HPHT stands for high pressure, high temperature. The same conditions can grow a diamond in a laboratory or treat a natural one to change its color.
In more detail
When HPHT is a treatment, it is permanent and must be disclosed. GIA grades an HPHT-treated diamond on a full grading report, never a Dossier.
On a grading report
For HPHT color treatment, GIA adds an asterisk to the color grade and explains it in Comments. It inscribes TREATED COLOR on the girdle. For HPHT growth, the stone gets a lab-grown report; IGI can note HPHT as the growth method.
Related terms
- CVD: CVD, chemical vapor deposition, is one of the two usual methods for growing diamond in a laboratory. The other is HPHT.
- Color treatment: A color treatment is any process that changes a diamond's color, such as HPHT processing or coating.
- Asterisk after the color grade: An asterisk (*) after a GIA color grade means that the lab detected a color treatment. Comments explains what it is.
- Laboratory-grown diamond: A laboratory-grown diamond is a diamond that people grow with machines, by HPHT or CVD. It has essentially the same composition, crystal structure and properties as a natural diamond.
- Treatment: A treatment is any process, other than cutting and polishing, that changes a gem's color or apparent clarity. Anyone who sells a treated gem must disclose the treatment.