- Hardness - The measurement of resistance to permanent deformations.
On the Mohs scale of mineral hardness, the hardness of a diamond is a 10, the hardest rating of all. Developed in the 1800s by Friederich Mohs, the scale ranges from 1 (softest) to 10 (hardest). It measures the hardness of the stone and its resistance to scratching.
- Heart Cut - See Shape.
Designed to resemble the international sign of love and affection, the love heart, the modified brilliant cut heart shape has grown in popularity over the past few years. The first record of a heart shaped diamond dates back to the 1500s, when Mary Queen of Scots wore a heart shaped diamond ring. Elizabeth Taylor was famously gifted a large heart shaped diamond ring by Richard Burton in the 1970s and Lady Gaga’s engagement ring from Taylor Kinney was a heart shaped diamond.
Symmetry is particularly important for heart shaped diamonds, as both side of the stone should be identical and the cleft should align with the pointed tail of the diamond. Larger sized heart shaped diamonds are preferable, as the smaller stones can be mistaken for a round diamond. Buying a heart shaped diamond of 0.50ct or larger is therefore recommended.
- HPHT - High Pressure High Temperature treatment process.
High Pressure, High Temperature (HPHT) is a color treatment performed on some diamonds to improve their color grade. It attempts to recreate the conditions under which the diamond was formed, deep in the Earth under huge amounts of heat and pressure. It can only be used on high clarity grade diamonds (VS1 – FL) as the high pressure and heat applied can cause stones with more imperfections to fracture.
It is the only permanent color treatment process for diamonds. And while it improves the color of the diamond, it does have a negative effect on the value of the stone. The reason being is that any artificially altered stones of a specific color grade, are not as rare as natural, untreated stones of the same color grade.
Developed in the 1950s, this treatment allows companies to purchase cheaper stones and sell them for much higher prices once they have undergone HPHT. The GIA has spent considerable energy researching HPHT treated diamonds and how they can be detected.
See Color Enhancement.
- HRD - Belgian-based certification lab.
HRD (in Dutch: Hoge Raad voor Diamant) translates to High Diamond Council and is based in Antwerp, Belgium. Founded in 1973, this diamond grading laboratory is often used as the alternative to the GIA in Europe. HRD offers micro laser inscriptions and all diamond grading certificates issued post 2005 are available on their online database. Their diamond grading certificates include the 4 C’s of the diamond along with the polish, symmetry and measurements of the stone. Each certificate has it’s own unique number, specific to the stone.
- 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.