Once you have chosen the style of the ring, the next decision is the diamond itself. When selecting a diamond, the most important rule of thumb is to choose the finest diamond you can afford. The best way to determine a diamond's quality is to measure it according to the 4cs: Cut, Clarity, Color, Carat Weight
Cut refers not to the shape of the diamond, but to the angles, proportions and faceting arrangements of the stone. It is perhaps the most important of the 4cs because it is what releases the diamond's brilliance. A well-cut diamond will internally reflect light from one facet to another and disperse and reflect it through the top of the stone. Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom, resulting in less brilliance. The shape of a diamond is its outline. Common shapes for a diamond are round, emerald, oval, princess, radiant, pear, marquise and heart. The faceting arrangement, along with the outline of the diamond, results in the diamond's visual brilliance. A diamond cut is classified as Excellent, Very good, Fair and Poor. The style and shape of a diamond are easy to see. The style of a diamond refers to the pattern of the facet arrangement. There are three basic types of faceting arrangements -- brilliant-cut (round, oval, pear, marquise, heart), step-cut (emerald, baguette) and mixed-cut (princess, radiant). Brilliant and mixed-cut diamonds have a sparkly brilliance while step-cut diamonds have a mirror-like brilliance. The shape of a diamond is its outline. Common shapes for a diamond are round, emerald, oval, princess, radiant, pear, marquise and heart. The faceting arrangement, along with the outline of the diamond, results in the diamond's visual brilliance.
Color refers to the degree to which a diamond is colorless. Color in a diamond is the result of traces of other elements, which mix with carbon during the diamond's formation. White diamonds are color graded on a scale that begins with "D" indicating a total colorlessness, progressing down the alphabet for lower qualities. While diamonds tinged with yellow or brown are less desirable. Diamonds of vivid colors such as Canary Yellow are rare and today are highly valued.
Clarity is an indication of a diamond's purity. In all diamonds, except the most rare, tiny traces of non-crystalized carbon (the element from which a diamond is formed) can be trapped during the crystallization process. These internal 'inclusions' appear as tiny crystals, clouds or feathers. The presence of some inclusions does not diminish the diamond's beauty or endanger its durability. Most cannot be seen without powerful magnification. Clarity is based on the quantity, size, position, nature, color and relief of inclusions in a diamond. There are 10 clarity grades, where each grade represents a range. Clarity is determined by a trained grader, using 10-power magnification.
Carat weight is the gemologist's universal measurement of a diamond weight (not how big it is) and is the easiest of the 4cs to determine. Diamonds are weighed when they are loose or free from any mounting or setting. A carat weighs 0.02 grams or 1/142 of an ounce. And one carat is made up of 100 units called points. Therefore, a diamond of 75 points weighs 3/4 of a carat, and 50 points, 1/2 of a carat. It is important to know that two diamonds of equal weight can have very different appearances because of their cut, and different values because quality is still determined by cut, color and clarity.