Published on the Italian Gemological Review, issue N°3, Jan 2018
In 1999, General Electric (GE) announced that it had developed a high-pressure/high-temperature (HPHT) treatment to improve the color of type II diamonds from brownish to almost colorless. Although the process was restricted to a limited percentage of diamonds, the discovery threw the market into a panic; almost simultaneously the gemological community was activated to develop a method for the identification of the treatment and it was immediately clear that the task was not so easy to accomplish. The standard methods did not provide for any useful information: all the advanced techniques were put at work and the most promising was the photoluminescence spectroscopy. Since then this methodology of investigation turns out to be the architrave on which the most widespread protocols of investigation on diamonds are grounding in gemological laboratories all over the world.