Gem treatments - High Pressure, High Temperature (HPHT)

High pressure, high temperature (HPHT) treatment

– Heating a diamond to high temperatures under high confining pressures to remove, or change its color.

Heating diamonds at high pressures and high temperatures can remove or lessen their brownish coloration so the gem becomes colorless. Other types of diamonds may be transformed from brown to yellow, orangy yellow and yellowish green, or to blue colors by this process.

High pressure, high temperature treatments can alter the atomic structure of some types of diamonds, in this case removing the brownish coloration and turning the diamond colorless.

1. Durability factors – HPHT treatments are considered stable and permanent to normal jewelry handling conditions.

2. Detectability – Difficult to identify, even by seasoned gemologists. If suspected, only a qualified gemological laboratory can confirm the treatment.

3. Encountered in the trade – Occasionally in colorless diamonds, more readily in some colored diamonds.


Source: Robert Weldon,

To learn more about gem treatments see also:

- An introduction to Gem treatments

- Gem treatments - Bleaching

- Gem treatments - Surface Coating

- Gem treatments - Lattice Diffusion

- Gem treatments - Laser Drilling

- Gem treatments - Irradiation

- Gem treatments- Impregnation

- Gem treatments - Heat treatment

- Gem treatments - Fracture or Cavity Filling

- Gem treatments - Dyeing

4. Special care requirements – Other than normal care considerations used for most jewelry, there are no particular instructions for the care and handling of HPHT treated diamonds.