Lab grown diamond were explored as early as the 18th century, but it was not until the 20th century that the development of thermodynamics and high-temperature and high-pressure technology made it possible to lab grown diamond 40 small diamonds were successfully synthesized for the first time in 1953 by the Swiss Engineering Company (ASEA) using a pressure ball device, and in 1955 by General Electric (GE) in the USA using a pressure belt device to synthesize small particles off of diamonds.
As a result of the technological advancement of man-made diamonds, the quality of man-made diamonds is now very high. From the naked eye alone, we can no longer tell whether a diamond is lab grown diamond or not.
As HPHT method involves using metal catalyst, it is hard to avoid some metals entering the crystal during growing process, so HPHT diamonds might be magnetic. And if the magnetism is too strong, diamonds will not be able to pass the diamond teste. Because CVD diamonds are formed by mere gas, they can be produced without magnetic and are able to pass the diamond tester pen.