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Diamond quality is assessed based on the 4Cs: Cut, Color, Clarity, and Carat Weight. This standard, developed by the Gemological Institute of America (GIA), has become the universal method for judging diamonds. At Jules, we explain the 4Cs to our diamond shoppers and demonstrate the differences between apparently similar stones, encouraging comparison among a number of diamonds that fall within each customer’s budget.
The cut of a diamond refers to the proportion and arrangement of its facets and the quality of workmanship. These things affect how well a diamond interacts with light, thereby determining the amount of its brilliance, sparkle, and fire. As such, cut is a diamond’s most important characteristic, having the greatest overall influence on its beauty.
In grading cut, gemologists consider the proportions of the diamond’s facets: The table is the top of the stone. The crown is the top portion, extending from the table to the girdle. The girdle is the intersection of the crown and the pavilion, which defines the perimeter of the diamond. The pavilion is the bottom portion, extending from the girdle to the culet. The culet is the facet at the bottom tip of the stone. When a diamond is cut with the proper proportions, light is returned out of the top, maximizing the stone’s brilliance. A pavilion depth that is too shallow or too deep allows light to escape from the side or bottom of the stone.
The cut grade also takes into account the craftsmanship of the diamond, including the symmetry of its facet arrangement and the quality of polish on those facets. The GIA recognizes five cut grades: Excellent, Very Good, Good, Fair, and Poor.
(Note: The cut of a diamond does not refer to its shape, which is discussed later.)
Color is generally considered to be the second most important characteristic of a diamond, because it is visible to the naked eye. Diamond color evaluation is actually based on the absence of color, since the less color in the stone, the more desirable and valuable it is. The GIA’s color scale ranges from D to Z and is the industry’s most widely accepted grading system. Stones that are D-F are considered Colorless; G-J are Near Colorless; K-M are Faint Yellow; N-R are Very Light Yellow; and S-Z are Light Yellow. The GIA scale starts at letter D to avoid any association with earlier systems based on A, B, and C grades.
Fluorescence, which is related to color, is caused by a trace amount of the element boron in the diamond. It is activated by UV light. Fluorescence in a diamond is described as: None, Faint, Medium, Medium Blue, Strong, Strong Blue, and Intense Blue. While diamonds with no fluorescence are considered purer and, therefore, more valuable, the presence of fluorescence may give diamonds that have color a whiter appearance.
(Note: Naturally colored diamonds outside the normal color range are called fancy color diamonds and are very rare. Zs are not considered a fancy color.)
Clarity measures the amount, size, and placement of imperfections in a diamond. Natural diamonds are the result of carbon exposed to tremendous heat and pressure deep in the earth. This process can result in a variety of internal characteristics called ‘inclusions’ and external characteristics called ‘blemishes.’ The evaluation of diamond clarity involves determining the number, size, relief, nature, and position of these characteristics, as well as how they affect the overall appearance of the stone.
The GIA diamond clarity scale has six categories, some of which are divided, for a total of 11 specific grades: Flawless (FL) diamonds have no inclusions and no blemishes visible under 10X magnification. These are extremely rare. Internally Flawless (IF) diamonds have no inclusions visible under 10X magnification. These are very rare. Very, Very Slightly Included (VVS1 and VVS2) diamonds have inclusions that are so slight, they are difficult for a skilled grader to see under 10X magnification. Very Slightly Included (VS1 and VS2) diamonds have inclusions that are observed with effort under 10X magnification, but can be characterized as minor. Slightly Included (SI1 and SI2) diamonds have inclusions that are noticeable under 10X magnification, but not to the unaided eye. Included (I1, I2, and I3) diamonds have inclusions that are obvious under 10X magnification and may be noticeable to the unaided eye. While the majority of diamonds that are mined have inclusions that are visible to the unaided eye, those graded SI2 or better are generally considered ‘gem quality.’
Carat refers to a diamond’s weight. While people often think of ‘carat’ as a description of size, several diamonds with equal weight can have different measurements (usually expressed in millimeters), because the stones are cut with different proportions. A metric carat is defined as 200 milligrams. Each carat can be subdivided into 100 ‘points,’ so that 25 points equals ¼ carat, 50 points equals ½ carat, etc. Two diamonds of equal carat weight can have very different quality and price when the other three Cs are considered. Price per carat increases at the full- and half-carat weights. Therefore, if all other factors are equal, a 2 carat diamond will cost more than twice as much as a 1 carat diamond.
Shape describes a diamond’s form, primarily as viewed from above. The beauty of the individual shapes is a matter of personal taste. Popular shapes are: Round, Princess, Emerald, Asscher, Radiant, Cushion, Marquise, Oval, Pear, and Heart.