cut of a diamond determines how well it reflects light. This reflection
is responsible for the gems brilliance or sparkle.
Skilled professionals cut the stone to mathematically exact proportions
so as much light as possible reflects
from each of its mirror-like facets out the top of the diamond.
The diameter and depth of the gem affect how light travels within
it and how light exits in the form of brilliance.
If the cut is too shallow, light escapes out the sides and the diamond
If the cut is too deep, light is lost out the bottom and the diamond
appears dark or dull.
width of the diamond through the girdle
largest facet at the top
top part from the girdle to the table
narrow band around the widest part of a diamond
bottom part from the girdle to the culet
facet at the bottom tip. The preferred culet is not visible
to the naked eye (graded "small" or "none")
height from the culet to the table
two most important numbers to be looking for when looking
for great cut are the
depth percentage and the table percentage.
-- Depth percentage is the depth of the diamond (table
to culet) divided by the width of the diamond. The higher
the number, the deeper the stone. The lower the number the
shallower the stone. Table percentage is the length of the table divided
by the width of the diamond. The higher the number, the
bigger the table looks. The lower the number, the smaller
the table looks.
-- Out of Round: It is interesting to note that "round"
diamonds are usually not perfect circles.
The length and width measurements for a round are both diameter
and will be different for an out-of-round shape.
The following charts provide a summary of the top cut grades for
round diamonds by the major grading laboratories.