What is HPHT diamond?

  Chemical Vapor Deposition. Chemical vapor deposition uses one or more gases to chemically react on a heated solid substrate and is coated with a solid film. The diamond is a natural diamond bare stone as the mother stone, using high-purity methane, plus hydrogen, nitrogen and other gases to assist, in a microwave oven under high pressure, so that the same carbon molecules in methane as diamond continue to accumulate on the rough diamond. Layer by layer, it can form transparent diamonds up to 10 carats. 

  In order to make CVD diamonds grow smoothly, the carbon source is often methane that already has a diamond structure. Methane can be regarded as a monoatomic diamond extruded with hydrogen. The quality of this "grown-up" diamond is almost the same as a natural diamond, making it hard to distinguish with the naked eye. At present, this kind of CVD synthetic diamond can be distinguished from natural diamond by observing its phosphorescence performance under short-wave ultraviolet, and a simple preliminary screening can be performed.