If you’re considering a lab-grown diamond for your engagement ring, you’ve probably asked the question: how are lab-grown diamonds made? It’s a fair thing to wonder. These stones look identical to mined diamonds, they test as real diamonds, and they cost significantly less, so what’s actually happening behind the scenes to create them?

The short answer: scientists recreate the extreme conditions found deep within the Earth, either through intense heat and pressure or by growing diamond crystal from a carbon-rich gas. The two methods, HPHT (High Pressure High Temperature) and CVD (Chemical Vapour Deposition), each produce genuine diamonds with the same physical, chemical, and optical properties as their natural counterparts. But the processes themselves are quite different in how they work.

At A Star Diamonds, we offer both natural and lab-grown diamonds across our bespoke engagement rings and wedding bands. Our gemologists in Hatton Garden work with clients every day who want to understand exactly what they’re buying, and that starts with knowing how these stones are made. This guide breaks down both methods in plain terms, so you can walk into that decision with clarity and confidence.

Why lab-grown diamond methods matter

When you start researching how are lab-grown diamonds made, you quickly realise the method isn’t just a technical detail locked away in a laboratory. The production process directly influences the diamond’s colour characteristics, how it responds to light, and whether it needs any post-growth treatment before it reaches a jeweller. Understanding the difference between CVD and HPHT helps you make a far more informed buying decision, because it shapes what you’re actually getting for your money.

The method used to grow a diamond can affect its colour grade, clarity, and whether any treatment was applied after growth.

The method affects more than just the price

Most people assume the main reason to care about production methods is cost. Price is relevant, yes, but it’s not the whole picture. The HPHT and CVD processes produce diamonds with subtly different growth characteristics, which trained gemologists can identify under magnification. Inclusions, strain patterns, and fluorescence can all vary depending on which method was used, and these factors feed directly into how the stone is graded and valued by independent certification bodies such as the Gemological Institute of America (GIA).

Reputable certification reports will state which growth method was used. This matters when you’re comparing two stones at a similar price point, because a certified stone with a clearly documented origin gives you verifiable information rather than a sales pitch. If a retailer cannot tell you which process produced the diamond they’re offering, that detail is worth noting before you commit to a purchase.

What "real diamond" actually means

Lab-grown diamonds are chemically and structurally identical to mined diamonds. Both consist of carbon atoms arranged in the same crystal lattice structure, which is what gives diamonds their hardness and optical brilliance. Whether a diamond formed over billions of years under the Earth’s mantle or over a few weeks in a controlled growth chamber, the result is the same material. A standard diamond tester cannot distinguish between the two, and neither can the naked eye.

This distinction is worth stating clearly, because some buyers arrive with the misconception that lab-grown diamonds are somehow synthetic in the way that cubic zirconia or moissanite are. Those stones have entirely different chemical compositions and behave differently under light. A lab-grown diamond is simply a diamond grown in a different environment, not a diamond substitute. The science behind both CVD and HPHT was developed specifically to replicate natural diamond formation with precision, and the resulting stones carry the same 4Cs grading scale and physical properties you would expect from any diamond in a jeweller’s cabinet.

How the CVD process grows a diamond

Chemical Vapour Deposition, or CVD, is one of the most widely used answers to how are lab-grown diamonds made, and the process is more straightforward than its name suggests. A thin slice of existing diamond, known as a seed crystal, is placed inside a sealed chamber. That chamber is then filled with a carbon-rich gas, typically methane, and heated to temperatures of around 700 to 1,200 degrees Celsius. At those temperatures, the gas breaks apart and pure carbon atoms fall onto the seed crystal, gradually building up layer by layer into a full-sized diamond over a period of weeks.

CVD diamonds grow from the top down, one atomic layer at a time, which gives gemologists a recognisable layered growth pattern under magnification.

What happens inside the growth chamber

The chamber itself uses microwave energy or a similar energy source to ionise the gas, creating what scientists call a plasma cloud. That plasma strips the hydrogen away from the methane, leaving free carbon atoms available to bond with the diamond seed below. The process is slow and controlled, which is precisely what makes it attractive for producing high-clarity stones with relatively predictable characteristics.

What CVD diamonds look like after growth

When the CVD diamond finishes growing, it typically has a brownish or greyish tint caused by structural defects that develop during the layered growth process. This means most CVD stones go through a post-growth treatment, usually an HPHT treatment, to remove that colour and bring the stone up to a near-colourless or colourless grade. This treatment is not a flaw and is standard practice in the industry, but a reputable certification report from a body such as the GIA will disclose it clearly. When you buy a CVD diamond, checking for that documentation tells you exactly what you have.

How the HPHT process grows a diamond

High Pressure High Temperature, or HPHT, is the older of the two methods for how are lab-grown diamonds made, and it takes its cue directly from nature. Deep within the Earth’s mantle, natural diamonds form under pressures of around 725,000 pounds per square inch and temperatures exceeding 1,300 degrees Celsius. HPHT replicates those exact conditions inside a growth press, using a small diamond seed, a carbon source such as graphite, and a metal catalyst like iron or cobalt to trigger crystal formation.

HPHT was the first commercially viable method for producing gem-quality diamonds in a laboratory setting, developed in the 1950s.

What happens inside an HPHT press

Three main press designs exist in the industry: the belt press, the cubic press, and the split-sphere press. Each design applies enormous mechanical force from multiple directions to a small chamber containing the diamond seed and its surrounding carbon material. As temperature climbs, the metal catalyst dissolves the graphite and carbon atoms migrate toward the cooler seed crystal, bonding to it and building outward into a larger stone over a period of days to weeks.

Stones that emerge from an HPHT press tend to grow in a cuboctahedral shape, which is a recognisable marker for gemologists examining growth patterns under magnification. Nitrogen is commonly present during HPHT growth, which can introduce a yellow or brownish tint depending on concentration levels. Higher-quality HPHT diamonds are grown under carefully controlled conditions to minimise nitrogen uptake and produce a near-colourless result.

HPHT as a treatment for existing diamonds

HPHT is not only a growth method. Manufacturers also apply it as a post-growth treatment to CVD diamonds and certain natural diamonds to improve their colour grade. When a stone carries the label HPHT-treated rather than HPHT-grown, that distinction has real significance for how the stone is graded and valued.

A proper certification report from a body such as the GIA will state this clearly, so always check the certificate before you commit to a purchase.

CVD vs HPHT: quality, colour and treatments

When buyers ask how are lab-grown diamonds made, they often want to know which method produces the better stone. The honest answer is that neither method is universally superior. Both CVD and HPHT can produce excellent diamonds, but each has predictable tendencies around colour and clarity that are worth understanding before you start comparing stones at a jeweller.

Colour tendencies by method

CVD diamonds commonly start with a brown or grey tint after the growth process completes. That colour comes from structural irregularities that develop as carbon layers build up, and manufacturers typically correct it using a follow-up HPHT treatment before the stone reaches a jeweller. HPHT-grown diamonds, by contrast, can carry a yellow tint if nitrogen levels during growth are not carefully managed. High-quality HPHT stones grown under tightly controlled conditions often achieve very clean colour grades without any additional treatment.

The colour grade on a certified diamond reflects both the growth method and any post-growth treatment applied, so always read the full grading report rather than the headline figure.

Post-growth treatments and what they mean for you

Post-growth treatment is a standard and widely accepted practice across the lab-grown diamond industry. A CVD diamond that has been HPHT-treated afterwards is not a lesser stone. It simply went through an extra step to reach its final colour grade. What matters is full disclosure on the certificate: a report from a recognised grading body such as the GIA or IGI will state both the growth method and whether any treatment was applied, giving you the complete picture in one document.

Comparing two stones at a similar price becomes far easier when you check the certificate for treatment history before making any decisions. A diamond graded D colour because it grew at that grade and one that reached D after treatment are both genuine diamonds with identical physical properties. Understanding that difference simply makes you a more informed buyer, which is exactly where you want to be when spending a significant amount on a stone you’ll wear every day.

How to check certification and buy with confidence

Understanding how are lab-grown diamonds made is only half the work. The other half is knowing how to verify what you’re buying before you hand over your money. A grading report from a recognised certification body is the single most important document you can request when buying a lab-grown diamond, because it records everything from the growth method to any post-growth treatments applied to the stone.

What to look for on a grading report

The two most widely recognised bodies for grading lab-grown diamonds are the Gemological Institute of America (GIA) and the International Gemological Institute (IGI). Both issue detailed reports that list the stone’s 4Cs (cut, colour, clarity, and carat weight), its growth method (CVD or HPHT), and any treatments it received after growth. When you review a certificate, check that all four of these elements are present and clearly stated.

A certificate that omits the growth method or treatment history is incomplete, and that gap is reason enough to ask more questions before proceeding.

If a retailer cannot produce a certificate or pushes back when you ask for one, treat that as a clear warning sign. No reputable jeweller will hesitate to provide grading documentation for a stone they’re confident selling.

Questions to ask before you buy

Before committing to a purchase, ask your jeweller directly which growth method produced the stone and whether any post-growth treatment was applied. A straightforward answer, backed by a certificate, is what you’re looking for. You should also confirm that the certificate number is laser-inscribed on the diamond’s girdle, which lets you match the physical stone to its paperwork and rule out any substitution.

At A Star Diamonds, our gemologists in Hatton Garden walk you through every detail of the certification before you make any decisions, so you leave the appointment knowing exactly what you are buying and why.

Quick recap

Now you know how are lab-grown diamonds made, the key points come down to two methods and one crucial document. CVD grows a diamond layer by layer from a carbon-rich gas, while HPHT replicates the intense pressure and heat found deep in the Earth’s mantle. Both produce genuine diamonds with the same chemical structure, hardness, and optical properties as mined stones, so neither method produces a lesser stone.

Post-growth treatments are standard and not a concern, provided your certificate discloses them clearly. Always check that your grading report lists the growth method and any treatment history, and confirm the certificate number is laser-inscribed on the stone’s girdle. A reputable jeweller will answer those questions directly and back every answer with documentation.

Ready to choose a lab-grown diamond for your engagement ring? Book a consultation with A Star Diamonds and our Hatton Garden gemologists will walk you through every option and certification detail until you feel completely confident.