It all starts with a seed. Made from a tiny lab-grown diamond, the seed follows one of two processes: CVD or HPHT. Chemical Vapor Deposition, or CVD, takes the seed and puts it into a plasma reactor chamber where a mix of carbon-rich gasses are added at very low pressure. Microwaves are then introduced to heat the gasses and generate plasma. As the temperature climbs over several thousand degrees, the gas molecules break apart, making way for carbon atoms to bond to the seed one layer at a time.
The High Pressure High Temperature (HPHT) method mimics the conditions of natural diamond creation by placing seeds in a large mechanical press and applying extreme pressure and high temperature to the carbon that is present. The seed acts as a guide for the lattice of carbon (that will soon become the diamond) to grow layer by layer within a matter of days until the desired carat weight is achieved.