1 - Carat - Weight

The carat measures the weight of a diamond. One carat is equivalent to 200 milligrams. In general, the heavier the diamond, the more precious it is. For very large diamonds, the term "kilocarat" is sometimes used, equivalent to 1,000 carats. Diamonds weighing several kilocarats are rare and highly sought-after. It is important to note that diamonds slightly smaller than round weights (for example, 1.90 carats instead of 2 carats) can offer better value for money while looking similar.

2 - Cut - Size

The cut of a diamond is crucial to its brilliance and sparkle. It refers to the way in which the diamond has been cut and shaped, including proportions, symmetry and finish. A good cut will allow light to reflect and refract inside the diamond, maximising its brilliance. Diamonds can be cut in a variety of shapes, such as round, princess, emerald or oval. The quality of the cut is often graded on a scale from "Very Poor" to "Excellent".

3 - Color - Couleur 

The colour of diamonds is a determining aspect of their beauty and value. Diamonds are classified according to a colour scale ranging from D (colourless) to Z (yellow or brown). Colourless diamonds are the rarest and most valuable. Even subtle nuances can affect the value of a diamond, so it's crucial to pay attention to this characteristic. Some brightly coloured diamonds such as pink, blue or green are also highly sought-after and can have a higher value, regardless of the standard scale.

4 - Clarity

Purity refers to the presence of inclusions or flaws within the diamond and imperfections on its surface. Diamonds are graded on a scale from 'Flawless' to 'Included'. Inclusions are natural imperfections that can affect a diamond's brilliance. A high purity diamond is generally more valuable, but it is also important to note that some inclusions may be invisible to the naked eye and do not affect the overall appearance of the stone.