Diamonds - The Four C's

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Learn what to look for. Decide your priorities. Then make the choice that's right for you.


When selecting a diamond, one of the "Diamond 4 Cs" refers to Carat Weight. Diamonds are sold by the carat (ct), which is a unit of weight, not size.

The word "carat" is derived from the Arab word for carob, as carob seeds were used in early trading days to determine the weight of diamonds. While this method may seem unscientific, the carob seeds were so uniform in size and weight that they produced highly reliable measurements. Today, we use very sensitive, accurate scales to measure the weight of a diamond.

One carat weighs 200 milligrams, or one-fifth (.2) of a gram. This standard has been in use worldwide since 1914, when it was proposed by the International Committee on Weights and Measures. Note that the term "carat" – which is a measurement for precious gems – is different from the term "karat," which refers to gold quality in the United States.

A few pointers

When discussing gemstones of less than one carat, jewelers often refer to the weight in terms of points. A carat is divided into 100 points, with one point corresponding to .01 carat. Think in terms of pennies to a dollar. There are one hundred pennies in a dollar, and there are one hundred points in a carat. So a 1/2 carat gemstone equates to 50 points, a 1/4 carat diamond 25 points. Very small gemstones, such as those used in pavé or channel settings, are sometimes called melee. Melees range from .01 to .16 carat in weight.

When isn't a carat 100 points?

Although the analogy of pennies to the dollar suggests that one carat is always 100 points, or that one-half carat is always 50 points, that's not entirely true. Diamonds can't all be uniformly cut to such exact weights, so the carat weight given is an approximation of the actual weight of the gemstone.

The impact of weight on price

Since diamonds become rarer as they increase in weight, the larger the diamond, the more valuable (and costly) it is. But the price of a diamond does not increase at the same rate as its weight. The larger the gemstone (all else being equal), the more disproportionate the increase in cost per carat. For example, a 2-carat diamond is always more expensive than two 1-carat diamonds of the same quality.

When evaluating diamonds, weight and size are not the same thing. Yet, carat weight has come to represent particular sizes when based on a well-cut diamond. Although your computer's monitor may affect the accuracy, the following chart will give you a good idea of approximate diamond size by carat weight and diameter in millimeters for one of Shane's well-proportioned brilliant-cut gemstones.

What should you look for?

Since ancient times, diamond cutters have sought to produce a diamond of maximum possible weight and quality from the rough crystal. Similarly, while your first inclination may be "bigger is better," that's not necessarily true for everyone, as quality and budget need to be considered.



The "C" of clarity refers to a gemstone's purity. Clarity is evaluated by viewing the gemstone under 10X magnification. Virtually all diamonds contain tiny natural birthmarks that are present to varying degrees. After all, nature is rarely perfect, and that extends to diamonds! These marks serve as the identifying "fingerprint" that makes every gemstone unique.

What is that speck?

These tiny identifying marks consist of "naturals" on the outside or inclusions on the inside of the gemstone. Inclusions refer to anything that is trapped within the diamond crystal. Nearly all diamonds, even those of the highest quality, have some inclusions, which fall into these categories:

Mineral inclusions
A dark spot from a trapped bit of mineral
Open cavities interrupting the diamond surface that were a part of the original diamond crystal
Internal cracks or fractures caused by either internal or external stress during the diamond's formation.

How clarity is graded

While there are several grading systems used in the industry, the most recognized and commonly used system is the one developed by the Gemological Institute of America (GIA).

Flawless. Shows no inclusions or blemishes of any sort under 10X magnification when examined by an experienced grader. Extremely rare.
Internally Flawless. Has no inclusions when examined by an experienced grader using 10X magnification. Very rare.
Very, Very Slightly Included. Contains minute inclusions that are difficult even for experienced graders to see under 10X magnification.
VS1, VS2
Very Slightly Included. Contains minor inclusions ranging from difficult to somewhat easy to see for an experienced grader when examined under 10X magnification.
SI1, SI2
Slightly Included. Contains inclusions that are easy to very easy to see for an experienced grader under 10X magnification. Some inclusions may be visible to the unaided eye.
Included. Contains obvious inclusions visible to an experienced grader under 10X magnification; can be visible without magnification.
I2, I3
Included. Contains obvious inclusions. Visible without magnification.

The effect of positioning

As a rule, the less visible the location of the inclusion, the less impact on the gemstone's value.



Of the 4 Cs criteria, the quality of color refers to a diamond's body color, not the rainbow surface of reflected light.

Why less color is more valuable

When buying a diamond, it is the absence of color that makes one diamond more precious than another. The whiter or more colorless the gemstone, the more rare, and the higher the price. The exception is "fancy" colored diamonds, which can occur in shades of blue, pink, red, yellow, green and brown. Some of these are exceptionally rare and considered collector's items.

Most diamonds that are mined have a great deal of body color while very few are completely absent of color. For a mental picture of "colorless" or the "absence of color," just think of pure water.

Making the grade

Color is graded by the Gemological Institute of America (GIA) with letters ranging from D (completely colorless) to Z (light yellow).

GIA Color Rankings
D, E, F
G, H, I, J
Near Colorless
K, L, M
Faint Yellow
N, O, P, Q, R
Very Light Yellow
S, T, U, V, W, X, Y, Z
Light Yellow

More than meets the eye

Color is actually one of the most difficult factors to evaluate. For one thing, everyone sees color differently. Differences in color between gemstones are very, very subtle, and may be imperceptible to an untrained eye. In fact, even the experts will compare an ungraded gemstone to one previously graded to properly assess its color. Small differences in color can make large differences in the price.

Color and the Setting

A diamond may exhibit the color of its setting, which is why most ring settings will have a white gold or platinum head. White gold and platinum have the least effect on the diamond's color. Conversely, a diamond with more body color is often best enhanced by a yellow gold setting. Of course, the setting you choose is a matter of personal preference.

Facts about fluorescence

Some diamonds naturally exhibit a bluish tint when viewed in daylight or under fluorescent lighting. Under candlelight or normal incandescent lights, the blue disappears. This blue tint is the result of the gemstone's degree of fluorescence. It is not considered either good or bad, but simply an inherent characteristic of the gemstone.



The cut is extraordinarily important because it has the greatest single influence on the diamond's brilliance, or sparkle. And when it comes to diamonds, sparkle is what makes diamonds "a girl's best friend."

Occasionally you may find other jewelers' gemstones are priced lower than Shane Co. diamonds of identical carat weight, color and clarity. That's because the diamonds at the other jewelers are cut too shallow or too deep – causing the light that enters them from above to leak out of the bottom and sides of the gemstone. As a result, these gemstones are visibly dull and dark and consequently, highly undesirable. Remember: it takes all 4 Cs to complete the picture and determine a diamond's value.

So pay special attention to cut when evaluating diamonds and believe your eyes.

Shane Co. handpicks only diamonds with the most sparkle.

Judging a diamond’s sparkle by its lab grade alone is like judging a movie solely by its rating. A laboratory grade is only part of the story, because diamonds with the same grade can have very different amounts of sparkle, depending on how each diamond is cut and where the inclusions are located inside the diamond. When Shane Co. buys diamonds, our own buyers go directly to the diamond cutters around the world and examine groups of diamonds already sorted by grade. Then they handpick only the diamonds with the most sparkle from within each grade. Whatever diamond grade you choose, you will clearly see the difference in the way Shane Co. diamonds sparkle.

The part of the diamond above the girdle
The large facet that caps the crown of a gemstone
The outer edge of the diamond, usually the portion that is grasped by the setting. It is the dividing line between the crown and the pavilion.
The part of the diamond below the girdle.
The small facet parallel to the girdle, at the bottom of the gemstone.

An exacting talent

Of the four qualities that define a diamond's value, the cut is the only one determined by a human being. A skilled diamond cutter realizes the rough diamond's potential. He cuts and facets the crystal to reflect the maximum amount of light inside the gemstone and back through the top of the diamond. His objective is to produce a perfectly symmetrical gemstone whose right and left sides are mirror images of each other.

At the same time, he has to find the optimal balance between yielding the most diamond weight and creating the best proportioned cut. One reason why higher grades of cut are so much more costly is because more diamond was sacrificed to create them. That's also why a well proportioned one-carat diamond may be worth twice as much as a poorly proportioned larger diamond that lacks fire and brilliance.

In search of the "ideal"

For centuries, diamond cutting experts have pondered what combination of proportions creates the optimal balance of brilliance, scintillation and dispersion (the diamond's sparkle and fire).

The 58-facet model developed in 1919 by master gem cutter and mathematician Marcel Tolkowsky has provided a foundation for today's most widely accepted proportions. However, while Tolkowsky's model dictated precise proportions for table diameter, crown height, pavilion depth, crown angle and pavilion angle, many grading labs and diamond sellers today offer a more liberal interpretation. The market itself dictates a wider range of acceptable proportions.

In fact, the Gemological Institute of America (GIA), the world's leading gemological authority, actually advises against using the term "ideal" cut. Why? Because the GIA has demonstrated that literally thousands of variations on these proportions can maximize the different optical characteristics displayed by a diamond. As long as the diamond's proportions fall within the acceptable range of tolerances (and Shane Co. searches the world's markets for the finest cuts), you can be assured of buying a gemstone that is well made. Furthermore, you could view two gemstones with vastly different cut proportions, and be hard-pressed to determine which gemstone is more beautiful.

For appearance's sake

The way a gemstone is cut can affect its appearance in other ways. If the diamond has a deep cut, it actually looks smaller than another diamond of the same weight that is cut well. Likewise, a diamond that has a spread cut (cut shallow) will appear larger than another diamond of the same weight that is cut well. A diamond that is cut either too deep or too spread is typically undesirable.