The ABCs of gem quality diamonds come down to the 4Cs, a term that you may have seen or heard of before. The 4 Cs are cut, color, clarity, and carat, the four aspects on which a diamond’s value is judged.

So, what does this mean to you? When you are in the market for a high quality diamond -- whether loose or mounted -- the diamond’s marking for each of these aspects can significantly affect the price you pay for it.

A Cut Above

Rough diamonds look like beach glass -- pretty, but not particularly amazing. Cutting techniques that bring out the diamond’s brilliance can reduce the final gem size by half, but can increase its market value four times. Modern cutting techniques that bring out the best brilliance from a diamond were established at the beginning of the 20th century. Before, diamonds were frequently cut to maximize carat weight -- as with the "old mine cut" -- rather than light diffusion.

Compare Modern Brilliant cut to Old Mine.

Diamond gemstones are created by cutting precise facets, or tiny polished faces, in the stone. This is possible by cutting along the diamond’s natural points of cleavage, by grinding down its surfaces with another diamond, and by employing modern laser techniques.

There are 58 total facets on the round brilliant diamond. Thirty-three facets, including the table - the largest top facet - are cut above the girdle, the diamond’s widest circumference. Below the girdle – in an area called the pavilion -- are twenty-four more facets and the culet, or bottom point.

Brilliance is the term used to describe those astounding flashes of light you see when bright light hits a diamond. Brilliance is caused by white light reflecting off the diamond’s surfaces and the mirrored depths of the pavilion. Flashes of color within the stone are called fire or dispersion. Fire and brilliance give diamonds their beauty and increase their value.

The key to excellent fire and brilliance is proportion. Light striking a diamond that is cut too shallow will fall through the bottom rather than reflect as brilliance. Likewise, a diamond that is cut too deep will have less brilliance because light hitting the bottom cannot be bounced back to the top.

SHAPES

In the jewelry industry, the word "cut" usually brings to mind the shape or the outline of a diamond’s front. The seven most popular and fashionable shapes are the round brilliant, marquise, pear, emerald, oval, princess, and heart.

	Round Brilliant -- The modern classic for cut diamonds. 58 facets offer great brilliance and stability. This shape is most common and most popular for solitaire pieces.
	Marquise -- Currently a very popular shape for engagement rings. The brilliant style marquise, with its distinctive pointed oval form, carries the name of a French noblewoman. The pointed ends make this shape the most fragile and the most expensive of brilliant style cuts.
	Pear -- Less expensive than the marquise, but just as distinguished looking. Cut to maximize brilliance like the round brilliant, the pear shape has one pointed end -- and so, it has the same issue of fragility as the marquise.
	Oval -- If you are looking for a unique alternative to the round brilliant, the oval may be just what you want. It has excellent light dispersal like the round, but its shape may make it look larger than a round diamond of the same weight and quality.
	Emerald -- So named because it is the shape most associated with emerald gemstones, this is the most expensive shape for cut diamonds. Fewer facets distract the eye from any inclusions, so the emerald cut diamond generally has higher clarity. But, with fewer facets comes less brilliance than the other shapes. And, the emerald cut can look dull quickly, especially if you tend to wash your hands and put lotion on while wearing your jewelry.
	Princess -- Remarkably lovely and eye catching, this diamond shape is very popular right now, especially in "invisible" settings. Better yet, its sparkle won’t dull as quickly as the emerald cut.
	Heart -- A very special and romantic shape. The heart shape diamond is difficult to make perfectly proportioned, but it’s not hard to love. This shape is full of fire and brilliance like the round and the marquise.
	Baguette -- These small, rectangular diamonds are cut to maximize brilliance like the shapes described above. But, their major duty is to fill in channels, or stable grooved tracks, around a gemstone centerpiece. Jewelry designers sometimes only use baguettes to create dramatic contemporary looks for rings and pendants.

True Colors

Deep in the earth, when a diamond was being formed out of carbon, certain chemicals may have been drawn into the mix. The result is an added tinge of color in the transparent stone. Most common in diamonds is a degree of brown or yellow color, but diamonds have been found in all the colors of the rainbow.

When jewelers talk about the "fine color" of a diamond, what they really want you to notice is how little visible color the stone has. Colorless, or icy white, diamonds are the most prized and most expensive. The slightly colored diamonds are less valuable than the perfectly white or boldly colored red, yellow, and blue "fancies." The 45.52 carat Hope Diamond, on display at the Smithsonian, is remarkable in part for its prized cornflower blue color.

Diamonds are graded according to the GIA color chart.

Private companies once used their own grading systems and called diamond colors AA+, AB, 1+, etc. The GIA (Gemological Institute of America) - an independent, non-commercial association - wanted to create a standard chart that couldn’t be compared or confused with others. Thus, the perfectly colorless diamond is now given a color rating of D. Any company that tries to sell you a diamond they rate as "A+" in color is probably up to no good.

Crystal Clear?

Clarity is the term used to describe a diamond’s clearness or purity. Taken into consideration are the number, size, nature, and location of imperfections on the finished gemstone. Internal flaws are called inclusions, and external ones are called blemishes. Many of these are not visible to the naked eye, but under magnification, tiny featherlike shapes, crystals, bubbles, and dark flecks become apparent. These marks are as distinctive and recognizable as fingerprints -- in fact, they are commonly referred to as the diamond’s fingerprint. The more imperfections there are in a diamond and the more visible they are to the eye, the lower the market value.

Organic Carats

Diamonds are measured in terms of weight, not size. The heavier the diamond, the greater the carat weight. The name "carat" is derived from the carob seed. These seeds are remarkably consistent in weight and size and so were the favored scale balances in ancient markets. Carat weight should not be confused with "karat," the term used to describe gold’s fineness or purity.

A gem carat equals 200 milligrams, and there are 142 carats to every ounce. A carat is composed of one hundred points. Jewelers evaluate a diamond’s carat weight by using an exceptionally sensitive metric scale that measures weight in points. So, a 1/4 carat diamond is also called a 25 point diamond. Because large diamonds are extremely rare -- and diamonds over one carat in size are becoming increasingly so -- every tiny increase in weight can result in a big increase in market value. Generally speaking, the larger the diamond, the higher the price. Even a large diamond that has so-so color and clarity will cost more than a smaller but finer diamond, simply because the larger ones are scarce.