Here is a chart I hope you will find interesting. Over the past year, this chart shows the diamond color, diamond clarity and diamond cut purchases over the past year on BlueNile. Knowing what others are buying can be a big help!
Click on the image to enlarge...
Although commonly thought to refer to the size of a diamond, a carat is actually used to measure a Diamond's carat weight or mass. One carat is defined as exactly 200 milligrams (about 0.007 ounce). The point unit — equal to one one-hundredth of a carat (0.01 carat, or 2 mg) — is commonly used for diamonds of less than one carat. All else being equal, the value of a diamond increases exponentially in relation to carat weight, since larger diamonds are both rarer and more desirable for use as gemstones.
It is important to note that two diamonds with the same carat size might actually apper to be different sizes. Since carat refers to the mass of the diamond, you must also consider the cut. A diamond that is heaver on the bottom, called the pavillion, than the top might appear smaller at the same carat size as a diamond that is cut more narrow on the bottom.
Some consdier the carat the most important attribute of a diamond. You often hear people ask "How many Carats'. This is ok, but be sure to also consider the Diamond Cut, Diamond Clarity, and Diamond Color as well to make sure you are getting right diamond that she will cherish forever.
A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price as more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. Out of all colored diamonds, red diamonds are the rarest of all.
Diamonds occur in a restricted variety of colors — steel gray, white, blue, yellow, orange, red, green, pink to purple, brown, and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration, while pure diamonds (which are exceedingly rare) are perfectly transparent and colorless.
Most diamond rating agencies use the diamond color scale developed by The Gemological Institute of America (GIA), which uses a "D" to "Z" scale, grading the color of "white" (non-fancy colored) diamonds, where "D" is colorless and "Z" is yellow:
Diamonds that rate toward the colorless end of the range are sometimes known as "high-color" diamonds, and those toward the other end, "low-color" diamonds. These terms refer to the relative desirability (as demonstrated by market prices) of color grades, not the intensity of the color itself.
Quality online diamond stores, like Blue Nile, attempt to stand out by only carrying colors rated J or better, the colorless or near-colorless diamonds.
One of the most important factors in determining quality in diamonds is the cut. Cut is the only value factor that is a result of human skill. A diamond's beauty must be balanced against the inevitable loss of weight necessitated by the very process of cutting. Along with the diamond's size and shape, the minute details of workmanship play an important role in the overall beauty and sparkle of the diamond.
The top diamond grading laboratories, AGSL and the GIA, approach the grading of diamond cut slightly differently.
GIA: The majority of all high-quality diamonds have grading reports from the GIA, which does not assign a grade to the diamond cut. Instead, the GIA lists the diamond's dimensions: the width of the table, the width of the diamond, and the depth of the diamond.
AGSL: The AGSL assigns cut grades of Ideal, Very Good, Good, Fair, and Poor. The AGSL labels a diamond that meets their standard of perfect proportions, polish, and symmetry as "Cut Grade: Ideal" and is known through the diamond industry as a "000" grade. These diamonds are highly sought after and are priced accordingly.
Online Diamond Retailers, like BlueNile, have tried to simplify the cut decision by melding both the GIA and AGSL guidelines into an easy to gauge rating from Poor to Signature Ideal:
