Cut

The cut of a diamond is the only characteristic attributed by man, it
determines both the shape and life of the stone. When a diamond is cut to
good proportions, light will reflect from one facet to another, dispersing
through the top of the stone, resulting in a display of fire and
brilliance. An experienced diamond polisher can determine the shape that
a finished diamond will be by examining the rough stone, always minimising
waste and maximising clarity.