A diamond’s cut is its arrangement of facets and their proportional relationships and finish which affect the way it takes in and reflects light, hence affecting its brilliance. A properly cut diamond, regardless of its shape, scintillates with fire and light-offering maximum appeal, durability, and value.

Cut can also mean shape; proportions are the size and angle relationships between the facets and different parts of the stone. A diamond with even slight variations in proportions might appear to be too deep or too shallow - two factors that allow the spilling of light through the side or bottom of a diamond. The more successful the cutter is in balancing these considerations, the more valuable the diamond will be.