The HPHT method involves a small diamond seed being placed in a chamber with a mixture of gases and heated to high temperatures and placed under immense pressure. The CVD method involves using a plasma torch to vaporize a carbon-containing gas, such as methane, and the carbon atoms deposit onto a substrate forming a diamond crystal. Both methods replicate the conditions that occur in the Earth's mantle, where natural diamonds form, but use different methods to create diamond crystals.