The GIA 4C's grading system

Because diamonds are so valuable, it’s essential to have a universal grading system for comparing their quality. In the 1940s and ’50s, GIA developed the 4Cs and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds.

The Four Cs of diamond quality will give you a multitude of information about a diamond’s characteristics and value, but they can’t begin to describe one elusive quality – beauty. To do that, you’ll need to experience the diamond with your own eyes.

Carat Weight

Carat weight is the most intuitive of the 4Cs – you expect a larger diamond to be worth more when assigning diamond values.

Diamonds and other gemstones are weighed using metric carats with one carat weighing about the same as a small paper clip, or 0.2 grams. Just as a dollar is divided into 100 pennies, a carat is divided into 100 points which means that a diamond of 50 points weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other three characteristics of a diamond’s 4Cs: clarity, color, and cut.

Because even a fraction of a carat can represent a considerable difference in cost when purchasing diamonds, exact precision is crucial. In the diamond industry, weight is measured to a thousandth of a carat and rounded to the nearest hundredth. Each hundredth is called a point (a 0.25 ct. diamond would be called a “twenty-five pointer”). Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)

What are "magic sizes"?
Some weights are considered "magic sizes" - half carat, three-quarter carat, and carat. Visually, there's little difference between a 0.99ct. diamond and one that weighs a full carat. But the price differences between the two can be significant.

Color

The Color of the diamond is all about what you can't see.

Diamonds are valued by how closely they approach colorlessness – the less color, the higher the value. Most diamonds found in jewelry stores run from colorless to near-colorless with slight hints of yellow or brown. The only exceptions are the fancy-color diamonds that lie outside of this range.

GIA's diamond color-grading scale is the industry’s most widely accepted grading system. The scale begins with the letter D, representing colorless, and continues, with increasing presence of color, to the letter Z. 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 that they are invisible to the untrained eye. But these slight color differences make a very big difference in diamond quality and price.

Clarity


Diamond Clarity refers to the absence of internal inclusions or external blemishes.

Because they are created deep within the earth, most diamonds contain unique birthmarks called inclusions (internal) and blemishes (external). Diamonds with very few birthmarks are rare and, of course, rarity affects a diamond’s value. Using the International Diamond Grading System™, created by GIA, diamonds are given a clarity grade that ranges from flawless (FL) to diamonds with more prominent inclusions (I3).

Every diamond is unique. But none are absolutely perfect even though some come close, even under 10x magnification. Known as flawless diamonds, they are exceptionally rare.

The GIA Clarity Scale contains 11 grades, with most readily available diamonds falling into the VS or SI categories. In determining a clarity grade, GIA considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10x magnification.

• Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
• Internally Flawless (IF) - No inclusions and only minor 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
• Imperfect (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance

What causes inclusions?
Small crystals can become trapped in a diamond when it’s forming. Sometimes as a crystal grows it can develop irregularities in its atomic structure.

Cut

Cut fuels the diamond’s fire, sparkle, and brilliance.

It seems miraculous that the traditional 58 tiny facets in a diamond, each precisely cut and sharply defined, may be only two millimeters in diameter. But without this precision, a diamond wouldn’t be near as beautiful as it is. Without a doubt, the allure of a particular diamond depends more on cut than anything else.

Though extremely difficult to analyze, the cut of a diamond has three attributes: brightness (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the light flashes – or sparkle – when a diamond moves).

An understanding of diamond cut begins with the shape of a diamond, with the standard round brilliant dominating the majority of diamond jewelry. All other diamond shapes are known as fancy shapes or fancy cuts and include the marquise, pear, oval, and emerald cuts. Hearts, cushions, triangles, and a variety of other new shapes are also gaining popularity in many forms of diamond jewelry.

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.

In early 2005, GIA unveiled a diamond cut grading system for standard round brilliants in the D-to-Z color range. This system, the product of more than 15 years of intensive research and testing, assigns an overall diamond cut grade ranging from Excellent to Poor.