The cutting and proportions of a diamond are components that are controlled by man and not by nature. It is what unlocks the beauty and brilliance of the gem, and is what will set one diamond apart from another. Standard cut diamonds have 58 facets, or cuts that help direct the light through the stone. When a gem is properly proportioned, the light entering through the top or crown is bent and reflected inside the stone and returned through the top creating a magnificent gem!
There are three factors that make up the "Sparkle" or life of a diamond.
Brilliancy is the ability of the gem to return the maximum amount of light to your eyes. Think of two light bulbs, one 40 watts the other 100 watts. The higher the wattage, the brighter or more brilliant the diamond. The second component is scintillation, which is the breakup or sparkle, dancing flashes of light you see as the stone is rotated. The third and last component is dispersion, the ability of the gem to break up white light into its spectral colors. Theses are the hints of blues, red, yellows, and many other colors you see flashing in the stone. Symmetry and Polish, or how precise the facets are fashioned on the stone, fine polish and finish of the gem all help determine the maximum amount beauty in your stone.
The Art & Science of the Cut