How Are Laboratory Diamonds Made? HPHT vs CVD Explained

The lab versus mined diamond decision sits at the centre of nearly every engagement ring conversation we have today. It's no longer a niche question — it's the question.

Laboratory grown diamonds have become a genuine contender for most couples searching for the perfect engagement ring, or any fine diamond jewellery for that matter.

I hope this post gives you a rich view of how lab diamonds are actually made, and makes one thing unmistakably clear: regardless of origin, every process we'll discuss yields real, true diamonds in every sense of the word. Not simulated. Not imitation. Diamond.

Laboratory grown diamonds in a nutshell

Lab-grown diamonds — also referred to as laboratory-made diamonds, lab diamonds, man-made diamonds, or cultured diamonds — are as real as any diamond ever pulled from the Earth.

They're made in controlled laboratory environments that mimic and dramatically accelerate the natural diamond formation process, compressing what takes millions of years underground into a matter of months.

Using the same raw ingredient the Earth's mantle has always used — carbon — this process yields true diamonds with the same crystal structure, the same sparkle, fire, and hardness that diamonds have always been prized for.

They're 100% real diamonds. Full stop.

How does mother nature make diamonds?

Mother Earth has been running the same recipe for hundreds of millions of years:

Naturally occurring carbon + extreme pressure + intense heat = crystallised carbon (diamond).

Diamonds formed at depths of up to 150km beneath the Earth's surface, where carbon found itself under pressures as high as 50,000 atmospheres and temperatures reaching 1,100°C. Under those conditions, it had nowhere to go but to crystallise. Over aeons, volcanic activity pushed these crystals upward toward the surface — where, eventually, we found them.

First to the Party: High Pressure, High Temperature (HPHT)

The race to create a diamond in a laboratory started in the early 1940s, though the war had other plans. It wasn't until 1958 that scientists at General Electric crossed the finish line — successfully crystallising carbon into diamond inside a controlled chamber using immense pressure and heat.

In what I can only imagine was a refreshingly short meeting, GE named the process exactly what it was: High Pressure, High Temperature. HPHT.

The mechanics are elegant in their logic. A tiny diamond — called a seed — is placed at the centre of a carbon-filled chamber. Pressure climbs to around 100,000 atmospheres and temperatures reach 2,000°C. The carbon melts and crystallises around the seed, growing it into a larger diamond. Unlike CVD, HPHT works fast — the phase conversion from graphite to diamond happens in days rather than weeks, making it the more efficient of the two processes for larger stones.

Fun fact: the largest IGI-certified lab-grown diamond on record is a 75.33 carat emerald-cut stone — grown in India using CVD, ironically, not HPHT.

And Then There Was CVD: Chemical Vapour Deposition

A few decades later, a second method arrived. CVD takes a different route to the same destination.

A seed diamond — often one grown by HPHT — is placed inside a chamber filled with carbon-rich gas. That gas is ionised into plasma using technology not unlike lasers and microwaves, breaking down its molecular bonds. Pure carbon then rains down inside the chamber, settling and crystallising layer by layer onto the seed. The process typically takes two to six weeks, longer for larger stones.

It sounds more like science fiction than the brute-force logic of HPHT. And in many ways it is more technologically sophisticated. That said, HPHT remains the preferred method for growing gem-quality diamonds destined for fine jewellery — producing superior crystal uniformity, particularly in stones above 3 carats. 

It's also worth noting that manufacturers have refined both processes dramatically over the past decade; today, more than 90% of HPHT-grown diamonds submitted to GIA grade as colourless — something that was virtually impossible fifteen years ago.

From Rough Crystal to the Gem You Fall in Love With

Once the carbon has crystallised — whether deep underground over millions of years or inside a laboratory chamber over a few weeks — the journey from rough crystal to finished diamond follows exactly the same path. The origin becomes irrelevant. What matters now is the craft.

Step One: Planning

Rough diamonds, whether mined or lab-grown, arrive in all shapes and sizes — and rarely cooperative ones. Maximising what you get out of each piece of rough is both a science and an art.

Each rough stone is 3D scanned using advanced imaging technology. Software analyses the internal structure, maps existing inclusions, and models thousands of potential cutting configurations. Technicians then determine the optimal shape and carat yield — balancing size, clarity, and the geometry needed to unlock the stone's brilliance.

Once the plan is locked, the intended shape is marked by laser and the stone moves to the next stage.

Step Two: Cutting and Polishing

The rough diamond is first cut using high-powered lasers, following the blueprint established during planning with extraordinary precision.

From there it passes to a diamond cutter — a craftsperson whose skill and patience is, frankly, underappreciated. Working under magnification, they facet and polish each surface by hand, coaxing out the fire and brilliance that makes a diamond what it is.

It's worth pausing on this: the sparkle you see in a finished diamond isn't just a property of the stone. It's the result of someone's hands and eyes and years of experience, applied one facet at a time.

The Final Step: Grading

Once a diamond leaves the polisher's hands, it enters the last and arguably most important stage of its journey — independent grading.

Each stone is individually packed and sent to an accredited gemological laboratory, where trained gemologists assess it across the four characteristics that define a diamond's quality and value: cut, colour, clarity, and carat weight. If you want a deeper understanding of how these factors interact, we've written a full guide to the 4Cs of laboratory grown diamonds.

The results are documented in a grading report — a stone's fingerprint, essentially — detailing every measurable characteristic. The diamond is then repackaged with its certificate and returned to the manufacturer, from where it works its way down the supply chain to jewellers like us, and eventually to you.

GIA and IGI: The Two Names That Matter

The GIA — Gemological Institute of America — has long been the most trusted grading authority for mined diamonds, and remains the benchmark the industry measures itself against.

For laboratory grown diamonds, the IGI has taken a clear lead. This isn't a compromise. IGI grading is rigorous, internationally recognised, and in our experience holds up comfortably alongside GIA standards. The practical reality is that with lab diamonds trading at a significant discount to mined stones, IGI's more accessible grading fees make commercial sense without any sacrifice in credibility or consistency.

One important note: a diamond's origin is always clearly disclosed on the grading report. There is no ambiguity, no grey area. A GIA or IGI certificate will explicitly state whether the stone is laboratory-grown or mined — so you always know exactly what you're buying, documented by an independent third party.

At Poggenpoel, we work with both. Either certificate gives you a complete, reliable, independently verified record of exactly what you're buying.

Same, Same?

In every way that matters, yes.

The line separating a laboratory-grown diamond from a mined one is paper-thin — a difference of origin, not of substance. The carbon is identical. The crystal structure is identical. The sparkle, the hardness, the fire — identical. What differs is the journey, and increasingly, the price.

The future for lab-grown diamonds is bright, and if you're starting your engagement ring search, they're absolutely worth serious consideration.

If you have any questions about lab-grown diamonds, the differences between HPHT and CVD, or anything else covered here — our studios in Pretoria, Sandton, and Cape Town are always open for a conversation. You're also welcome to reach out directly at johan@poggenpoel.com.

Take care,

Johan Poggenpoel

Owner, Poggenpoel Diamond Jewellers

www.poggenpoel.com