Since a Round Diamond is completely symmetrical and capable of reflecting nearly all the light that enters, it is the most brilliant of all diamond shapes. Fancy Shape Diamonds - or any diamond shape that is not round - follow different proportion guidelines.
 
Without the benefit of a round refractive pavilion, light can filter directly through an area in a Fancy Shape Diamond, creating a window that you can see right through. In some diamond shapes, this area takes on the shape of two offset triangles, creating an effect called a "Bow-Tie". The more prominent the "Bow-Tie", the less brilliant the diamond. An "Ideal-Cut" Fancy Shape Diamond has no noticeable "Bow-Tie".