CUT
By cut, we are referring to two things, the first being the shape of the diamond. By this we mean round, marquise, pear, oval, princess, emerald, heart or trillion. Many people think fancy shaped diamonds cost more. In most cases, it is exactly the opposite. Many fancy shape diamonds actually cost less than a round.
When a gemologist talks about cut, what is really being referred to is quality of proportions. Cut, more than any other quality aspect, gives the diamond its sparkle. A diamond gets its brilliance and scintillation by cutting and polishing the diamond facets to allow the maximum amount of light that enters through its top to be reflected and dispersed back, also through its top.
As you can see , when all the angles are correct, the light that enters is dispersed back through the diamonds top facets. When a stone is cut too shallow or too deep, the light that enters through the top is allowed to escape through the bottom and does not allow the maximum beauty of the diamond to be realized
