Not every lab grown diamond is made the same way. Two different processes, CVD and HPHT, both produce genuine diamonds with the same chemical, physical and optical properties as a mined stone. The growth chamber behind a diamond rarely tells you what you actually need to know before buying one. What matters more is what each process is suited to, and what that means for the specific stone in front of you.
This piece looks at the types of lab grown diamonds from the buyer's side: what each is good for, and which suits which priority. It also covers what's worth asking a jeweller before choosing a stone. For the full mechanics behind how each diamond is grown, from gas chambers to press machines to growth timelines, How Lab Grown Diamonds Are Made covers that ground properly. If you're new to lab grown diamonds altogether, our explainer on what lab grown diamonds are covers the basics first.
Origin and Composition Are Two Separate Questions
It's easy to conflate these, so it's worth separating them upfront. Origin is about how a diamond formed: lab grown or mined, and if lab grown, CVD or HPHT. Composition is about purity, based on how much nitrogen a diamond carries:
- Type I: contains measurable nitrogen
- Type II: contains little to none
- Type IIA: the rarest and most colourless classification, roughly 1-2% of all diamonds regardless of origin
These two systems don't determine each other. A CVD diamond can be Type I or Type IIA. So can an HPHT diamond. Growth method and purity classification are answered by different parts of the same certificate, not by one another.
CVD and HPHT, in Brief
CVD grows a diamond seed inside a vacuum chamber filled with carbon-rich gas, building the crystal up gradually, layer by layer, over two to four weeks. That slow, closely controlled environment is why CVD tends to produce diamonds well suited to reaching Type IIA purity, and it's the method COSMOS works with exclusively.
HPHT grows a diamond seed under extreme heat and pressure in a press, closer in principle to how diamonds form naturally underground, and does it in days rather than weeks. HPHT also has a second role elsewhere in the industry: treating and improving the colour of diamonds that already exist, whether they were grown by CVD or mined. That dual role, growing new stones and treating existing ones, is the detail buyers most often miss.
What Each Method Actually Suits
- Prioritising the highest colourless clarity: CVD offers more consistent control over the growth environment and is more likely to reach Type IIA, the classification COSMOS builds its collection around.
- Buying a stone that's had its colour improved after growth: that's HPHT treatment at work, not a growth method in this instance. A treated stone and an as-grown stone are different purchases even when both are genuine diamond, so it's worth knowing which one is in front of you.
- Not especially concerned with growth method: a reasonable position to take. In that case, the certification and grading report behind the specific stone matter more than whether it started life in a chamber or a press.
Neither Method Makes a Lesser Diamond
CVD and HPHT both produce real diamond: the same carbon structure, the same hardness, the same optical properties as a mined stone. Neither is a simulant, which puts both firmly in a different category from cubic zirconia or moissanite, materials that aren't diamond at all regardless of how they're shaped or sold. The growth method changes how the carbon came together. It doesn't change what the finished stone is.
What to Ask Your Jeweller
Before buying, it's worth asking directly:
- Which independent lab issued the certificate, and can I see the full report
- Is this diamond as grown, or has it been treated after growth
- What type classification does it fall under, and is Type IIA confirmed if that's a priority
- Does the certificate confirm lab grown origin specifically, not just the 4Cs
A jeweller who can answer all four plainly is selling you a properly documented stone, regardless of which process grew it. One who can't is worth a second question or two before you commit.
Buying With the Right Questions
Choosing between CVD and HPHT was never really the decision that mattered. What matters is the specific stone in front of you. Is it properly graded, honestly represented, and backed by an independent certificate stating exactly what it is: treated or as grown, Type I or Type IIA, lab grown and confirmed as such. Ask those questions of a jeweller before asking which process grew the diamond, and the growth method tends to sort itself out.
Every COSMOS diamond is grown using CVD from Type IIA seeds, finished without post-growth treatment, and independently certified. There's nothing on that list above that isn't already answered before you ask. Browse the Cosmos Lab Grown Diamonds collection to see it for yourself, or read more about the brand's approach on the about page.
FAQs
Should I choose a CVD or HPHT lab grown diamond?
Between the two main types of lab grown diamonds, neither is categorically better. CVD tends to suit buyers prioritising the highest clarity and colour, while HPHT is efficient for growth and also used to treat existing stones. The certification behind the specific diamond matters more than the method.
Does it matter which method grew my diamond?
Only to the extent it affects the type of stone you end up with. Both produce genuine diamond, so the more useful question is what the grading report says, not which chamber it came from.
How do I know if a diamond has been treated after growing?
Ask directly, and check the certificate. An independent lab report will state whether a stone is as grown or has undergone post-growth treatment such as HPHT colour enhancement.
What certification should I ask for when buying a lab grown diamond?
A report from a recognised independent lab that confirms lab grown origin, the 4Cs, and whether any treatment has been applied. IGI certification covers all of this for COSMOS diamonds.
Is a Type IIA diamond worth choosing over other types?
If colourless clarity is the priority, yes, it's the rarest and purest classification available. If budget or carat size matters more, a well-graded Type I or II diamond is still a genuine, high-quality choice.
Can I trust a jeweller who doesn't know the growth method of their own stock?
Worth being cautious. A jeweller working with certified lab grown diamonds should be able to speak to growth method, type classification, and treatment history without hesitation. All of it sits on the certificate they're meant to be selling alongside the stone.
