High Pressure High Temperature method replicates the natural process of diamond formation under the Earth’s crust like a giant pressure cooker.
High-Pressure High-Temperature, or HPHT, recreates a diamond's natural growing environment found deep within the Earth. The machines used have the ability to build up the pressure of almost 60,000 atmospheres and temperature of 2,500 degrees Celsius.
The growth cell contains all the elements needed to grow a diamond, including a seed, highly refined graphite and a catalyst mixture consisting of metals and powders. The cell is placed in the center of the HPHT chamber. Consistent temperatures reaching 1,300 degrees Celsius and more than 50,000 atmospheres of pressure are applied. The catalysts inside the cell are the first to react to the added heat and pressure and change from solid to molten form.
The molten catalyst solution causes the graphite within the cell to dissolve. Once all the required conditions are met, the cooling process begins. This process takes place over several days and allows the carbon atoms to build upon the seed. The cell is removed from the HPHT machine once the growth cycle is complete. The new rough diamond is extracted and cleaned in preparation for final cutting and polishing.
The entire HPHT growing process requires an incredibly controlled environment to produce a gem-quality diamond. Any shift or change during growth can cause the diamond to stop growing or can create inclusions that result in unusable diamonds. Every diamond must complete the entire growth cycle before the machine can be opened. It is only after the HPHT chamber is opened that we can see the finished rough diamond and its color, clarity, and size.