Every laboratory-grown diamond begins with a diamond seed: a thin slice of diamond on which new carbon atoms can build. From there, one of two methods is used to grow a rough crystal, which is then cut, polished and graded like any diamond.
A short history
Scientists tried for more than a century to make diamond. The first reproducible synthesis was achieved by researchers at General Electric in the United States in 1954, using high pressure and high temperature. Those first crystals were tiny and industrial; crystals of gem quality followed in the early 1970s, and chemical vapour deposition was developed in the decades after.
Method 1: HPHT
High pressure, high temperature growth recreates conditions similar to those deep in the earth. Inside a large press, a carbon source is dissolved in molten metal and crystallises onto the seed.
- Pressures of roughly 5 to 6 gigapascals, and temperatures of roughly 1,300 to 1,600 °C.
- Crystals often grow in a cuboctahedral shape.
- Tiny metallic inclusions from the metal solvent can be present.
Method 2: CVD
Chemical vapour deposition works at low pressure. A gas mixture, typically methane and hydrogen, is energised into a plasma inside a vacuum chamber. Carbon atoms separate from the gas and settle on diamond seed plates, building the crystal layer by layer.
- Pressures below atmospheric pressure, and temperatures of several hundred to over a thousand degrees Celsius.
- Crystals grow in flat, tabular shapes.
- Many CVD diamonds are treated after growth, often with heat and pressure, to improve their colour.
Compare the two in CVD vs HPHT diamonds.
After growth
- Treatment, if any, to improve colour.
- Planning and cutting: the rough crystal is studied and cut to the shape that gives the best result.
- Polishing of each facet.
- Grading by a laboratory, which assesses the 4Cs and confirms laboratory origin; many stones are laser-inscribed on the girdle.
What this means for you
The method matters less than the result. Judge a laboratory-grown diamond as you would any diamond: by its cut, colour, clarity, carat weight and the report that describes it.
Seeds and growth
A seed is a thin plate or small crystal of diamond, natural or laboratory-grown, that gives new carbon atoms a pattern to follow. In CVD growth, many seed plates can be placed in the same chamber, so several crystals grow at once. In HPHT growth, one or more seeds sit in a capsule inside the press. Growth continues for days or weeks, and the process is carefully controlled: interruptions or impurities show up later as inclusions or colour.
Where colour comes from
Traces of other elements affect a diamond's colour, in the laboratory as in nature. Nitrogen tends to produce yellow tones; boron produces blue. Growers limit or add these elements depending on the colour they want. Colourless growth requires keeping nitrogen very low, which is one reason many CVD crystals are treated after growth to remove a brownish tint.
Energy
Both methods use a great deal of energy: HPHT to generate pressure and heat, CVD to sustain a plasma for long periods. The environmental footprint of a laboratory-grown diamond therefore depends heavily on where and how that energy is produced. General claims about sustainability should be supported by specific information.
From rough to finished
A grown crystal is rough diamond, exactly like a mined crystal. It is planned with the help of scanning technology, sawn or laser-cut, bruted if it is to be round, and polished facet by facet. The finished stone is then graded, and many are laser-inscribed with a report number and a note of laboratory origin.
Sources: Gemological Institute of America (gia.edu), resources on laboratory-grown diamonds; General Electric Research Laboratory, first reproducible diamond synthesis (announced 1955).
Frequently asked questions
How long does it take to grow a diamond?
Growth typically takes days to weeks, depending on the method and the size of the crystal. Cutting and grading follow.
Are lab-grown diamonds cut differently?
No. Once grown, the rough crystal is cut and polished in the same way as a natural diamond.
Can every shape be made from lab-grown diamond?
Yes. Once grown, the rough crystal is cut into any shape, just like a natural diamond.
Are lab-grown diamonds treated?
Some are, particularly CVD diamonds, which are often treated after growth to improve their colour. Reports usually indicate this.
