There are three techniques to grow HPHT diamonds: the belt press, the cubic press and the split-sphere press. The goal of each is to create an environment of high pressure and high temperature where diamond growth can occur (pressure over 1.5 million pounds per square inch and temperature above 1400°C). Each process starts with a seed of a diamond material placed in carbon and put under extremely high pressure and temperature. In these conditions, carbon melts and forms into a diamond around the seed.