Chemical Vapour Deposition (CVD) is a more recent diamond growing technique during which a gemstone is grown from a hydrocarbon gas mixture.
During the CVD process, a thin wafer of a diamond crystal is placed in a sealed chamber and heated to 800°C. Then the chamber is filled with a carbon-rich gas, such as methane, and get ionized into plasma using lasers, microwaves or others. The ionization breaks the molecular bonds in the gas, and pure carbon gets deposited on the wafer of a diamond crystal (usually HPHT synthetic), growing a gemstone atom by atom, layer by layer.
The CVD diamond growing process has a couple of advantages over the HPHT process. High pressure is not needed, and temperature, while high, do not need to be above 1400°C, meaning this process is much less costly. Finally, the CVD method can produce colourless gems.