The Art & Science of the Cut
Premium and Ideal cut diamonds will have proportions simular to the illustration to your left. Proportions will vary depending on the individual diamond.
Values are taken as a percentage of the diameter of the stone (100%). Lumpy cut stones that have thick edges or girdles , heavy tops or crowns, bottoms or pavillions may appear smaller in diameter and size to the eye, then the acual scale carat weight of a well cut stone of the same size. Ideal cut diamonds hold to the strictest of proportions and are considered the most beautiful and brilliant gems!
When diamonds are cut lumpy or too deep, light will leak out the base or pavilion of the stone and create a dark gem that will not have the brilliancy  of a premium or ideal cut stone. A diamond that is cut too shallow, will allow light to leak out, creating a watery, glassy appearance with little brilliance. Ideal cut stones will return the majority of light through the top or crown of the gem, making for a magnificent diamond!
"The cutting and proportions of a diamond are components that are controlled by man and not by nature"