COLOR:
Diamonds are found all over the globe in a wide range of colors, from completely colorless (the most desirable) to slightly yellow, to brown. “Fancy colored diamonds” come in much more intense and extreme colors such as yellow and pink, but these are graded a different way. The diamond color grading system uses the letters of the alphabet from D through Z, with 'D' being absolutely colorless and therefore the rarest and most valuable, and 'Z' having the most color within the normal range, and being the least valuable, all other factors being equal. A diamond's color is determined by looking at it under controlled lighting and comparing them to the Gemological Institute of America's color scale, which is based on a set of diamonds of known color.
A diamond's color is easier to determine when it is not mounted in a setting. Settings can affect the tint or shade of a diamonds. This is more evident in yellow gold settings, and less so in white gold and platinum settings. Even a trained professional can't always tell the difference between close grades of color in a diamond if it is still mounted in a setting.
Diamonds with a color grade of D, E or F are considered colorless; G, H, I and J are near colorless; K, L and M have a faint yellow tint; N, O, P, Q and R have a very light yellow tint and S, T, U, V, W, X, Y and Z are light yellow. A diamond that is a D color is absolutely colorless, and is therefore the most valuable. Here are some examples of different colors in a diamond:
CLARITY:
This refers to the number, position and size of the inclusions that occur naturally inside diamonds. The fewer and less obvious the inclusions, the more valuable the diamond. Here is an illustration that shows the clarity grading scale that has been established by the world's foremost authority on diamonds, the Gemological Institute of America (GIA). Note: Diamonds are shown under 10X magnification):
A diamond's clarity is measured using a jeweler's loupe (a small magnifying glass used to view gemstones) under 10-power magnification. The FTC requires all diamond grading be done under 10-power magnification; any inclusions not detected under this magnification are considered to be non-existent.
CUT:
Cut is the result of a craftsman's skill in transforming a rough diamond into a breathtaking gem. A diamond has facets that allow light to enter it, become refracted, and exit in a rainbow of colors. So it follows that a better cut diamond does a better job of dazzling us with its beauty. Here's the key to achieving maximum fire with a round, brilliant diamond:
As you can see, the diamond with the correct proportions does a more effective job of refracting light out the top of the stone to your eye. The less-than-ideal cut diamonds allow some light to become lost out the bottom.
CARAT WEIGHT:
A diamond's weight is measured in what is known as a 'carat', which is a small unit of measurement equal to 200 milligrams.
Carat is not a measure of a diamond's size, since cutting a diamond to different proportions can affect its weight. (The word 'Karat' is used to express the purity of gold, and is not used in relation to diamonds.)
The most important thing to remember when it comes to a diamond's carat weight is that it is not the only factor that determines a diamond's value. In other words, bigger does not necessarily mean better. All four Cs-Cut, Color, Clarity and Carat Weight must be balanced in order to arrive at a diamond that fits your budget.
The word carat actually comes from the word carob (as in carob seeds), which is how ancient cultures measured the weight of diamonds on their scales. In 1913, however, the weight was standardized internationally and adapted to the metric system.
Although they can be measured when mounted in jewelry, diamonds are most accurately weighed when they are not mounted in a setting. In fact, gemological laboratories such as the Gemological Institute of America (GIA) and American Gemological Society (AGS) will only grade diamonds that are unmounted. A diamond grading report will tell you the exact carat weight, to the nearest hundredth of a carat, for that particular diamond. Each Carat is divided into 100 parts called 'points.' So a 1-carat diamond has 100 points, a 3/4 carat has 75 points, etc. Points in a fraction of one carat are measured within ranges, so that a 3/4 carat diamond may have between .69 and .82 points and still be considered a 3/4 carat.