From Carbon to Carat: The 7 Stages of Lab Grown Diamond Manufacturing

A lab grown diamond starts as a sliver of carbon smaller than a grain of rice and, roughly two to three months later, exits a gemological lab as a graded, certified stone that is physically and chemically identical to one pulled from the earth. The process runs through seven distinct stages, and knowing each one helps you read a grading report, compare stones with confidence, and understand exactly what you are paying for.

Every stage below requires specialized equipment, trained technicians, and decisions that directly affect the final stone’s cut, color, clarity, and carat weight. Skip one step or rush it, and the result shows up on the certificate.

What happens before growth even begins?

The first stage is seed selection. A seed is a thin slice of an existing, high-quality diamond crystal, typically less than 1 millimeter thick. It acts as the template that new carbon atoms bond onto during growth. Seed quality matters because any structural irregularity in the starting slice tends to propagate outward as the crystal grows, which is why manufacturers are selective about which seeds they use.

Seeds destined for CVD (Chemical Vapor Deposition) growth are usually cut from {100} crystallographic planes, while HPHT (High Pressure High Temperature) growth may use seeds oriented differently depending on the press geometry. At this point, the manufacturer also decides which method to use, and that choice shapes everything downstream.

How do the two growth methods actually differ?

Stage 2: HPHT Growth. The seed is placed inside a press cell layered with a carbon source (typically graphite) and a metal catalyst such as iron, nickel, or cobalt. The cell is compressed to roughly 870,000 pounds per square inch and heated to between 1,300 and 1,600 degrees Celsius. At those conditions, the catalyst dissolves the carbon source and carbon atoms precipitate onto the seed, building the crystal layer by layer over several days to a few weeks.

Stage 3: CVD Growth. The seed is placed inside a vacuum chamber. A carbon-rich gas, most commonly a methane and hydrogen mixture, is pumped in and ionized into a plasma using microwave energy. Carbon atoms break free from the gas and deposit onto the seed one atomic layer at a time. CVD typically runs for two to four weeks to produce a 1-carat rough, and the process tends to yield very high-clarity stones. The tradeoff is that CVD growth often produces a brownish undertone caused by nitrogen-vacancy defects, which leads directly to the next stage.

Is post-growth treatment standard practice?

For CVD diamonds, yes, in most cases. Many CVD-grown stones go through an HPHT annealing step after growth: the already-formed rough is placed back into a high-pressure, high-temperature environment, which reorganizes defects at the atomic level and permanently improves color. Nothing is added to the diamond during this process; the crystal lattice is corrected, not coated. A full IGI grading report will note whether post-growth treatment was applied, so buyers can verify exactly what they are purchasing.

HPHT-grown diamonds occasionally show a faint yellowish tint from trace metallic inclusions left by the catalyst, though modern press designs have reduced this considerably. Neither growth method is categorically superior; the quality of the final stone depends more on the precision of the specific lab’s process than on which method was chosen.

How is rough diamond crystal turned into a gem shape?

Stages four and five cover the physical transformation from rough crystal to polished stone.

Stage 4: Planning and Sawing. Once the rough crystal leaves the growth chamber, it goes to a cutting facility where planners study it under magnification and often run it through 3D modeling software to map inclusions and determine the highest-yield cut. This decision alone can significantly affect the final carat weight and value. A single rough stone may yield one larger gem or several smaller ones, depending on the internal structure. Once the plan is set, the rough is divided using a laser saw, which burns through the crystal along the chosen line and reduces the risk of fracture that older metal-blade sawing carries.

Stage 5: Bruting, Faceting, and Polishing. Bruting shapes the stone into a rounded outline that forms the girdle. After that, facets are cut and polished onto the stone using diamond-tipped tools. For a standard round brilliant, this means placing 57 or 58 precisely angled facets. Cutters lose roughly 50 to 60 percent of the rough’s original weight during this stage, which is why the planning step matters so much. Faceting and polishing can take anywhere from several hours to several days per stone, depending on the shape and the cutter’s target grades for symmetry and polish.

What does IGI certification actually test?

Stage 6: Quality Control and Certification. The finished, polished stone is sent to an independent gemological lab, most commonly the International Gemological Institute (IGI) for lab-grown diamonds. IGI gemologists grade the stone on the four Cs: carat weight, cut, color, and clarity. Color is assessed in a standardized viewing environment with the diamond placed face-down to eliminate bias, and multiple graders submit independent opinions before a consensus grade is assigned. Clarity is evaluated under 10x magnification, with the scale running from Flawless down to Included.

For round brilliants, IGI compares the stone’s proportions against its own research on brightness, fire, and scintillation to assign a cut grade. Fancy shapes receive separate polish and symmetry grades. The report also identifies the growth method (CVD or HPHT) and notes any post-growth treatment. Every IGI-certified lab-grown diamond receives a laser inscription on the girdle matching its report number, an inscription invisible to the naked eye but readable under magnification that permanently links the physical stone to its certificate.

Stage 7: Setting or Sale as a Loose Stone. After certification, the stone is either set into jewelry or sold as a loose diamond. The IGI certificate travels with the stone either way, so the grading information is available before purchase, not just included in the box afterward.

The Growth Method Is Not the Quality Guarantee

The single factor that most buyers misread is this: the manufacturing method (CVD vs. HPHT) does not determine quality. What determines quality is the precision applied at every stage, from seed selection through the cutter’s decisions during faceting. A well-executed CVD stone will outperform a carelessly grown HPHT stone, and vice versa. The IGI certificate is the only document that tells you what actually came out of that process: the specific grades, the growth method, any post-growth treatment, and the exact measurements of your stone.

When comparing lab-grown diamonds, use the IGI report as your primary tool. The story of how a diamond was made matters, but the grades on that report are what you will see every time you look at the stone. Ouros Jewels carries IGI-certified lab-grown diamonds across a range of sizes, and each listing includes the certificate details so you can compare grades before making a decision.

Frequently Asked Questions

How long does it take to manufacture a lab grown diamond from start to finish?

Crystal growth alone takes two to four weeks for CVD and a similar range for HPHT, depending on target size and quality. Adding post-growth treatment, cutting, polishing, and IGI certification, the full process from seed to certified stone typically runs two to three months in total.

Can you tell the difference between a CVD and an HPHT lab grown diamond just by looking?

No. Without highly specialized gemological equipment, it is impossible to distinguish the two methods visually. The IGI grading report will state the growth method used, so that information is always available to the buyer on paper, even if it is undetectable in person.

Does post-growth HPHT treatment lower the quality or value of a CVD diamond?

No. HPHT annealing corrects color-causing defects at the atomic level without adding any material to the stone. The result is a higher color grade, which increases value. IGI discloses the treatment on the grading report, so there is no hidden information.

Why do lab grown diamonds lose 50 to 60 percent of their rough weight during cutting?

The loss comes from shaping the rough crystal into precise facet angles. A round brilliant requires 57 or 58 facets positioned at exact proportions to maximize light return. Achieving those proportions means removing material that does not serve the optical goal, which is why planning the cut carefully before sawing is so important to final yield.

What does the laser inscription on an IGI-certified lab grown diamond actually say?

The inscription is the IGI report number, etched onto the girdle of the stone. It is invisible to the naked eye but readable under 10x magnification. The number links the physical diamond to its certificate permanently, allowing any buyer or jeweler to verify the stone’s grades and origin at any point in the future.