Community: Library

Diamonds

Diamonds are valued based on four criteria: color, cut, clarity, and carat.

The color of the diamond is usually graded. However, scales are not uniform: a "D" may be the best color for one scale, but not for another. Make sure you know how a particular scale and grade represent the color of the diamond you’re considering.
The cut of a diamond is determined by the craftsman. When a diamond is cut to good proportions, light will reflect from one mirror-like facet to another and disperse through the top of the stone. The better cut a diamond, the more brilliant it is.
The clarity of the diamond is usually graded. However, scales are not uniform: a "D" may be the best clarity for one scale, but not for another. Make sure you know how a particular scale and grade represent the clarity of the diamond you’re considering.
The size of a diamond is represented by the carat. Each carat is equal to 100 points.

Diamonds are weighed in carats and can be described in decimal or fractional parts of a carat.

If the weight is given in decimal parts of a carat, the figure should be accurate to the last decimal place. For example, ".30 carat" could represent a diamond that weighs between .295-.304 carat.
If the weight is given in fractions, the retailer should disclose two things: that the weight is not exact, and the reasonable range of weight of the diamond. For instance, a diamond described as ½ carat could weigh between .47 and .54 carat.

Diamonds may be treated to improve their appearance.

Fracture filling conceals cracks in diamonds by filling them with a foreign substance. The filling may not be permanent.
Lasering involves the use of a laser beam to improve the appearance of diamonds that have black inclusions or spots. Lasering is permanent.
Coloring involves the use of artificial means to color the diamond. Coloring may not be permanent.

Imitation diamonds, such as cubic zirconia, resemble diamonds in appearance but are much less costly. Certain laboratory-created gemstones also resemble diamonds and may not be adequately detected by the detectors originally used to identify cubic zirconia.

Diamonds are "flawless" or "perfect" only when they have no flaws, cracks, inclusions, carbon spots, clouds, internal lasering, or any other blemishes or imperfections when viewed under 10-power magnification by a skilled grader.

Diamonds are "brilliant", "brilliant cut", or "full cut" only when they are round diamonds that have at least 32 facets plus the table above the girdle (the rim around the diamond) and at least 24 facets below.

Guidelines:

Identify whether the stones are natural, laboratory-created, or imitation.
Provide the measurements of the gemstone. Include the number of karats, points, and millimeters.
Describe the 4Cs (color, cut, clarity, and carat) as fully as possible.
Describe fully the enhancements made to the stone. Specify whether the enhancements are permanent and if the treated stone requires special care.

Source:

All That Glitters...The Jive on Jewelry, August 1998, FTC
Guides for the Jewelry, Precious Metals, and Pewter Industries, FTC
In the Loupe: Advertising Diamonds, Gemstones, and Pearls, August 1998, FTC