One of two processes is usually used to produce lab-grown diamonds: the CVD process (‘chemical vapour deposition’) or the HPHT process (‘high pressure high temperature’). Both processes are fundamentally different. Small, thin pieces of diamond known as ‘seeds’ are used as starting material for the CVD process. Larger stones can grow in the vacuum chamber under specific process conditions. Lab-grown diamonds from Nevermined are grown exclusively using the CVD process.
The CVD process for lab-grown diamonds
Chemical vapour deposition is the more recent development of the two aforementioned processes in diamond production. In the CVD process, diamond seeds are placed in a chamber first of all. The seeds themselves are made of diamond which is also grown in the laboratory. The chamber, which is in a vacuum, is flooded with hydrogen. With the help of microwaves, energy is added to the hydrogen gas, igniting a plasma. In simplified terms, a plasma is a mixture of particles that can be thought of as a fourth state of matter (in addition to solid, liquid and gas). Further gases such as methane and other additives are subsequently added to the plasma. In this process, the plasma heats the seed to a temperature of up to 1,000 °C. The high temperatures that arise in the chamber cause the chemical compounds of the added gases to break down. This releases carbon – the material diamonds are made of. The carbon particles now settle on the surface of the seeds and allow the diamond to grow, atom by atom, layer by layer. Diamond manufacturers are walking a physical tightrope here, as they have to carefully balance temperature, pressure and gas composition in their vacuum chamber. Fluctuations could affect the growth of the diamond, its clarity or its colour. If the complicated undertaking is successful, cuboid rough diamonds are created within a very short time. They are then processed and polished like natural specimens.
The HPHT process for lab-grown diamonds
When using the high-pressure, high-temperature process, a hydraulic press is used to mimic the conditions under which natural diamonds are formed inside the earth. Here, too, diamond seeds are initially inserted into a specially developed machine that is capable of generating extremely high pressure. Its chamber is heated to temperatures of up to 3,500 °C under up to 60,000 times the atmospheric pressure. Inside the capsule, a high-purity carbon starting material (such as graphite) dissolves in a flux of molten metals. This lowers the temperature and pressure and releases carbon atoms from the starting material. The carbon atoms migrate through the flux towards the cooler diamond seed. They precipitate upon it – and the laboratory diamond begins to grow. Within a few weeks, diamonds are created in this way. Adding a catalyst can accelerate the process and also means less pressure (‘only’ around 100,000 times atmospheric pressure) and lower temperatures (up to 2,000°C) are required. The largest diamond produced in the laboratory to date using the HPHT process was grown at the end of 2021 and weighs around 150 carats.