HIGH PRESSURE HIGH TEMPERATURE (HPHT) METHOD
The first basic process to grow diamonds in a laboratory is called High Pressure High Temperature, also known as the HPHT process.
Regardless of which machine configuration is used, be it one large piston or six pistons pressing together, a pressure of at least 700,000 pounds per square inch must be achieved and held. Through modern hydraulics this is relatively easy to do but the challenge is that it must also be heated to over 1200 Celsius in the growth chamber. This is where the real challenge lies.
When things heat up, they expand, adding pressure. When things are pressurized they heat up, so there is a constant control problem going on inside the press. Highly computerized systems control this battle and if you’re lucky, in two to three weeks you will have diamond crystals instead of graphite!
This is essentially what happens in a diamond press or 300 miles below the surface of the earth. Given the right conditions, super concentrations of carbon, one of earth’s most common elements, just wants to be diamond.
CHEMICAL VAPOR DEPOSITION (CVD) METHOD
There is a new upstart in the diamond making field that is in fact older than the 1954 success announced by General Electric. It is called CVD or Chemical Vapor Deposition.
Theoretically, this process defies all the laws of chemistry taught in college. Mathematically, a diamond will form at certain pressures and at certain temperatures. If these are not achieved, you cannot make diamond. But wait, you can fool Mother Nature!
The CVD method does not use high pressure but instead uses extreme heat. Methane gas, (one part carbon and 4 parts hydrogen) is pumped into a chamber as hot as the sun. This is called a plasma reaction and is accomplished with microwaves. The extreme heat breaks up the methane molecule and allows the super heated carbon to rain down on thin diamond seeds. If all goes well, and it doesn’t all the time, you will end up with about 40 diamonds that look like hockey pucks but smaller. These are 100% diamond, single crystals, identical to natural diamond. The beauty of this process is you are not limited to how much carbon you started with as in HPHT, but you can continue to pump in more and more gas, with only the growth chamber size your limit.