High Pressure High Temperature (HPHT)

GE developed the High Pressure High Temperature or HPHT process to enhance the tinted color of some diamonds especially when it is still in its rough state. Through this treatment, a significant improvement in the diamond’s clarity can be observed, thus improving its grade and its price value as well. Approximately 1% of all gem quality diamonds are suitable for this process.

High Pressure High Temperature chamber

When these diamonds placed inside the HPHT chamber or furnace are exposed to very high temperature and very high pressure, similar with the temperature and pressure under the Earth while the diamond is developing, the diamond’s molecular structure is altered producing a whiter color and the diamond changes from brownish tint to colorless or near-colorless. This process is also considered as permanent treatment and is almost always impossible to detect.

“Before and After” HPHT procedure. The diamond’s natural brown tint was removed
by permanently altering the molecular structure of the diamond

The Gemological Institute of America uses very expensive equipment to verify if a diamond has indeed gone through HPHT treatment. Once verified, a note is included on the diamond’s grading report for perusal or as reference.


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