How Are Lab-Grown Diamonds Made? From Seed to Finished Gem
Updated: Oct 10
A lab-grown diamond starts with a small piece of diamond that already exists. The producer supplies additional carbon and controls the growth environment so that new carbon atoms join the seed's crystal structure, creating a larger rough diamond. That rough then undergoes inspection, planning, cutting, polishing and laboratory assessment before it becomes a finished gem suitable for jewellery.
The process does not turn glass or another imitation material into diamond, and a machine does not produce a sparkling finished gem at the touch of a button. Each stage has its own challenges: whether the seed is suitable, whether growth remains stable, whether the rough contains defects, and how much weight and brilliance can be retained during cutting. This guide follows the manufacturing process step by step. For the material's relationship with natural diamond, see Are Lab-Grown Diamonds Real Diamonds?.
Contents
Figure 1 | An illustration of the manufacturing process from diamond seed to finished gem.
1 Diamond seeds and production preparation
The seed is itself diamond
A diamond seed is a small piece of single-crystal diamond. It provides the starting arrangement of atoms, allowing newly supplied carbon to extend the existing crystal lattice. The seed acts as a structural template; the carbon needed to enlarge the crystal is supplied separately, through a solid source such as graphite or through a carbon-containing gas.
Seeds can come from natural diamonds or from diamonds previously grown by HPHT or CVD. Commercial CVD production commonly uses plates prepared from lab-grown diamond, so it does not require a new natural diamond for every growth run. Suitable material is sliced along a selected crystal orientation, ground and polished to prepare the growth surface. Some producers make their own seeds, while others purchase them from specialist suppliers.
There is therefore no endless loop in the question of where the first seed came from. Existing natural diamond can provide a starting point, and successfully grown lab diamonds can supply material for subsequent seeds. Seeds are normally prepared by material suppliers or growth laboratories, rather than by a jewellery retailer during setting.
Figure 2 | An illustration of diamond seed plate preparation. The thin seed plates and the larger rough diamond are separate specimens.
What must be prepared before growth?
The seed's orientation, dimensions and defects must first be checked. In a typical CVD process, the producer selects a suitable crystal face, prepares a flat surface and removes damage or contamination left by slicing and polishing. A surface that appears smooth may still contain tiny scratches or subsurface defects, which can extend into the newly grown material.
Inspection may involve microscopes, observations under polarised light, surface measurements, and spectroscopic or crystal analysis appropriate to the quality requirements. More demanding surface preparation can also use plasma etching to remove a thin layer damaged by mechanical processing. Equipment varies between factories, but suitable seeds, clean surfaces and consistent preparation are fundamental to stable growth.
Equipment and environmental control
CVD production needs a low-pressure reaction chamber, vacuum equipment, high-purity gas supplies, gas-flow controls, an energy source, and systems for mounting the seeds and managing temperature. Microwave plasma equipment is common in gem-quality single-crystal production. Operators control chamber pressure, gas proportions, plasma conditions and seed temperature, while managing cooling, chamber cleanliness and sealing.
HPHT production uses a high-pressure press and a heating system. The carbon source, metal solvent and seed are placed inside a growth assembly. The equipment must withstand very high pressure and temperature while establishing a temperature difference that supports carbon transport and crystallisation. An ordinary oven cannot perform this process.
Lab-grown diamonds are produced in countries including China, India and the United States. Growth factories, seed suppliers and cutting workshops may be located in different regions, with rough diamonds transported to specialist processing centres. A diamond's growth location and cutting location are therefore not necessarily the same.
What makes the process technically demanding?
Equipment is only one part of the investment. Consistently producing gem-quality rough requires knowledge of crystal growth, material purity, thermal fields or plasma control, equipment maintenance and defect analysis. When colour or clarity misses the target, the team must trace the cause to the seed, feedstock, chamber contamination or growth settings.
Growing diamond at all and consistently growing diamond of a target size, colour and clarity are different technical achievements. The latter requires repeated process validation and control of variation between batches. Buying a machine or following a fixed recipe alone does not provide that capability.
2 The two main growth methods
Both main methods begin with a seed, but carbon reaches the seed in different ways. In high pressure, high temperature growth, or HPHT, carbon first dissolves in molten metal and then crystallises as diamond at the cooler seed. In chemical vapour deposition, or CVD, a carbon-containing gas and hydrogen are energised in a low-pressure chamber. A series of reactions deposits diamond material onto the seed, layer by layer.
Figure 3 | An illustration of carbon supply and crystallisation in CVD and HPHT. The drawing is not to scale.
Both methods can produce lab-grown diamonds suitable for jewellery. The method's name is not a quality grade. For a detailed explanation of the equipment, rough characteristics and post-growth treatment, see CVD vs. HPHT Lab-Grown Diamonds. Here, we continue with the time and quality constraints encountered as the rough grows.
3 Growth time and quality risks
How long does growth take?
Growth time depends on the method, rough size, equipment and quality target. Small HPHT crystals can grow relatively quickly, while larger gem-quality crystals require longer runs. GIA's technical review describes a range from about an hour to several weeks. That range covers different crystal sizes and requirements; it does not mean that any jewellery diamond can be grown in one hour.
Gem-quality CVD rough commonly takes several weeks to grow. GIA's educational material has used approximately four to six weeks as a typical illustration, but individual batches can be faster or slower. Exceptional large, high-quality crystals may take longer. Additional time is needed for seed preparation, equipment cleaning, any necessary interruptions during growth, post-growth treatment, cutting, polishing and laboratory assessment.
Rough weight is also different from finished carat weight. GIA's 2024 review cites a public example of a CVD rough weighing about 17 carats, grown in approximately 40 to 45 days and ultimately cut into a 7.50-carat diamond graded F colour and VVS2 clarity. This is a specific case, not a universal formula for how many days are needed per carat. It illustrates the difference between rough weight, usable volume and the final gem.
What makes growth faster or slower?
In CVD, gas composition, flow, energy input, pressure, seed temperature and mounting all affect growth rate and material quality. Some processes use small amounts of additives to increase growth speed, but faster deposition can involve trade-offs in colour, defects or surface quality. Producers must balance output against the quality of usable rough.
HPHT requires control of the carbon source, metal solvent, pressure and temperature gradient so that carbon reaches the seed at a suitable rate. A mismatch between carbon supply and crystallisation can affect crystal shape or trap metal solvent inside the diamond. The goal is a rate that consistently produces the required quality.
Larger dimensions add difficulty. CVD chiefly builds thickness on the seed surface, so seed area and usable thickness influence the shapes that can later be cut. HPHT has its own limits in growth space, thermal conditions and carbon transport. If a run must be interrupted to remove non-diamond carbon, inspect the surface or resume growth, the overall production time increases.
Are high-colour and fancy-colour diamonds harder to make?
A colourless or high-colour-grade target demands tighter control of impurities and colour-causing lattice defects. Nitrogen can give some HPHT diamonds a yellow colour, while boron can produce blue. A brown tint in some as-grown CVD diamonds may be associated with vacancy-related defects. Simply allowing the same crystal to grow for a few more days does not automatically create a higher colour grade.
Some rough grows colourless directly, while other material receives post-growth treatment, such as HPHT treatment, to improve colour. HPHT growth and HPHT post-growth treatment are separate stages: a CVD-grown diamond subsequently treated by HPHT is still CVD-grown. A lower colour grade does not necessarily indicate simpler production, because colour depends on feedstock, growth conditions, defects and treatment.
Fancy-colour lab-grown diamonds require deliberate control of the conditions responsible for colour. Yellow can be associated with nitrogen and blue with boron; some pink, red or green products receive irradiation and annealing after growth. Achieving a particular hue, strength and evenness of colour requires the appropriate process. Fancy colours cannot all be described as easier or harder to make, and colour alone cannot determine the number of growth days.
Can a diamond grow indefinitely if we keep waiting?
No. Usable size is limited by the seed, chamber space, carbon supply and the stability of the growth region. As a crystal becomes thicker or larger, temperature distribution, surface conditions and stress can change. The process must remain suitable as growth progresses. More time cannot replace equipment capacity or crystal quality control.
In CVD, unwanted crystals or non-diamond carbon forming in unsuitable locations can interfere with continued single-crystal growth. Existing seed defects may also propagate into the new material. Thermal stress or pre-existing fissures can increase the risk of cracking. Producers stop according to the target dimensions and inspection results rather than extending growth indefinitely to maximise weight.
Can growth fail?
Yes. Failure does not always mean that the entire crystal breaks apart. Rough may grow successfully but miss the target in colour, clarity, dimensions or usable cutting volume. The following are examples of problems that need to be controlled. Whether material can be recovered depends on the location and severity of the defects and the results of further inspection.
Figure 4 | An illustration of growth quality problems: a fissure at upper left, a brown tint outside a colourless target at upper right, dark inclusions at lower left, and irregular growth with non-diamond carbon at lower right. Actual defects require inspection.
Problem | Possible result | What needs control or inspection |
Poor seed or surface quality | Defects propagate, surfaces become rough, or unwanted crystals form | Crystal orientation, seed selection, surface damage and cleanliness |
Impurities or colour-causing defects exceed the target | Yellow, brown or blue tints, or uneven colour distribution | Feedstock purity, growth recipe and assessment of post-growth treatment |
Non-diamond carbon or unsuitable growth conditions | Growth is disrupted and usable single-crystal volume is reduced | Plasma conditions, growth surface, cleaning and any resumed growth |
Trapped metal or other inclusions | Lower clarity and defects that must be avoided during cutting | HPHT crystallisation conditions and internal rough inspection |
Stress, fissures or changing equipment conditions | Local cracking, interrupted growth or missed target specifications | Thermal conditions, existing defects, equipment stability and when to stop |
These problems also explain the technical bottleneck. Equipment supplies the conditions for growth, but the team must identify the causes of defects, improve subsequent batches and judge which rough is worth processing further. There is no single success rate that applies to every producer, size and quality target.
4 Cutting and polishing
What does newly grown rough look like?
A newly grown diamond usually lacks the sparkling facets of a finished jewellery gem. Common CVD rough is tabular or block-like. Its outer edges may contain non-diamond carbon that must be removed, and some specimens have a brown tint. HPHT rough commonly has several natural growth faces, a different shape from a CVD plate, and may contain metal solvent inclusions or other growth residues. The precise appearance depends on the seed and growth conditions.
Figure 5 | An illustration of as-grown lab diamond rough: a tabular CVD specimen on the left and a multi-faced HPHT crystal on the right. Neither has been cut or polished; shape and colour can vary with growth conditions.
After removing the rough, the producer cleans and inspects it, identifying the seed position, surface condition, fissures and inclusions. This helps determine whether treatment is needed, which areas are usable and which finished gems can be cut. The weight at removal is a starting point, not the eventual weight of jewellery-ready diamond.
Is the cutting process the same as for natural diamonds?
The main principles are the same. Both materials are diamond, so cutting and polishing must account for crystal orientation, cleavage, internal defects, facet angles and surface finish. Being lab-grown does not make diamond a material that can be sliced with an ordinary blade.
The main differences concern the starting rough. Lab-grown material has a seed position, growth habit and characteristic defects to consider. The tabular volume of CVD rough particularly affects the depth and shapes available for cutting. Planners incorporate those factors into their decisions, just as each natural rough must be assessed for its individual shape and defect distribution.
Step 1 Inspect the rough and build a 3D model
Modern cutting factories commonly weigh, measure and inspect the rough before using 3D scanning and planning software as appropriate. An external scan records its three-dimensional outline; inclusion scanning or microscopic inspection helps locate internal defects. Scanning the outer shape alone is not the same as seeing every internal feature. The two types of information serve different purposes.
Not every small rough diamond passes through the same advanced scanning system. Factories choose their workflow according to size, value and processing requirements. For rough that needs precise use of volume and careful avoidance of defects, however, computer models are important planning tools.
Figure 6 | An illustration of 3D rough planning and enclosed laser-cutting equipment.
Step 2 Compare cutting plans
Planning software places possible finished shapes inside the rough model and compares options, such as one large gem or several smaller ones. The plan considers inclusions, fissures, usable depth, expected clarity, facet proportions and material lost during cutting. Our guide to different diamond shapes explains common finished outlines.
Planners do more than maximise the number of carats retained. Keeping extra weight may require less favourable proportions or more visible inclusions, while removing more material may improve appearance or clarity. Finished size and quality must therefore be assessed together. Scanning, software calculations and professional judgement determine where the cuts are made.
Step 3 Laser division and shaping
Once a plan is approved, the factory secures the rough, aligns it and uses laser equipment to divide and shape it. Depending on the material, this may include removing the seed, cutting away unsuitable outer layers or defective areas, and separating the rough into planned blanks. Laser cutting removes a finite width of material, so the plan must allow for the cutting kerf and subsequent finishing.
Laser cutting does not complete every facet at once. It first divides and shapes the material; girdle preparation, main facets and fine polishing follow. Operators also control cutting settings and inspect for damage. Stress or fissures in the rough create risks that a computer model alone cannot eliminate.
Round diamond girdles may be formed by bruting equipment or laser processing, while fancy shapes are prepared to their intended outlines. Modern machinery can automate many operations, but people still assess the rough, choose the processing approach and manage exceptions.
Step 4 Form the facets and polish each surface
The cutter first establishes the main facets and then completes the remaining facets and final polish. A specialised holder secures the diamond, controlling its angle and position as each facet contacts the polishing surface. Traditional diamond polishing uses a horizontal rotating metal wheel called a scaife, together with diamond abrasive.
Diamond can be polished with diamond abrasive because of the interaction between the abrasive and the workpiece, combined with differences in wear along different crystal directions. The polisher must find a workable direction and control angle, pressure and time to produce a flat, polished surface. Excess force does not automatically improve the finish. Poor processing can leave polishing marks, surface damage or unsatisfactory facets.
Figure 7 | An illustration of a diamond secured in a holder and polished facet by facet on a horizontal wheel.
Cutting and polishing also require control of symmetry and proportions. Facet angles, girdle thickness, table size and depth affect how light travels through the gem. Factories use magnification and proportion-measuring equipment to check progress and make corrections where needed. For the finished result, see our guide to hearts and arrows and diamond cut quality.
Is polishing done by hand or by machine?
Both approaches are used. A factory may employ traditional manual holders and polishing equipment, or computer-assisted, semi-automatic and robotic systems. Automation can repeat programmed movements, but rough assessment, planning trade-offs, crystal-direction judgement, equipment calibration and quality checks still require specialist knowledge.
Diamond cutting and polishing is a skilled occupation. A person cannot simply pick up a diamond and finish it without training. Equipment operation can be learned, but handling different shapes, inclusions and processing problems requires experience. Cutting planning, laser operation and facet polishing may also be assigned to different specialists.
Where are diamonds cut, and how is the gem finished?
Surat, in the Indian state of Gujarat, is an important diamond cutting and polishing centre and also has a lab-grown diamond production and processing industry. Such centres benefit from experienced workers, specialist training, equipment services and established supply chains. Diamonds do not have to be cut in one particular country. China and other regions also have diamond-processing capabilities, and producers allocate work according to their capacity and production arrangements.
At the end of processing, the factory cleans the gem and checks its surfaces, facet symmetry, proportions, dimensions and weight, identifying anything that needs reworking. Only after these steps does an irregular or tabular rough become a fully faceted loose diamond. It still needs appropriate identification and quality assessment before stone matching and setting.
5 Laboratory assessment and reports
After cutting and polishing, a producer or supplier can submit loose diamonds to an independent gem laboratory. IGI and GIA provide services for lab-grown diamonds, while NGTC in China also offers synthetic diamond identification and quality assessment. Not every diamond necessarily comes with the same individual report. In particular, a screening document for a parcel of melee diamonds is not equivalent to a full grading report for each stone.
The laboratory first identifies the material and establishes whether it is natural or lab-grown, then assesses quality according to the service requested. Testing can involve microscopy, growth features, ultraviolet responses and spectroscopy. A report records findings for the submitted specimen. It is different from the producer's own label and is not a jewellery valuation.
Laboratory | What to check in a lab-grown diamond report |
IGI | Reports provide 4Cs information, including weight, colour, clarity and applicable cut or finish assessments. Growth-method and treatment comments may be included, depending on the report type and findings. |
GIA | Since 1 October 2025, GIA's Quality Assessment for colourless to near-colourless loose lab-grown diamonds uses the overall descriptions Premium or Standard. Coloured lab-grown diamonds have a separate service; older reports must be understood according to their issue date. |
NGTC | Provides synthetic diamond identification and quality assessment. Distinguish identification-only services from quality assessment, and read the items, terminology and standards stated in the actual report. |
Reports from different laboratories, dates and services should therefore not all be treated as identical 4Cs certificates. For GIA's current system, see GIA Premium and Standard lab-grown diamonds. For the background to the other laboratories, see lab-grown diamond reports from GIA, IGI and NGTC. Always read the actual report for the diamond and the laboratory's applicable service information.
After receiving the report, check the report number, dimensions, weight and, where applicable, the laser inscription on the girdle to confirm that the document matches the stone. If CVD, HPHT or post-growth treatment is listed, distinguish how the diamond grew from how it was treated afterwards.
From seed to finished gem, lab-grown diamond production depends on both growth control and skilled cutting. Understanding the manufacturing process helps separate the requirements for size, colour, clarity and cut, so the finished stone and its report can be assessed together.
