Lab‑grown diamonds are real diamonds crystallised from pure carbon in a controlled environment. Using advanced equipment to recreate either extreme heat and pressure (HPHT) or a carbon‑rich plasma (CVD), technicians grow diamond crystals in weeks rather than geological time. Chemically, physically and optically they match mined diamonds; the difference is origin, not substance.

This guide explains how diamonds form in nature versus a lab, the pivotal role of diamond seeds, and the step‑by‑step HPHT and CVD processes with typical timeframes. You’ll find a clear comparison of the two methods, post‑growth treatments and colour engineering, and what happens next: cutting, polishing and grading. We’ll cover growth durations, quality factors to check, how certification and instruments confirm a diamond’s origin, and what to know about sustainability and pricing. Finally, we’ll answer common questions and help you choose the right option for your ring.

How diamonds form in nature vs in a lab

Deep in the Earth’s mantle, natural diamonds form 177–241 km below the surface where pressures approach 50,000 atmospheres and temperatures reach roughly 900–1,300°C. Over millions of years, carbon atoms lock into the diamond lattice, and ancient volcanic eruptions later ferry those crystals up in kimberlite pipes.

In a lab, the same result is achieved in weeks. HPHT recreates mantle‑like conditions, pressing a carbon source around a seed at about 1,300–1,600°C and extreme pressure. CVD grows diamond in a vacuum chamber, where a carbon‑rich plasma at roughly 800–900°C deposits carbon atom by atom onto a seed. Either way, how lab diamonds are made changes origin, not the diamond’s properties.

The role of diamond seeds

A diamond seed is a tiny piece of real diamond that acts as the template for crystal growth. It gives carbon atoms a perfect lattice to copy, so the new crystal grows predictably and with fewer defects. Both HPHT and CVD begin with a seed, and its orientation influences the direction and shape of the rough that forms.

In CVD, seeds are often thin plates roughly 300 microns thick and about 10×10 mm, typically sliced from an existing lab diamond, then meticulously cleaned so no imperfections propagate. In HPHT, a small seed sits within a carbon source and metal flux. Whether the seed is natural or lab-grown, the result is the same: a diamond. Seeds make how lab diamonds are made repeatable—and achievable in weeks.

HPHT diamonds: step-by-step process and timeframes

High Pressure High Temperature (HPHT) recreates mantle-like conditions to grow diamonds around a seed. A tiny diamond seed sits with a carbon source (commonly graphite) and a metal flux. Powerful presses apply extreme pressure while electric pulses raise temperatures to about 1,300–1,600°C. Carbon dissolves into the molten metal mix and then crystallises onto the seed. Depending on desired size and quality, growth runs for weeks; larger gem roughs often take around a month, and may contain minute metallic traces not visible to the eye.

1. Prepare the capsule: Place a diamond seed with carbon and a metal flux (e.g., iron–nickel–cobalt).
2. Apply pressure and heat: Use belt, cubic or split-sphere (BARS) presses; heat via electric pulses to ~1,300–1,600°C at very high pressure.
3. Dissolve and transport carbon: Carbon dissolves in the flux and precipitates onto the seed, building the crystal.
4. Stabilise and cool: Hold conditions for steady growth, then cool and release the rough crystal; tiny metal residues can remain.
5. Typical timeframes: Hours for very small crystals; gem-quality sizes generally take weeks—commonly 2–4 weeks, often about one month for larger stones.

CVD diamonds: step-by-step process and timeframes

In Chemical Vapour Deposition (CVD), technicians grow diamond layer by layer from a carbon‑rich plasma inside a vacuum chamber. A thin diamond seed plate anchors growth; the chamber is filled with hydrogen and a carbon‑bearing gas (often methane) and energised by microwaves or a hot filament to about 800–900°C. The plasma splits the gas, carbon deposits onto the seed, and crystallises into diamond. Teams periodically pause growth to remove any graphite. Multiple seeds can grow at once; rough typically emerges as a square plate. Timeframes run days to weeks, commonly a couple of weeks for gem sizes.

1. Prepare seeds: Meticulously clean thin seed plates (around 300 µm, ~10×10 mm).
2. Load and seal: Place seeds in the vacuum chamber and seal against contamination.
3. Add gases: Introduce hydrogen plus a carbon source; avoid nitrogen that can yellow stones.
4. Ignite plasma: Use microwaves or a hot filament; stabilise at ~800–900°C.
5. Grow layers: Carbon radicals deposit atom by atom; pause to remove any graphite and track thickness.
6. Harvest rough: Cool and remove cubic plates; typical growth cycles are days to weeks per batch.

HPHT vs CVD: key differences, pros and cons

When you compare how lab diamonds are made with HPHT versus CVD, the output is the same diamond; the contrasts lie in growth conditions, rough crystal shapes and typical as‑grown features. HPHT crystallises carbon around a seed under extreme pressure and heat; CVD deposits carbon from a carbon‑rich plasma onto a seed. CVD is widely used for jewellery‑grade growth, while many jewellers note HPHT can deliver whiter results with less post‑growth work. Both methods can produce exceptional stones.

• HPHT pros: Mimics mantle conditions; can yield bright, white diamonds without post‑growth; rough often shows cuboctahedral form; gem sizes commonly grown in weeks.
• HPHT considerations: May contain minute metallic traces; requires high‑pressure presses and significant energy; historically prevalent in industrial synthesis as well as gem growth.
• CVD pros: Batch growth of multiple seeds at once; lower temperatures (~800–900°C); often quicker, less costly and uses less energy for producers; fine layer‑by‑layer control.
• CVD considerations: As‑grown stones can appear brown/yellow and often need heat/HPHT treatment; may show internal graining; nitrogen in the gas can yellow stones; rough emerges as square plates.

Post-growth treatments and colour engineering

Even well‑grown crystals sometimes need finishing. Many CVD diamonds emerge brownish or yellowish and are routinely improved by post‑growth heat/HPHT treatment to achieve colourless grades; in some cases, heavy treatment can leave stones looking slightly milky or hazy. HPHT‑grown stones may also receive heat treatments to refine colour and clarity or to create fancy colours. Any treatments and the growth method are disclosed on grading reports from labs such as GIA and IGI.

• HPHT annealing (post‑growth): Lightens CVD browns/yellows; can enhance clarity.
• Heat with trace elements: Boron can produce blue; nickel can produce green.
• Irradiation (with subsequent heating): Used to achieve pinks and reds.
• In‑growth colour engineering: Adding boron or nitrogen during CVD yields blue or yellow hues; excess nitrogen risks yellowing.

Choose stones with transparent disclosure and eye‑clean, lively optics after treatment.

From rough to ring: cutting, polishing and grading

Once HPHT or CVD rough leaves the growth chamber, expert cutters transform it into a bright, durable gemstone. Rough shapes vary—HPHT crystals often show cuboctahedral forms, while CVD rough emerges as square plates—but both are sawn with lasers and finished using traditional polishing to maximise beauty and retain weight.

1. Plan the cut: Select the best shape and orientation to balance carat yield with light performance.
2. Saw and shape: Laser saw the rough; round stones are rounded by bruting.
3. Facet and polish: Create and refine facets to symmetry standards; finish the surface for brilliance.
4. Grade the diamond: Independent labs such as GIA and IGI assess the 4Cs—cut, colour, clarity and carat—and record the growth method and any treatments on the report.

How long does it take to grow a lab diamond?

If you’re wondering how long it takes once the seed is in, think weeks rather than years. Timings vary by method, target size and colour, but most jewellers quote roughly 2–4 weeks for a single gem-quality stone to grow.

With HPHT, very small crystals can form in hours, while jewellery sizes usually take weeks and larger gem roughs often need around a month under sustained heat and pressure. CVD growth runs days to weeks; multiple seeds can be grown in a batch, with periodic pauses to remove any graphite. Adding nitrogen can speed CVD, but risks yellow tints, so it’s avoided for colourless goals. Remember, cutting, polishing and grading add further time to the finished ring.

Quality factors to watch for in lab-grown diamonds

Choosing well in lab‑grown diamonds is much like mined: prioritise beauty you can see. Cut drives sparkle, then colour and clarity. Because of how lab diamonds are made, each method can introduce tell‑tale features, so read the grading report and view the stone under good lighting or video before you decide.

• Cut first: Favour Excellent cut for rounds (or Excellent polish and symmetry for fancy shapes) to maximise brilliance.
• Colour check: D–F looks icy white. Many CVD stones start brown/yellow and are lightened; verify any treatment on the report.
• Clarity sweet spot: VS2–SI1 often looks eye‑clean. Watch for internal graining (common in fast CVD growth).
• HPHT inclusions: Tiny metallic residues can occur; usually not visible but should be noted on clarity plots.
• Treatment transparency: Post‑growth HPHT/heat should be disclosed by GIA/IGI; heavy treatment can leave slight milkiness—inspect carefully.
• Overall appearance: Choose lively, crisp scintillation over paper specs; a well‑cut HPHT or CVD diamond can look identical face‑up.

Certification, testing and how labs identify origin

Lab‑grown diamonds are graded just like mined stones. Independent laboratories such as GIA and IGI assess the 4Cs and clearly disclose origin (lab‑grown) plus growth method (HPHT or CVD) and any post‑growth treatments. Because their chemistry is identical, standard diamond testers read them as diamond; distinguishing lab vs natural requires specialist laboratory equipment. GIA reports for lab‑grown are commonly issued digitally, while IGI frequently provides physical certificates, so keep copies with your insurance paperwork.

• What labs record: Growth method (CVD/HPHT) and any heat/HPHT or irradiation treatments are stated on the report.
• How labs tell origin: Laboratory processes leave tell‑tale features gemmologists can identify under close examination; in rough, HPHT often shows cuboctahedral forms and CVD grows as square plates.
• Bottom line: Certification provides transparent disclosure so you know exactly how your lab diamond was made and finished.

Sustainability and ethics: energy use, renewables and mining impact

Both mined and lab-grown diamonds have impacts, but they’re different. Mining disturbs vast areas of land and can take decades to rehabilitate, while labs trade excavation for electricity. When you understand how lab diamonds are made, it’s clear the major footprint is energy; producers are steadily improving efficiency and increasingly using renewables (some even solar-powered). Legitimate mines follow the Kimberley Process to reduce conflict risk, but lab-grown typically offers tighter origin traceability and controlled working conditions.

• Energy use: Growth requires significant electricity; renewables can cut emissions. CVD is typically quicker and less energy-intensive for producers than HPHT.
• Land impact: Labs need comparatively little space; mining demands large-scale excavation with long-term land recovery.
• Traceability and labour: Lab-grown origin and treatments are disclosed on reports; responsible mining initiatives exist, but oversight varies by operation and region.
• Practical takeaway: Ask about the power source behind growth and the provenance of mined stones; choose disclosed, responsibly produced diamonds either way.

Cost and value: how pricing compares with natural diamonds

Because they’re grown in weeks in compact facilities rather than mined from vast deposits, lab‑grown diamonds are significantly cheaper for the same 4Cs. Multiple sources note savings of around 40–50% versus comparable natural diamonds, largely due to more efficient, scalable production. That price gap lets many buyers step up cut, colour or carat without stretching budget, while still receiving GIA or IGI certification and identical optical and physical properties.

• Typical pricing: Lab‑grown often cost 40–50% less than natural for similar grades.
• Why cheaper: Faster, controlled growth and lower overheads make production more cost‑effective.
• Resale and investment: If investment is your priority, natural diamonds are generally preferred.
• Insurance: You can insure lab‑grown rings; premiums reflect the invoice value and may be lower than for mined stones.

Common questions about lab-grown diamonds

Here are quick answers to the questions we’re asked most about how lab diamonds are made and what that means for your ring.

• Are they real diamonds? Yes — they have identical chemical, physical and optical properties; only the origin differs.
• Do they test as diamond? Yes — standard testers read “diamond”; only specialist lab tools confirm origin.
• How long do they take to grow? Typically 2–4 weeks, varying by method (HPHT/CVD) and target size.
• Can you make one at home? No — it requires high‑pressure presses or CVD reactors and is unsafe.
• Do they come in colours? Yes — yellow, blue, pink, green and more via trace elements or post‑growth treatment (disclosed).
• Are they certified? Yes — GIA/IGI grade the 4Cs and state CVD/HPHT growth and any treatments.

Choosing between lab-grown and natural for your ring

Both options are real diamonds with identical hardness, brilliance and certification standards, so your choice comes down to meaning, budget and ethics. Natural diamonds carry geological rarity and the romance of deep time. Lab-grown diamonds offer the same beauty for less, clearer origin traceability and the chance to prioritise cut, colour or carat within a set budget. Either way, you can create a bespoke ring that reflects your story.

• Budget and size: Lab‑grown typically cost 40–50% less, helping you step up carat or quality.
• Meaning: Natural = rarity and history; lab‑grown = innovation and transparent origin.
• Sustainability: Mining impacts land; labs use significant energy—ask about renewable power.
• Colour goals: Fancy colours and larger sizes are more attainable with lab‑grown.
• Future value: If investment matters, natural is generally preferred; buy primarily for love.
• Timing and availability: Lab‑grown can be grown in weeks and are widely available in popular specs; both are cut, polished and graded before setting.

A thoughtful consultation with a gemmologist will align these trade‑offs with your priorities and budget.

Key takeaways

Lab‑grown diamonds are real diamonds grown from seed by HPHT or CVD, typically in weeks, then cut, polished and graded like mined stones. Reports from GIA/IGI disclose origin, method and any treatments. Your choice comes down to budget, meaning and sustainability preferences.

• Two proven methods: HPHT (high pressure/heat) and CVD (carbon‑rich plasma).
• Seeds matter: Tiny diamond plates guide orderly, high‑quality growth.
• Typical timeframes: Gem sizes usually grow in about 2–4 weeks.
• Finishing & grading: Cut/polish, then GIA/IGI certify method and treatments.
• Price & ethics: Often 40–50% less than mined; energy vs land impacts—ask about renewables.

For personal advice and hand‑selected stones, meet our Hatton Garden team at A Star Diamonds.