The 4C's of Diamond Buying

The most commonly used concepts in grading diamonds are Cut, Clarity, Carat, and Color. Each one of these is addressed in more detail below.  NOTE: The so-called 4C's of diamonds are not enough to completely value a diamond, and the information provided here is for reference only. We recommend you consult a jewelry professional before purchasing high end diamonds.

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Color - All diamonds are graded on a color scale ranging from D to Z, with D being colorless, and Z being very yellow. For example, see the color scale and table below. The most common diamond colors are G and H. (Note. due to limitations of computers, these colors are only approximate)

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Clarity - Diamonds are also judged by the size and amount of inclusions (defects) in the stone. Geologically, an inclusion is "a solid fragment, liquid globule, or pocket of gas enclosed in a mineral or rock." In gemmology, this definition is usually extended to include any other feature of the gemstone which impedes the free passage of light through the stone. This includes changes in crystal growth direction (e.g. twinning), and external features, such as fissures which run from the surface into the stone, naats , trigons, and zones of color absorption (e.g. the very common color banding seen in sapphire). Not all inclusions are visible either with the naked eye, or under the standard 10 times magnification used by gemmologists. Many consumers believe that inclusions are things which are visible to the naked eye, and that if no inclusions can be seen, then the stone is perfect. Some stones contain many areas of "twinning", where the growth direction of the crystal has changed during its formation, and these areas can absorb or refract light in such a manner as to reduce the brilliance of the stone. Other stones contain large numbers of small inclusions, some visible under 10x magnification, others not, because they are too small. These clouds of microscopic inclusions can reduce the passage of light through a stone so severely that the stone looks "dead", with no brilliance or fire whatsoever. Such stones usually have a slightly cloudy look to the naked eye. In recent decades, the GIA, Gemmological Institute of America, has influenced other gemstone grading bodies, such as CIBJO, throughout the world, and most countries now use the same standards as the GIA for diamond clarity, so that the GIA scale has become virtually an international standard. There still remain vast differences between commercial grading and laboratory grading. The European Gemlogical Laboratory is also recognized as a worldwide standard.

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Carat - Diamonds are weighed and cataloged according to their carat weight, often abbreviated as CTW. (one Carat = 0.20 Grams). Sometimes a diamond is also weighed on a point scale (100 points = 1 Carat). And as if that did not add enough confusion, sometimes the unit of Grain is used (1 Grain = 25 Points). Be sure to not confuse the use of Points as a unit of weight versus Points used to describe the diamond cut as described below. The size of the diamond is related to the carat weight, but it does not scale exactly, meaning that a 2CTW diamond is not twice the size of a 1CTW diamond.  The table below gives the approximate diameter of a perfectly proportioned brilliant cut diamond and the approximate carat weight.

It is possible to estimate the carat weight from measured dimensions of other cuts as well, but the accuracy is diminished. The carat weight of a diamond can only be measured precisely by weighing it, however this is very difficult to do once the stone has been placed in a setting. Unless you are obtaining jewelry direct from the manufacturer, all carat weight values are approximate, and deviation of the estimated value from the actual weighed value by +/- 5% is considered acceptable.

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Cut - Diamonds come in many different shapes, or cuts, some of which are indicated below. The choice of cut is a personal preference, with the round brilliant cut being by far the most popular.

The cut of a diamond is one of the things that influences the brilliance (or fire) of the stone. More important is that the stone is properly cut so as to reflect light back out of the diamond. Improperly cut stones can significantly reduce the brilliance or fire of the stone.

The amount of reflected light is controlled by the table depth, which is the measurement from the top of the stone to the tip. Proportions determine a diamond's brilliance (amount of light reflected back to your eye), fire (the flashes of color due to prismatic separation into the colors of the rainbow) and scintillation (sparkling movement of light as you move the diamond). Below are the approximate proportions to create a round diamond of maximum beauty, achieving an excellent balance between brilliance, fire and scintillation. (NOTE: These proportions only apply to round diamonds)

How do I know my Diamond is Genuine? - Diamonds are one of the most valuable gemstones, and there have been many attempts to either synthesize diamonds, or to pass other stones as diamonds. The most widely known among these is Cubic Zirconia, which can be very difficult to discern. The best way to determine the difference in a CZ and diamond is to measure the coefficient of thermal capacity. There are specialized instruments available that can readily discriminate between a CZ and a genuine diamond. A new material making its presence on the fake diamond market is Mozanite, which can spoof most low end diamond testers. Careful examination of Mozanite will show a wavy or stacked look to the stone. Recently, testers have come available to identify Mozanite. If you are ever in doubt, ask the person selling you the diamond to test it in front of you. If they do not want to - RUN. All reputable jewelers will be happy to show you that the diamond is real.

Another way to assure yourself that a diamond is genuine is to only purchase certified diamonds. Diamond certifications is done by several agencies, including the American  Gemological Association (AGA) and the European Gemological Laboratory (EGL). The diamond is inscribed with a unique number, typically along the girdle if the stone, and you should receive a paper certificate which contains a complete description of the diamond. Certified stones will typically cost a few hundred dollars more than uncertified stones. Certification of the stone is definitely a good option for high end diamonds.