Four primary characteristics determine a diamond's beauty and value - The 4C's of diamond quality :

Color
Diamonds come in a range of natural colors, the completely colorless (exception white or collection) diamonds are so rare and expensive. Near colorless (white) is the second most expensive color group diamond. When these diamonds are mounted in jewelry, even expert graders may find difficult or impossible to distinguish them from a colorless diamond. Faint yellow (top silver) diamonds with a tinge of yellow are fairly common. They are less expensive than the colorless diamond and often used in jewelry. Light brown (brownies) diamonds are the least expensive color of diamonds. The promotional term for brownish-tined diamonds is champagne diamonds. Darker brown diamonds are sometimes referred to as fancy cognac. So when you choose your diamond, choose as close to colorless as possible, these diamonds will allow white light to pass effortlessly through and be dispersed as dazzling rainbow.

Cut
A good cut brings out brilliance and fire to the stone. Many people confuse the cut with the shape of a diamond. The cut refer to the arrangement of a diamond's facet so whatever shape it is, a well-cut diamond is work of a master cutter. If a stone is cut with precise angles and proportions so light will be reflected and dispersed through the top of the stone, not out the sides or bottom.

Clarity
A diamond is free from external marks called blemishes and internal features called inclusions. They are part of the diamond's history that formed within the diamond for million years. When a diamond that is free of inclusion, it is rare and very valuable. To determine a diamond clarity, by seeing the number of size and position of the inclusion under a hand magnifier called loupe.

Carat Weight
Most people are familiar with the principle, the higher the carat weights the greater diamond value. Diamond can be divided into weight categories as listed in Rapaport Diamond Report. As diamonds move up from one category to another, the price is also increased. Low-quality diamonds tend to show less of a price increased than those high qualities. The weight can also be estimated by measuring the diameter of a stone with a gauge that can correspond to the weight of the stone.