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Lab‑grown coloured diamonds,
explained.
How the colours are made, how the stones are graded, and how they compare with natural fancy‑coloured diamonds. Jewellers are welcome to share this guide with their clients.
A real diamond, with its own colour
Lab‑grown diamonds are produced by one of two methods: CVD (chemical vapour deposition) or HPHT (high pressure, high temperature). Colour can come from elements present in the crystal during growth, or be obtained through a controlled treatment after growth, notably irradiation and annealing. These processes modify the structure of the crystal and create the colour centres responsible for the visible hue.
- YellowNitrogen incorporated during growth
- OrangeUsually linked to nitrogen, sometimes combined with post‑growth treatment
- PinkUsually obtained by post‑growth treatment creating colour centres in the crystal structure
- RedProduced by mechanisms similar to pink, with a more pronounced colour intensity
- BlueBoron incorporated during growth
- GreenUsually obtained by post‑growth irradiation, creating specific defects in the crystal structure
Graded like natural fancy colours
Coloured diamonds are graded on hue, tone and saturation rather than on the D‑to‑Z scale. An independent laboratory, IGI for our lab‑grown stones, assigns an intensity grade, from Fancy Light to Fancy Vivid, Deep or Dark. The more saturated the colour, the higher the value.
The certificate states that the stone is laboratory‑grown and discloses any post‑growth treatment. The certificate number is usually laser‑inscribed on the girdle, so stone and certificate can always be matched.
Same diamond, different story
| Natural fancy colour | Lab‑grown colour | |
|---|---|---|
| Material | Crystallised carbon: diamond | Crystallised carbon: diamond, with identical hardness, brilliance and durability |
| Rarity | Only about one natural diamond in 10,000 shows a fancy colour; vivid pinks, blues and reds are among the rarest gems on earth | Grown to order, so saturated colours are consistently available |
| Colour | Each stone is unique; matching pairs and suites are very hard to assemble | Even, vivid colour; matching pairs and calibrated sizes are much easier to source |
| Price | Top natural fancy colours command exceptional prices | A fraction of the price of a comparable natural stone |
| Telling them apart | Only a gemmological laboratory can confirm origin | Always sold with a certificate stating laboratory‑grown origin |