The Four C's of Diamonds

In the 1940s and '50s, GIA developed the 4Cs and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds.

The Four C's describe the fundamental characteristics of diamonds. The Four C's stand for:

• Carat
• Color
• Clarity
• Cut

Carat

Diamonds and other gemstones are weighed in metric carats. So what's a carat weigh-in at? About the same weight as a paperclip. (Don't confuse carat with karat, as in "18K gold," which refers to gold purity.) Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. The carat is only one of the defining aspects of a diamond's value.

The carat, the standard unit of weight for diamonds and other gemstones, takes its name from the carob seed. Gem traders once used them as counterweights in their balance scales. The modern metric carat, equal to 0.2 grams, was adopted by the United States in 1913 and other countries soon after. Today, a carat weighs exactly the same in every corner of the world.

Color

The absence of the second C, diamond color is another factor which determines diamond value. Diamonds are valued by how closely they approach colorlessness – the less color, the higher their value. (Pink and Blue Diamonds, the fancy color diamonds, are not held to this.) Most diamonds found in jewelry stores run from colorless to near-colorless, with slight hints of yellow or brown.

The industry standard for color-grading was developed by the GIA. The scale begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or near-colorless. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

Many of these color distinctions are so subtle as to be invisible to the untrained eye. But these slight differences make a very big difference in diamond quality and price. Why does the GIA color grading system start at D?

Clarity

Diamond clarity refers to the absence of inclusions and blemishes. Diamonds without these birthmarks are rare, and rarity affects a diamond's value. Using the GIA International Diamond Grading System™, diamonds are assigned a clarity grade that ranges from flawless (FL) to diamonds with obvious inclusions (I3).

Every diamond is unique. None is absolutely perfect under 10× magnification, though some come close. Known as Flawless diamonds, these are exceptionally rare. Most jewelers have never even seen one.

Here are the definitions of various clarity levels, as defined by the GIA

• Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
• Internally Flawless (IF) - No inclusions and only blemishes are visible to a skilled grader using 10× magnification
• Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
• Very Slightly Included (VS1 and VS2) - Inclusions are clearly visible under 10× magnification but can be characterized as minor
• Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader using 10× magnification
• Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance

Cut

The fourth C, Cut is the factor that fuels a diamond's fire, sparkle and brilliance.

The traditional 58 facets in a round brilliant diamond, each precisely cut and defined, are as small as two millimeters in diameter. But without this precision, a diamond wouldn't be nearly as beautiful. The allure of a particular diamond depends more on cut than anything else. Though extremely difficult to analyze or quantify, the cut of any diamond has three attributes: brilliance (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the flashes of light, or sparkle, when a diamond is moved).

As a value factor, though, cut refers to a diamond's proportions, symmetry and polish. For example, look at a side view of the standard round brilliant. The major components, from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion that's known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth. A wide range of proportion combinations are possible, and these ultimately affect the stone's interaction with light.