The short answer: scientists start with a tiny diamond seed, expose it to extreme heat and carbon, and grow a new diamond crystal atom by atom over several weeks. The result is chemically and physically identical to a diamond that spent billions of years forming underground.
The longer answer illuminates something worth understanding — because knowing how a lab grown diamond is made changes how you think about what you're buying.
It All Starts With a Diamond Seed
Whether the method is CVD or HPHT (more on both below), every lab grown diamond begins the same way: with a diamond seed — a thin slice of existing diamond crystal, typically less than a millimeter thick.
That seed is the structural foundation on which a new diamond grows. Carbon atoms are introduced under specific conditions, and they attach to the seed's crystal lattice, extending it layer by layer into a full gemstone. The seed provides the blueprint; the process provides the raw material and the energy to build it.
This is also why lab grown diamonds aren't "copies" of a specific diamond — the seed gives the crystal its starting structure, but the new growth develops its own unique characteristics: its own inclusions (or lack thereof), its own color, its own internal fingerprint.
Method 1: HPHT (High Pressure High Temperature)
HPHT is a method of growing diamonds by replicating the extreme heat and pressure found in the Earth's mantle — the same conditions responsible for forming natural diamonds over billions of years. A diamond seed is placed in a growth cell with a carbon source and subjected to intense heat and pressure until carbon crystallizes around the seed, building a new diamond.
HPHT is the older of the two methods, first successfully used to grow gem-quality diamonds in the 1950s.
Here's how it works:
A diamond seed is placed inside a growth cell alongside a carbon source (typically graphite or a compressed carbon powder) and a metal flux catalyst — usually iron, nickel, or cobalt. The entire assembly is then compressed inside a large hydraulic press and subjected to:
- Temperature: approximately 1,400–1,600°C
- Pressure: 5–6 GPa — that's roughly 50,000 to 60,000 times normal atmospheric pressure, or about 725,000 pounds per square inch
Under these conditions, the carbon material dissolves into the molten metal flux and begins to migrate toward the cooler diamond seed, where it crystallizes. The diamond grows outward from the seed, layer by layer. A typical HPHT cycle runs for 2–4 weeks to produce a rough diamond of gemstone quality.
What to know about HPHT diamonds:
- They tend to exhibit a cubic growth structure — the crystal grows outward in multiple directions
- They may contain trace metallic inclusions from the flux catalyst (iron, nickel, cobalt), which are generally not visible to the naked eye at normal clarity grades
- Modern colorless HPHT diamonds are typically Type IIa or Type IIb depending on trace boron levels in the growth chamber. Yellow or orange HPHT stones are usually Type Ib (isolated nitrogen), but these aren't what fine jewelry buyers are generally looking at
- Post-growth high-temperature annealing treatments can improve or modify color in some HPHT stones
HPHT is well-suited for producing larger rough crystals and is commonly used for industrial diamond production as well as gemstone-grade material.
Method 2: CVD (Chemical Vapor Deposition)
CVD is a method of growing diamonds by breaking down carbon-rich gas inside a vacuum chamber, allowing carbon atoms to deposit onto a diamond seed one layer at a time. It operates at lower temperatures and pressures than HPHT, gives producers more precise control over the growth environment, and consistently produces the purest type of diamond crystal — making it the dominant method for fine jewelry in the United States.
Here's how it works:
A diamond seed is placed inside a vacuum chamber, which is then sealed and filled with a carefully controlled mixture of gases — typically methane (CH₄) as the carbon source, combined with hydrogen. The chamber is heated to around 900–1,200°C, and microwave energy (or in some systems, a hot filament) ionizes the gas mixture into a plasma — a high-energy state where molecules break apart into atoms and ions.
In this plasma environment, carbon atoms detach from the methane molecules and descend onto the surface of the diamond seed. They attach to the crystal lattice one atom at a time, slowly building up a new diamond layer by layer. The process runs continuously for 2–4 weeks for gem-quality stones.
What to know about CVD diamonds:
- They grow in a layered, columnar pattern — building upward from the seed in flat plates
- CVD diamonds are almost universally Type IIa — the chemically purest classification of diamond, with essentially no nitrogen
- Type IIa is rare in nature (only about 1–2% of mined diamonds), but routine in CVD production
- This purity is why CVD diamonds consistently achieve D, E, and F (colorless) grades more reliably than mined diamonds
- CVD rough sometimes has a brown tinge from lattice strain during growth — this can usually be removed with a short post-growth HPHT treatment without affecting the stone's chemical identity
CVD's precision and controllability make it the preferred method for high-clarity, high-color stones used in fine jewelry.
CVD vs. HPHT: How Do They Compare?
Both methods produce real diamonds. The choice between them affects the stone's characteristics, not its authenticity. Here's a side-by-side view:
| HPHT | CVD | |
|---|---|---|
| Temperature | 1,400–1,600°C | 900–1,200°C |
| Pressure | ~50,000–60,000 atm | Near atmospheric |
| Growth time | 2–4 weeks | 2–4 weeks |
| Diamond type | Type IIa or IIb (colorless); Type Ib (yellow/orange) | Almost always Type IIa |
| Typical color | Historically variable; modern colorless HPHT stones are now competitive with CVD | Consistently D–F colorless; may require brief post-growth treatment to correct brown tinge |
| Possible inclusions | Metallic flux traces | Graphite, strain patterns, striations |
| Market dominance | Dominant in China; widely used globally | Preferred for US fine jewelry |
| Well-suited for | Both colorless and fancy colored diamonds | High-clarity, high-color colorless fine jewelry |
Both methods produce certified, real diamonds. The distinction matters not because one is fake and one is real, but because each has different quality characteristics worth understanding before you buy. CVD has become the preferred method for colorless fine jewelry in the United States — and there are real reasons for that — but well-grown HPHT diamonds are genuinely competitive at the quality level that matters.
From Rough Crystal to Finished Diamond
Growing the rough diamond is only the beginning. Once removed from the growth chamber, a lab grown diamond rough goes through exactly the same process as a mined rough diamond:
1. Evaluation and planning. The rough crystal is analyzed to map its internal structure, inclusions, and optimal yield. A cutter determines the best way to shape it for maximum beauty and value.
2. Cleaving or sawing. The rough is cut into workable pieces using lasers or diamond-tipped blades.
3. Bruting. Two rough diamonds are spun against each other to shape them into a rounded, cone-like form — establishing the basic shape of the future stone.
4. Faceting. A skilled cutter polishes the diamond on a rotating wheel embedded with diamond dust, creating the precise geometric facets that determine how the stone interacts with light. This is the step that turns a rough crystal into something that sparkles.
5. Final polishing and quality check. The finished stone is inspected, cleaned, and prepared for grading.
6. Certification. The diamond is sent to an independent gemological laboratory — IGI, GIA, or another accredited body — for grading on the Four Cs (cut, color, clarity, and carat weight).
Every step after the growth chamber is identical to what happens with a mined diamond. The equipment is the same. The skills are the same. The resulting certificate is evaluated on the same scale.
The Purity Advantage, Explained
One of the more counterintuitive facts about lab grown diamonds: the controlled CVD growth environment often produces chemically purer stones than nature does.
About 98% of mined diamonds trap nitrogen clusters in their crystal structure during formation — what gemologists call Type Ia — responsible for the warmth in color at lower grades (Gemological Institute of America). CVD diamonds form in a nitrogen-controlled environment, producing Type IIa stones with essentially no nitrogen. Only about 1–2% of natural diamonds reach Type IIa; CVD produces it routinely.
This is why CVD diamonds so consistently achieve D, E, and F colorless grades — not because of a special treatment, but because the growth conditions exclude the impurities that cause tinting in the first place. HPHT colorless diamonds are also generally low in nitrogen, achieving Type IIa or IIb classification, though the production environment is less inherently controlled on this point than CVD.
Why CVD Has Become the Industry Standard for Fine Jewelry
The fine jewelry market has moved toward CVD — and it's not arbitrary. Several practical advantages have made it the dominant choice for high-quality colorless diamonds, particularly in the United States:
Smaller, more scalable equipment. HPHT requires massive hydraulic presses that take up significant floor space and are expensive to operate. CVD reactors are compact enough that a single facility can run hundreds of chambers simultaneously. This scalability has driven production costs down and quality consistency up.
Better color control. Because the CVD growth environment is tightly controlled and nitrogen is deliberately excluded, CVD diamonds more reliably achieve D, E, and F colorless grades. HPHT diamonds form in the presence of nitrogen from the surrounding atmosphere (which is 78% nitrogen), which historically produced an orangey-yellow tint. Modern HPHT operators use nitrogen suppressants to counter this, but CVD's environment is inherently cleaner for colorless production.
Type IIa purity. Over 70% of CVD diamonds achieve Type IIa classification — the chemically purest form of diamond, with essentially no nitrogen. This is the same category as some of the world's most prized natural diamonds. Only 1–2% of mined diamonds ever reach it naturally.
Where HPHT still shines: HPHT remains the preferred method for fancy colored lab grown diamonds (yellow, blue), for industrial applications requiring extreme hardness, and is still widely used by producers in China at scale. It also remains the method used to treat many CVD diamonds post-growth to improve color — so the two methods are often complementary rather than competing.
The bottom line: if you're buying a colorless fine jewelry diamond, CVD is what the industry predominantly uses and recommends. Your certificate will state the growth method — and if it says CVD, that's a good sign you're getting a stone grown with the fine jewelry buyer in mind.
What to Look For When Buying a Lab Grown Diamond
Not all lab grown diamonds are equal — and this is where understanding the growth process pays off as a buyer. Both CVD and HPHT can produce excellent stones, but both can also produce problematic ones when growers cut corners or rush production.
In CVD diamonds: three things to watch for
Brown is caused by two main things: empty voids in the diamond crystal structure and nitrogen atoms trapped during growth. Brown hues in CVD diamonds can range in intensity and sometimes have gray or pink undertones. The root cause is almost always a growth environment that ran too fast or wasn't properly controlled. A reputable grower running their reactor at the right pace produces clean, colorless material — many CVD diamonds actually undergo a brief post-growth HPHT treatment to correct any residual brown tint, which is standard practice and doesn't affect quality.
Gray in CVD diamonds is caused by three things: silicon vacancy defects (silicon from the reactor's quartz window burning off and entering the chamber when temperatures run too high), graphitic nanoclusters (carbon forming as graphite instead of diamond when the machine runs too fast), and boron compensating for nitrogen. The critical phrase from gemologists is: the faster you grow a CVD diamond, the more that can go wrong. Gray tinge can appear even in D-color diamonds, making it particularly important to view stones in various lighting conditions.
Strain looks like streaks on glass — a blurriness or cloudiness in the crystal surface caused by edge dislocations during carbon deposit. The most common cause is low-quality or overused diamond seeds. Seeds degrade after each use and are expensive to replace. Some growers reuse seeds well past their optimal condition to save money, which introduces strain patterns into the finished diamond. A diamond grown from a fresh, high-quality seed will be free of strain; one grown from a degraded seed may show streaking that affects its luster.
Striations are a related CVD-specific issue: rings inside the diamond caused by stopping and restarting the reactor during the growth cycle. The more times the reactor is stopped and restarted, the more rings accumulate. A diamond with 8 or more growth cycles will typically show heavy striation — appearing out of focus or lacking the sharp brilliance of a well-grown stone. When shopping, look for diamonds that appear crisp and bright under magnification, not hazy or ringed.
In HPHT diamonds: three things to watch for
Blue/Blue-Gray is caused by HPHT diamonds' exposure to the nitrogen-rich atmosphere during growth. To counteract the resulting yellow-orange tint, growers sometimes add boron or use specific metal gasket elements — but too much can introduce a blue-gray hue that dulls sparkle.
Gray in HPHT stones can result from aluminum, titanium, or other trace elements within the crystal structure, or from irradiated blue tones that shift to gray over time.
Phosphorescence — a hazy or milky appearance under low light that can persist for several minutes — is caused by boron. It isn't necessarily visible on a certificate but becomes apparent in dim restaurant lighting or candlelight. This is worth specifically checking if you're buying an HPHT diamond.
The practical buying checklist
When evaluating any lab grown diamond, regardless of growth method:
- Always buy certified — IGI or GIA certification provides an independent assessment of quality and discloses the growth method on the report
- View the stone in multiple lighting conditions, not just bright overhead light where everything looks good
- Prioritize Excellent or Ideal cut — this is the one quality factor that most directly determines how much a diamond sparkles, and it's non-negotiable at the quality level we carry
- F color or better for true colorlessness — this matters more at larger carat sizes where warmth or tint becomes more visible to the eye
- VS clarity or better for stones that are visually clean without requiring a microscope to confirm it
- Ask about the growth process — a knowledgeable seller should be able to tell you whether the diamond is CVD or HPHT and what that means for the stone you're looking at
For a full explanation of how the 4Cs work together in practice, see our Diamond Education: The 4Cs guide.
At LabGrownDiamonds.com, every stone we carry meets a minimum standard of F+ color, VS+ clarity, and Excellent/Ideal cut — whether it's going into a pair of stud earrings, an engagement ring, or any piece in our fine jewelry collection.
Why Does the Process Matter to You as a Buyer?
Understanding how lab grown diamonds are made helps you understand a few practical things:
Inclusions are normal — but type matters. Just as mined diamonds have inclusions, lab grown diamonds can too. The types are different depending on method: metallic traces in HPHT, graphitic marks or strain patterns in CVD. A VS1 or VS2 graded stone is visually clean regardless of origin, but understanding what to look for helps you evaluate what you're buying.
CVD is generally preferred for fine jewelry. For colorless diamonds — the kind used in engagement rings, studs, and fine jewelry — CVD's controlled growth environment produces more consistent color and purity. That's why it now dominates the US fine jewelry market.
The timeline is compressed, not the quality. Growing a diamond in weeks rather than billions of years doesn't diminish it — it's the same fundamental process, accelerated through technology rather than geological time. The crystal structure that results is identical either way. What matters is whether the grower took the time to do it right.
What you end up with is a stone that sparkles like a diamond, tests like a diamond, and grades like a diamond — because, by every scientific and legal measure, it is one.
How Long Does It Take to Grow a Lab Diamond?
A common question — and the answer is more nuanced than "a few weeks."
The growth phase itself — the time a diamond crystal spends actively forming inside a HPHT press or CVD chamber — typically runs 2 to 4 weeks for gem-quality stones. Larger diamonds or those targeting very specific quality parameters can take longer.
But the full journey from seed to finished, certified stone takes considerably longer when you factor in the additional steps: post-growth treatment (some CVD diamonds require a brief HPHT annealing process to correct color), cutting and faceting by skilled artisans, final polishing and inspection, and certification by an independent gemological laboratory. From start to certified finished stone, the realistic timeline is typically 8 to 12 weeks for most jewelry-quality diamonds.
By comparison, natural diamonds form over 1 to 3 billion years. The lab process doesn't produce an inferior diamond — it produces the same diamond on a radically different timeline.
Frequently Asked Questions
How are lab grown diamonds different from mined diamonds? The only difference is origin and formation time. Lab grown diamonds form in a controlled laboratory environment over weeks; mined diamonds form underground over billions of years. The resulting chemical composition, crystal structure, hardness, brilliance, and optical properties are identical.
Which is better — CVD or HPHT lab grown diamonds? For colorless fine jewelry diamonds, CVD has become the industry-preferred method — and there are real reasons why. CVD's controlled growth environment excludes nitrogen, producing Type IIa purity and D–F colorless grades more consistently. It also uses smaller, more scalable equipment, which has improved quality control as the technology matured. HPHT remains excellent for colored diamonds and industrial applications, and is still widely used globally. Both methods produce certified, real diamonds — but if you're buying a colorless stone for jewelry, CVD is what most reputable producers and retailers work with.
Do lab grown diamonds have inclusions? Yes — just like mined diamonds. The types of inclusions differ slightly (metallic traces in HPHT, graphitic marks in CVD), but a VS1 or VS2 graded lab grown diamond is visually clean to the naked eye, the same as a mined stone at the same grade.
Can a lab grown diamond be certified? Yes. Lab grown diamonds are certified by the same independent gemological laboratories that certify mined diamonds — primarily IGI and GIA — and graded using the same Four Cs (cut, color, clarity, carat weight).
Are lab grown diamonds made of the same material as natural diamonds? Yes. Both are pure carbon arranged in a cubic crystal lattice — the precise chemical and structural definition of a diamond. The material is identical regardless of where or how it formed.
Continue learning: What Is a Lab Grown Diamond? | Are Lab Grown Diamonds Real? | Lab Grown vs. Natural Diamond
