The HPHT Method
The HPHT growth method is the original method of creating lab-grown diamonds. Gem quality HPHT diamonds were introduced in the 1950s. Outside of growing diamonds, post-HPHT treatment can also be used to enhance the color of diamonds (whether natural or lab-grown) to make them colorless, pink, green, blue, or yellow.
To grow an HPHT diamond, a small diamond seed is placed in carbon, the element that diamonds are made of. The diamond seed is exposed to extreme heat and pressure, replicating the way diamonds are naturally grown underground by the earth. The diamond seed is exposed to temperatures of over 2,000 degrees Fahrenheit and pressure of about 1.5 million PSI (pounds per square inch). The carbon melts and forms a diamond around the seed. It is then cooled and the diamond is formed.