CVD (Chemical Vapor Deposition)

CVD — Chemical Vapor Deposition — is the lab-grown diamond synthesis method that builds diamond crystal layer by layer from a hot methane-hydrogen plasma at relatively low pressure (typically 50 to 200 millibar, vs the gigapascal pressures used in natural diamond formation). It is the dominant method for gem-quality lab-grown production today, having largely displaced HPHT for new growth runs above about 0.5 ct.

The process starts with a thin slice of diamond (the seed plate) placed inside a vacuum chamber. The chamber is evacuated and filled with a mix of methane (the carbon source) and hydrogen at controlled pressure. Microwave or hot-filament energy excites the gas into a plasma, breaking the methane molecules into atomic carbon. The carbon atoms deposit onto the seed plate and bond into the diamond lattice structure, growing the crystal layer by layer. A typical CVD growth run takes 2 to 4 weeks to produce a finished crystal that yields a 1 to 5 ct polished stone.

CVD stones are typically Type IIa — the synthesis path produces near-pure carbon crystal with negligible nitrogen incorporation. Some CVD reactors deliberately introduce nitrogen, boron, or silicon as dopants to produce specific colors (yellow, blue, or to suppress brown growth-tint), but the colorless CVD market is overwhelmingly Type IIa. The as-grown product often shows a brown tint from carbon vacancy defects formed during growth; the brown is removed by post-growth HPHT treatment, which anneals the vacancies and shifts the color toward D-F. Most colorless CVD on the market today has received post-growth HPHT — disclosed on the IGI or GIA Laboratory-Grown Diamond Report as "Post-growth treatment: HPHT."

CVD origin is identified by DiamondView fluorescence (orange or red, with visible horizontal growth lines from the seed plate) and FTIR spectroscopy (characteristic CVD-related absorption peaks). The identification is reliable; no current grading lab confuses CVD with natural in routine inspection.

CVD has driven lab-grown diamond pricing collapse. Production scale has grown 20% to 30% per year through the late 2020s; wholesale prices on 1 ct D-IF CVD rounds have fallen from $5,000 per carat in 2020 to under $500 per carat in 2026. Retail markups have not compressed at the same rate, so the gap between wholesale and retail in lab-grown is wider than in natural — buyers shopping wholesale-aware can find 1 ct D-VS1 CVD rounds at under $1,000 per carat all-in.

The grading vocabulary on CVD reports matches natural (D-Z color, FL-I3 clarity) but the underlying market is fundamentally different.