are four main factors determining colorless and near-colorless
diamond's value. These attributes are size (carat weight), cut,
color, and clarity. Collectively, they are often referred to
as the "Four C's."
A diamond's weight is expressed in carats. Carat weight is the easiest of the four C's to determine. To get the exact weight, however, the diamond must be loose. One carat is divided into 100 "points" so that a diamond of 50 points is described as a half carat in size, or 0.50 carat. Within common weight ranges, there is little or no variation in per-carat price.
The cut of a diamond is related to its proportion. Many cutters choose to sacrifice some of the diamond's beauty to produce a stone that is a larger carat weight. Cut, more than any other quality aspect, gives the diamond its sparkle. A diamond gets its brilliance and scintillation by the cutting and polishing of its facets, allowing the maximum amount of light that enters through its top to be reflected and dispersed back through the top. With proper cutting, the light passes through the top, bounces off the sides, and then travels back out the top, giving the diamond optimum brilliance. If the diamond is cut too deep, light passes through the side of the diamond. If the diamond is cut too shallow, light passes through the bottom of the diamond, also inhibiting maximum brilliance.
Two popular overall proportion indicators are Total Depth Percentage (D%) and Table Percentage (T%) . D% is the diamond's depth expressed as a percentage of its width (average diameter for rounds). T% is the diamond's "table" width expressed as a percentage of its overall width (diameters for rounds). Round diamonds with cutting proportions within the range generally considered attractive have depths from 55 to 63 percent. The table size of most round diamonds lies between 56 and 64 percent . With non-round shapes ("fancy" shapes), much greater proportion variations are encountered. In most fancy shapes, higher D% and T% are more common and are dependent on width to length ratios.
Diamonds come naturally in almost every color of the rainbow. However, most people prefer diamonds in the white range. Colorless diamonds are more valuable, because they are rarer and their lack of color, or whiteness, in a diamond that allows the light to pass effortlessly through the stone and disperse that beauty back to the observer. The color grading scale established by the GIA (Gemological Institute of America) varies from D (totally colorless) to Z (light yellow). D through F are virtually colorless. G, H and I diamonds appear colorless when mounted. J, K and L diamonds look very nearly colorless, but you can see some color in larger stones. Beyond M, most people can see color pretty easily. The color of the metal in a mounting can either mask or enhance the diamond color. Yellow gold makes slightly yellow or brown diamonds appear more colorless. White mounting (gold or platinum) makes the color more perceptible.
Fluorescence is not formally a color grading term. Many diamonds glow when exposed to light which contains relatively high amounts of ultraviolet. This is due to a natural interaction between the light's energy and the atoms in the diamond. Some diamonds (about 10%) fluoresce strongly enough so as to be somewhat noticeable in regular (incandescent) light. Generally, for very light yellow color diamonds, fluorescence is considered to be beneficial since it makes the diamond appear whiter.
The fewer the inclusions, the rarer and more valuable your diamond will be. To determine a diamond's clarity grading the stone must be examined under a 10X magnification by an educated eye. Small inclusions make every diamond unique and are nature's fingerprints. Generally, they do not mar the beauty or endanger the durability of the diamond. In most cases, if a diamond is SI2 or above, the inclusions are not easily visible to the unaided eye. Without magnification, you may never see these inclusions.