The 4Cs

The quality and price of a cut diamond are determined according to the 4Cs rule:

Carat, Cut, Colour & Clarity

1. Carat


The "carat" is a unit of mass used for gemstones. The word "carat" comes from the Arab word Kharoub, as the Carob tree (and specifically carob seeds) was used as a benchmark in terms of weight.

Former diamond dealers still call a 1-carat diamant a "four-grain diamond", i.e. it weighs the equivalent of 4 carob seeds.

In 1907, the metric carat was established as being equal to 200 mg or 5 carats = 1 gram.

2. Cut

Diamonds are cut into an infinite number of different cuts, the main ones being:

  • Round brilliant
  • Princess cut
  • Oval
  • Pear shaped
  • Radiant cut
  • Marquise
  • Heart shaped
  • Emerald cut
  • Cushion cut
  • Trilliant

The cut of the diamond is graded from "excellent" to "poor", according to the criteria for proportion, symmetry and polish

3. Colour


Diamonds are colourless or almost colourless, but they are colour graded from D (absolutely colourless) to Z (noticeable colour).

These are followed by fancy coloured diamonds, the most common of which are brown, yellow, green, and ending with the rarest, such as blue or red.

Maison Vernain Auguste - diamond-colour

4. Clarity or purity


Diamonds are clarity graded from Flawless with no inclusions (FL) to included3 (I3) with numerous inclusions.

Maison Vernain Auguste - diamond-clarity