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. The majority of diamonds used in fine jewelry weigh one carat or less.
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.”)
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.
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. Most jewelers have never even see one.
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
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, the girdle, and the pavilion. A round brilliant cut diamond can have either 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion, 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 synchronicity 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.