The most used cut is the round "brilliant": 58 facets, or rather 57 + 1, considering 1 as sanding the tip of the lower cone, called a Culet. This is the best cut that brings out the phenomena of refraction and reflection of light in a diamond and is therefore the most appreciated and accepted. The shape and the perfect cut gain importance in determining the value of a gemstone. There are specific proportions between the dimensions of the various components (board, crown, pavilion, belt) that need to be observed to achieve the maximum results. The classification of the cut has four parameters:

VERY GOOD: great cut, without any derogation to tolerances

GOOD: good, with slight deviations to tolerances (less than 5%)

MEDIUM: medium, with notable deviations to tolerances (less than 10%)

POOR: poor, with serious deviations to tolerances (in excess of 10%).

If a diamond has an ideal cut, the light rays coming from all directions are diverted towards the center of the stone and reflections across the top with a blaze of light. If a diamond does not have the right cut,  the light will eventually "get lost" sideways (cutting too high) or the underside of the stone (cut too low).