4Cs of Diamond Quality

We are often asked why the best color for a diamond is a D and not an A? And why are diamonds measured in carats instead of grams or ounces? What is a carat, anyway? This article explains in detail what you’ll find on a diamond certificate.


The first C, Contrary to popular belief, the diamond color grading scale begins with “D” not because we expect to someday discover an even better color that would be graded A, B, or C, but to avoid confusion.

Prior to the mid-20th century, jewelers and diamantaires had no uniform language or standard to describe a diamond, so they used a variety of systems, and the interpretations of those descriptions were pretty loose as well. One jeweler’s “A” color was another jeweler’s “1” while another called it “blue-white,” and so forth. Clearly this made it hard for consumers to know what they were buying.

The Gemological Institute of America (GIA) created the first globally accepted standard and a universal language for describing and grading diamonds: the Four C’s of today. -GIA picked D to represent the best color as a way to start fresh and avoid any association with prior terminology. The GIA diamond color scale runs from D—colorless—through Z, where a slight color is visible to the naked eye.
With each successive grade, a diamond’s value decreases ever so slightly, though it takes a jump of several grades before the difference is obvious.
Stones that have more color than Z start to increase in value again as the color grows more saturated. These are considered fancy color diamonds and they have their own separate evaluation system.

clarity scale

The second C, Just as diamond color terminology was inconsistent before GIA’s grading scale, so were descriptions of clarity. Since natural diamonds are formed from carbon subjected to tremendous heat and pressure deep within the earth – small traces of crystals or other minerals are sometimes trapped within the carbon atoms as the diamond is being formed. Inside the diamond, these characteristics are called inclusions; external characteristics are called blemishes.

The fewer of either, the more rare and valuable the diamond is.

Old clarity terms like “loupe clean” do not mean much unless one knows the strength of the loupe being used. As a result, GIA developed a clarity scale based on 10x magnification and it has 11 grades: Flawless, Internally Flawless, Very Very Slightly Included (VVS1 and VVS2), Very Slightly Included (VS1 and VS2), Slightly Included (SI1 and SI2), and Included (I1, I2, and I3). Stones with an “I” grade have enough inclusions to impact their transparency and brilliance.

All about cut

Many people commonly confuse the third C, “cut” with shape. Names like round, pear, marquise, and so forth refer to the diamond’s shape, but cut refers to the arrangement of facets to maximize a diamond’s brilliance. This is where the skill of the diamond cutter can make or break the value of a stone.
Prior to the early 20th century, diamonds were cut with different facet angles than they are cut with today, resulting in a soft glow rather than a brilliant sparkle. The 58-facet arrangements and proportions of today’s round brilliant cut was invented in 1919 by a Polish/Belgian mathematician named Marcel Tolkowsky. The proportions he devised became known as the “Ideal” cut and became the benchmark for the industry. However, the skill of the cutter in achieving those proportions plays a major role in the finish of the stone. Tolkowsky’s formula remained unchallenged until the mid-2000s, when GIA and the American Gem Society (AGS) as well as others began to experiment with different proportions to see if any would create even greater brilliance. Cutters continue to experiment with different proportions today, but Tolkowsky’s formula consistently produces an excellent finish. It only applies to round stones, though; other shapes require different facet arrangements and have different expectations of light return (brilliance)
The cut experiments of the mid-aughts also produced two diamond cut grading scales: GIA’s, which has five grades: excellent, very good, good, fair, and poor; and AGS’s, which goes from zero (best) to 10 (worst). Both GIA and AGS grades take into account face up appearance, design, craftsmanship, light performance, proportion, and finish. Another laboratory, AGA, also has a cut grading scale with excellent to poor rating terminology like GIA.

What is a carat?

The forth C on your grading certificate is carat weight. The origin of the carat as a unit of measurement for gemstones dates back to the ancient world, where Mediterranean traders needed a reasonably uniform unit of measurement for goods. Both the carob seed and the wheat grain were fairly consistent from one to the next, and thus became standards of measurement. The carob seed in particular became the standard of measurement for gemstones, and the Arabic word for carob through centuries of translations eventually became today’s carat.
The metric equivalent of one carat is .2 grams (thus, 5 carats = 1 gram). This standard was adopted worldwide in the early 1900s and remains in use today.
GIA’s grading system is the industry’s most widely accepted standard, and other gemological laboratories use it as well. The rigor with which the standards are applied can vary, however, which is why reports from certain gem labs are preferred over others for high-value stones. GIA is globally accepted as a benchmark, but reports from HRD (Hoge Raad voor Diamant) in Antwerp, Belgium and the AGS (American Gem Society) Laboratory in the United States are also often used but it is our preference to only use GIA cuts.