There are mainly the following methods for laboratory synthetic diamonds:

HPHT Method (High Pressure High Temperature Method): This method was one of the first to create diamonds in the laboratory. In this method, seeds of diamond crystals are placed in a carbon source under high temperature and pressure, and through a process of dissolution and recrystallization, diamonds are synthesized within days or weeks.

CVD method (Chemical Vapor Deposition): This method uses chemical reactions at high temperatures to deposit diamond crystals on a crystal substrate. Usually, methane and hydrogen are used as reaction gases, and the reaction is carried out in a vacuum chamber to form diamonds.

THPHT method (Pyrolysis High Pressure): This method uses high pressure, high temperature and high speed pyrolysis to convert carbonaceous materials into pure diamonds.

Explosion method: This method uses the high temperature and high pressure environment generated by the explosion to generate diamond nuclei in carbonaceous materials, and then synthesize them into diamonds under high temperature and high pressure.

All of the above methods can produce high-quality artificial diamonds in the laboratory, among which HPHT and CVD methods are the two most commonly used methods.