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 4C’s, (Carat Weight, Color, Clarity and Cut) and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds.
A carat is divided into 100 points, but two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. 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.”)
Diamond color is all about what you can’t see. Diamonds are valued by how closely they approach colorlessness – the less color, the higher their value. (The exception to this is fancy-color diamonds, such as pinks and blues, which lie outside this color range.)
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.
Because diamonds formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes). Diamond clarity refers to the absence of these 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).
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).
An understanding of diamond cut begins with the shape of a diamond. The standard round brilliant is the shape most commonly used. All others are known as fancy shapes. Traditional fancy shapes include the marquise, pear, oval, emerald cuts, hearts, cushions, triangles and a variety of others are also gaining popularity in diamond jewelry.
As a value factor, though, cut refers to a diamond’s proportions, symmetry and polish.The major components, from top to bottom, are the crown, girdle and pavilion. A roundbrilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottomof 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 angleand pavilion depth. A wide range of proportion combinations are possible, and theseultimately affect the stone’s interaction with light. Measurements that are either tooshallow or too deep will inevitably let light escape through the sides or the bottom of thestone. A well-cut diamond will direct more light through the crown.