What are HPHT treated diamonds?
HPHT stands for high pressure, high temperature, and is a laboratory process which can be used to change the color in some gem diamonds. In the 1990s, scientists began to experiment with ways to modify diamond color using the high temperature and high pressure technique. HPHT treatment can change the color of certain Type IIa diamonds, making them colorless, pink or blue. HPHT can also change certain Type Ia diamonds to green, yellowish green, or yellow. Type IIa diamonds are very rare in nature. They make up less than 2 percent of diamonds mined. On the other hand, type Ia diamonds are the most abundant kind of diamond in nature.