 1: CVD or Chemical Vapour Deposition
Step 1: The Chamber
The diamond seed is placed inside a sealed vacuum chamber. The chamber is pumped out and filled with carbon-rich gases, usually a mix of methane and hydrogen.
Step 2: Activating the Gas
The chamber is heated to around 700 to 1,000 degrees Celsius. Microwave energy or laser technology ionises the gas, breaking molecular bonds and creating a plasma cloud of carbon atoms.
Step 3: Carbon Builds Up
Those freed carbon atoms rain down onto the diamond seed and attach themselves to its crystal structure, layer by microscopic layer. The diamond grows upward, one atomic layer at a time.
Step 4: Growth and Shaping
This process runs for several weeks. The result is a rough diamond crystal. It is then cut, polished, and graded exactly like a mined diamond rough.
Why CVD Matters
It produces Type IIa diamonds, the chemically purest form of diamond. Less than 2% of all natural mined diamonds are Type IIa. In CVD, this level of purity is the standard outcome.
Method 2: HPHT or High Pressure High Temperature
Step 1: The Press
A carbon source, typically graphite or carbon powder, is placed alongside a diamond seed and a metal catalyst, usually a combination of iron, nickel, or cobalt. This assembly is loaded into a specialised press.
Step 2: Extreme Conditions
The press subjects the material to pressures of around 5 to 6 gigapascals and temperatures of 1,300 to 1,600 degrees Celsius. To put that in perspective, 5 gigapascals is roughly 50,000 times normal atmospheric pressure.
Step 3: The Metal Catalyst Does Its Job
The metal catalyst melts under these conditions and acts as a solvent. It dissolves the carbon source and transports carbon atoms to the diamond seed, where they crystallise into diamond structure.
Step 4: Cooling and Recovery
The press slowly cools. The diamond crystal that formed around the seed is extracted, then cut, polished, and sent for certification.
One Additional Use of HPHT
Beyond growing diamonds from scratch, HPHT is also used to improve the colour of existing diamonds, both lab-grown and mined. A brownish diamond can be treated with HPHT to remove unwanted colour. This is a disclosed and accepted industry practice, and any reputable certificate will note it.
CVD vs HPHT: Key Differences at a Glance
- Process: CVD grows diamonds atom by atom using carbon gas. HPHT mimics earth conditions using extreme pressure and heat.
- Pressure: CVD runs at low, sub-atmospheric pressure. HPHT operates at 5 to 6 gigapascals, roughly 50,000 times normal air pressure.
- Temperature: CVD uses 700 to 1,000°C. HPHT requires 1,300 to 1,600°C.
- Carbon Source: CVD uses methane gas. HPHT uses graphite or carbon powder.
- Metal Catalyst: CVD does not need one. HPHT requires a metal catalyst, typically iron, nickel, or cobalt.
- Diamond Purity: CVD typically produces Type IIa diamonds, the purest form. HPHT most commonly produces Type Ib.
- Growth Time: CVD takes several weeks. HPHT is faster, often a few days to a couple of weeks.
- Common Use: CVD is the go-to for gem-quality jewellery diamonds. HPHT is used for both gem diamonds and colour treatment of existing stones.
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First Developed: CVD was refined through the 1980s and 1990s. HPHT dates back to 1954, when General Electric first successfully grew a synthetic diamond.
Does the Method Affect Quality?
This is the question most buyers actually want answered.
The short answer: both methods produce diamonds that can be graded across the full range of the 4Cs. You can find Internally Flawless, D-colour stones grown by both CVD and HPHT.
CVD diamonds can show graining or strain patterns under magnification. HPHT diamonds may show metallic flux inclusions from the catalyst in lower-quality stones. Neither affects the beauty or wearability of a well-graded stone.
What matters far more than the growth method is the cut quality and the 4Cs grade on the IGI certificate. A D-colour, VS1, Excellent-cut CVD diamond is a superb stone by any measure.
Can You Tell CVD from HPHT?
With the naked eye, no. Even with standard gemological tools, no. Distinguishing between the two requires advanced spectroscopy equipment, and even then it takes expert analysis.
Your IGI certificate will state the growth method if it has been identified. This is purely informational. It does not affect the diamond's value or quality grade.
Why Does This Matter for Indian Buyers?
India has a strong familiarity with diamond manufacturing. The country cuts and polishes over 90% of the world's diamonds by volume. Lab-grown diamond production is now growing rapidly here too, with Surat emerging as a major hub for CVD diamond manufacturing.
When you buy a lab-grown diamond from a certified Indian retailer, there is a real chance it was grown and polished entirely within India. That is a point of genuine pride, and it supports a domestic industry.
Frequently Asked Questions
Is CVD or HPHT Better for Jewellery?
Both produce gem-quality diamonds suitable for fine jewellery. CVD is more widely used for larger gem-quality stones today because of its purity output. HPHT remains common for smaller stones and colour treatment. Neither is universally superior.
Do CVD Diamonds Have the Same Hardness as Mined Diamonds?
Yes. Both CVD and HPHT diamonds score 10 on the Mohs hardness scale, identical to mined diamonds. Hardness comes from the crystal structure, which is the same in all three cases.
How Long Does It Take to Grow a Lab Diamond?
CVD growth typically takes two to four weeks for a gem-quality stone of one carat or more. HPHT can be faster, sometimes under two weeks for smaller stones.
Are CVD and HPHT Diamonds Certified by IGI in India?
Yes. IGI certifies both CVD and HPHT lab-grown diamonds using the same 4Cs system applied to mined diamonds.
Does the Growth Method Affect the Price?
There can be slight price differences between CVD and HPHT for comparable grades, but the gap is not significant. The 4Cs grade, particularly cut and clarity, has far greater influence on the final price than the growth method.
Can HPHT Treatment Change a Diamond's Colour Permanently?
Yes. HPHT colour treatment produces a permanent colour change and is an accepted industry process. It must be disclosed on the grading certificate, and any reputable seller will disclose it.
The Bottom Line
CVD and HPHT are two different answers to the same question: how do you recreate, under controlled conditions, what the earth does over billions of years?
Both answers work. Both produce diamonds that are chemically, structurally, and optically identical to mined diamonds. The method is a manufacturing detail. The result is a real diamond.
Next time someone tells you lab-grown diamonds are "just made in a machine," you can explain that mined diamonds were also made under pressure. One just had a longer commute.
Still have doubts about whether lab-grown diamonds are genuinely real? Read our detailed guide on Are Lab-Grown Diamonds Real? 10 Myths Busted by Goenka Jewellers for the full picture. Or browse Goenka Jewellers' lab-grown diamond collection and see certified CVD diamonds across rings, earrings, pendants, and more.