CVD diamond is laboratory-grown diamond produced by chemical vapour deposition, the process in which diamond is grown by depositing carbon atoms from a gas-phase plasma onto a thin diamond seed plate held inside a low-pressure microwave reactor. The technique is one of the two principal commercial methods of laboratory diamond synthesis, alongside HPHT (high-pressure-high-temperature), and since approximately 2014 it has come to dominate the laboratory-grown gem-quality diamond market. The output of the technique is real diamond, chemically and crystallographically identical to natural mined diamond, distinguished only by its mode of formation and by certain growth-related features that laboratories use to identify it.

The chemistry

The CVD process begins with a thin slice of natural or HPHT-grown diamond as a seed substrate. The seed is placed in a low-pressure reactor (typically 25 to 200 millibar) and heated to around 700 to 1,200°C. A gas mixture of methane (CH₄) and hydrogen (H₂) is introduced, with the methane providing the carbon source and the hydrogen serving to selectively etch away non-diamond carbon (graphite and amorphous forms). A microwave plasma activates the gases, breaking the methane into carbon-containing radicals, and the radicals deposit onto the seed surface. With proper conditions the deposition proceeds in the diamond crystal structure rather than in graphite, and the seed grows in thickness over hours, days, or weeks. The growth direction is typically along the {100} face, although other orientations are used for specialised purposes.

Modern gem-quality CVD reactors typically grow rough diamond at a rate of around five to fifteen micrometres per hour, allowing a one-carat finished stone to be produced from rough grown over several weeks. After growth the rough is cut and polished using the same techniques as natural diamond.

Origins and commercialisation

CVD diamond was first synthesised in the 1950s by Soviet and American scientists, but the early product was thin polycrystalline films suitable only for industrial coatings. Single-crystal gem-quality CVD diamond emerged from research at Apollo Diamond, Element Six (a De Beers subsidiary), and several academic groups in the late 1990s and early 2000s. Commercial gem-quality production began around 2003-2008 from firms including Apollo, Gemesis (later Renaissance), and several others, and accelerated rapidly from 2014 onward as Chinese, Indian, and American producers brought capacity online. By the early 2020s, CVD diamond was a substantial fraction of the laboratory-grown gem market, particularly at sizes of one carat and above, and prices for laboratory-grown diamonds had fallen by approximately 80 to 90 percent against natural diamond at comparable grades.

Identification

CVD diamond is reliably identified by laboratory testing, although not by the unaided eye. The most useful diagnostic features include: distinctive growth patterns visible under cross-polarised light, showing strain features along growth layers; characteristic photoluminescence (PL) features, particularly the 596/597 nanometre doublet, the 737 nanometre silicon-vacancy line, and others, that distinguish CVD from natural and HPHT material; UV fluorescence patterns, often weak under long-wave UV but with specific phosphorescence behaviour under deep UV; and FTIR spectroscopy showing the type IIa or low-nitrogen IaA character typical of CVD growth. The Gemological Institute of America's screening instruments (the GIA iD100), De Beers's SYNTHdetect and DiamondView, and HRD Antwerp's instruments are widely used in the trade for screening, with confirmed identification provided by laboratory reports.

Post-growth treatment

Many CVD diamonds undergo post-growth treatment, particularly HPHT annealing in which the as-grown stone (often slightly brown due to growth-related defects) is held at high pressure and high temperature for a short period to anneal out the brown component and produce a near-colourless or fancy-coloured outcome. This is now the dominant production model for high-quality CVD melee and stone goods. Other CVD products are grown directly to fancy colours (yellow through blue) by introducing nitrogen, boron, or other dopants during growth.

Disclosure

CIBJO, the FTC, and the major trade associations require disclosure of laboratory-grown origin at every stage of sale. The current preferred terminology is "laboratory-grown" rather than "synthetic" or "man-made", on the reasoning that the product is genuine diamond and the method of formation is the only meaningful distinction. Laboratory reports for CVD diamonds explicitly note the CVD origin, and many include the manufacturer where it can be determined from growth-feature analysis. The major laboratories - GIA, IGI, HRD, GCAL - all issue grading reports for laboratory-grown diamonds with the CVD or HPHT identification disclosed.

Market position

CVD diamond now occupies a substantial and rapidly growing position in the diamond market, particularly in the engagement-ring segment of the United States and increasingly in Europe and Asia. The price differential between CVD and natural diamond has stabilised at approximately one-tenth to one-twentieth of natural diamond at comparable grades, and the segment is treated by the trade as a distinct product category rather than as a simulant or competitor. The De Beers Group, after several years of public resistance, launched its own laboratory-grown brand Lightbox in 2018 with a flat-rate pricing model designed to position laboratory-grown diamonds firmly outside the natural-diamond engagement-ring market; the strategy has produced mixed results as the broader laboratory-grown market has continued to expand.