CUT

Cut is the most misunderstood of the 4 Cs. It is often wrongly thought of as the shape of the stone. This confusion exists because, of course, the raw material must be cut into a shape, and the confusion increases because shapes of diamonds are given names like Round Brilliant Cut, Oval Cut, Emerald Cut, and so forth. Cut, when speaking of one of the four qualities that give diamonds their value, actually refers to the geometric proportions of the gem. The geometric proportions are important because a diamond is a prism that refracts, or bends, light rays, breaking white light into the colors of the rainbow. It is this refraction that unleashes the color spectrum in a way that gives a diamond its fire. The optical proportions must be exact in order to achieve maximum brilliance.

Light refraction
Light enters from the top of the diamond, is funneled downward where it strikes facets at the bottom, then is refracted to other facets of the stone again and again as it works its way back up, until it leaves the stone at the top and enters the eye of the observer. Cutting proportions are extremely precise to achieve the best effect.

Proper Proportion
Many stone cuts lack proper proportion and refraction of light. The cut may be too heavy or too deep, allowing light to escape through the lower pavilion. If the cut is too shallow, light rays leak away at the bottom. Too much weight above or below the girdle affects the brilliance, and the stone lacks fire.

CARAT WEIGHT

Diamonds and other gemstones are measured by carat weight. A carat is 1/5 of a gram, or 200 milligrams. (The word carat comes from the carob bean, which weighs about 1/5 of a gram and was used as a measure in earlier times.) Stones lighter than a carat are measured in points. There are 100 points in a carat. A point is equal to .01 ct.

In general, most shoppers prefer a diamond of at least one carat. Consequently, stones that are fractionally smaller than one carat (i.e., .98) can be considerably less expensive. It's worth checking out.

CLARITY

Clarity is the term used to describe the internal quality of a gem. A trained expert examines the diamond for inclusions, cracks, spots, clouds, or any other blemish or imperfection of any sort. Usually blemishes cannot be seen with the naked eye but can be detected under 10-power magnification.

The Gemological Institute of America (GIA) recognizes 10 grading levels for clarity. Other qualities being equal, the lower the clarity grade, the less valuable the stone.

* IF - Internally Flawless
Free of flaws, cracks, spots, clouds, or any other blemish or imperfection of any sort when examined under proper light by a trained eye with the aid of a diamond eye loupe or other magnifier with a magnification of at least 10 power.

* VVS1- Very, Very Slightly Imperfect (1)
The gem may have a very tiny pinpoint of included material, cloud, polishing line, or faint knot line, but only one of these blemishes and it is very faint to a trained eye under 10X magnification.

* VVS2 - Very, Very Slightly Imperfect (2)
Inclusions may be the same as for VVS1, but slightly larger and more numerous. They are still very hard to see.

* VS1 - Very Slightly Imperfect (1)
The gem may have minute internal cleavage or fracture (feather) near the girdle, or it may have any of the above blemishes, slightly larger but still fairly difficult to detect under 10X magnification.

* VS2 - Very Slightly Imperfect (2)
Any of the above inclusions are more easily visible under a 10X loupe. An included crystal or other small blemish may be seen through the crown.

* SI1 - Slightly Imperfect (1)
The diamond has a cleavage fracture or any blemish or combination of blemishes not visible to the unaided eye but easily seen under 10X magnification. A small dark spot in the center of the stone or a larger white flaw toward the edge would be graded SI.

* SI2 - Slightly Imperfect (2)
The diamond has slightly larger inclusions than grade SI1, but they still are not visible to the naked eye when the stone is face up.

* I1 - Imperfect (1)
Inclusions are just visible to the eye without a loupe.

* I2 - Imperfect (2)
Inclusions are easily seen with the unaided eye.

* I3 - Imperfect (3)
This grade denotes a badly flawed diamond with cleavages, fractures, large clouds, and dark spots large enough to block light passage and destroy brilliancy. This grade of diamond would be inappropriate for jewelry.

Excessive inclusions or fractures not only make the diamond unattractive, but may weaken its strength so it is more likely to crack. However, flawless diamonds are extremely rare in nature. One expert points out that no two diamonds are alike, and that inclusions in a particular stone are like its fingerprint, identifying it among all others.

COLOR

The finest and most expensive diamonds are totally without color, like a drop of distilled water. The rainbow hues a diamond flashes derive from the light it separates into the colors of a spectrum. Diamonds of lesser quality have a yellowish or brownish cast.

Judging color is a job that can be performed only by experts with proper gem lab equipment. To grade color, the gemologist places the diamond under white light that is constant and free of ultraviolet rays. The stone is placed table down (that is, top down) and viewed through the pavilion. It is more difficult to judge color if the stone is already mounted.

The tested diamond is compared to a set of five master stones whose colors have been accurately graded and certified by the Gemological Institute of America.

The GIA color grading scale ranges from D through Z. (A, B and C are not used to avoid confusion with other grading systems that use only those three letters.)

* D - E: The diamonds are colorless.
* F - I: The diamonds are near colorless. Small stones appear colorless when mounted, but large stones appear tinted to the trained eye.
* J - L: Slight traces of color are apparent in mounted stones only to the trained eye.
* M - Z: Mounted stones will display a yellowish tint, even to the untrained eye.

The gemologist assigns the stones a specific letter grade. All other things being equal, the lower the color grade, the lower the stone's value.

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