The proportion of a polished diamond determines its "brilliance and fire".
The cut of a diamond refers to not just the shape but the arrangement along with symmetry of facets that determine how light will interact within the stone.
The round brilliant cut is the most popular amongst customers.
Proportion characteristics include: the size of the table, the crown angle and height, the pavilion angle and depth, the girdle thickness, and the culet-size.
Every diamond is given a proportion grade between excellent, very good, good, and fair.
The finish grade of a diamond evaluates skill of a polisher.
Finish grade deviations originate not only from careless cutting, but also from the consideration to minimize weight loss.