- Hardness - the measurement of resistance to permanent deformations.
On the Mohs hardness scale, the hardness of a diamond is a 10, the hardest rating of all.
- Heart Cut See Shape.
- HPHT - High Pressure High Temperature treatment process. See Color Enhancement.
- HRD - Belgian-based certification lab.
- Hue the basic impression of a color; the aspect that gives color its identity.
In colored diamonds, a lab might give a diamond one or two or three color grades. For example, a diamond might be a fancy yellowish, brownish orange. The latter color is the most dominant hue and the one that affects the value the most.