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The 4 C's and Comparison Shopping


TIP: Although cut can be difficult to grade, it is a very important comparison factor, affecting price by up to 50%.

First, this does not refer to the shape diamonds are cut into (e.g., round, oval, arquise, pear, heart, emerald). As a grading factor, cut refers to the manner in which the diamond was fashioned by the cutter. In order to maximize the sparkle that is so highly valued in a diamond, each of the facets, which act as mirrors, must be in proper geometric relationship to one another. The better the cut, the better the diamond's ability to handle light and provide brilliance and/or fire.

The ethics of diamond cutting
Relatively few diamonds are properly cut. Diamond cutters get paid for weight retention, not to make the most beautiful or durable diamonds. Beauty is sacrificed to save stone weight because that is how the typical consumer has been led to value a diamond  ~ the bigger the better ~ when in actual fact they may be paying for padding of a cut that does not maximize sparkle.

Even those informed of the 4 C's may be tempted to brush off the cut factor, especially since it is a complex assessment with no standardized grading system. Some jewelers count on this, and intentionally stock poorly cut stones with good color and clarity grades. They pay less for the poorly cut stones, and so can charge less, thus the shopper obtaining quotes by phone may think they've found the best deal. This is fine if the consumer understands that the saving was achieved by sacrificing cut. Too often that is not the case.

TIP: Because of the lack of a recognized grading system, cut as a grading factor can be more easily distorted or abused. Protect yourself with the information from this website.

Remember that you haven't truly compared "apples to apples" until you have also evaluated the cut of the diamonds you are comparing. There's a reason for that 50% price difference between a well-cut and poorly-cut diamond. Once you've experienced the sparkle of a well-cut diamond, don't be surprised if you decide to drop a grade in color or clarity, or buy a smaller stone, in favor of a better cut.

As you learn to identify a well-cut (or "well-made") diamond, it will help if you review the diagrams below and become familiar with the structure and vocabulary of the most popular shape and cut today, the round brilliant.

In addition to carat weight, useful measurements are
(in millimeters)

Table Size = Diameter of the flat top facet, corner to corner
Total Depth = Measure of stone viewed from side, table to culet
Width = Diameter of stone at its widest point, the girdle

In a well-cut diamond, light coming into the top will bounce around and come back through the top or "crown" (Fig.#1). If a diamond is cut too deep, light will escape through the side (Fig. #2.). If it is cut too shallow, light will escape through the pavilion or bottom (Fig. #3). Viewed in profile, from the side, seek a rough proportion of 1/3 above the girdle and 2/3 below. For shapes other than round, the most common evaluator of cut is the ratio of stone width to length.

Many experts consider cut to be the most critical of the diamond's 4 C's. Yet there is no established grading system for cut, no standard cut endorsed by the entire industry. That is because cut is not a natural property (like color and clarity), but a product of human choices, reflecting diverse opinions as to what constitutes beauty in a diamond, how to achieve it, and how to do so cost-effectively and enhance value. Standards and practices in diamond cutting are a matter of evolution, affected by market forces (supply, demand, and current cultural norms of beauty), and technological and scientific advances (cutting equipment, and discoveries in the field of optics). The evolution of diamond cutting continues even today, leaving the phrase "ideal cut" open to discussion.

Despite the lack of a true grading system for cut, there are well-accepted working definitions and measures available to assess this most important property of a diamond. For round diamonds, the GIA uses a series of measurements and assigns one of four classifications (not "grades"):

  • Class 1 - Virtually "ideal" proportions and finish. Rare, therefore more expensive then a Class 2 cut, all other factors being equal.
  • Class 2 - Internationally perceived as well cut. The standard for most wholesale price guides and for fine jewelry.
  • Class 3 - An unexceptional cut, with no major defects. May represent a slight defect in handling light to save weight.
  • Class 4 - Cut and finish defects resulting in unattractive optical side effects, many visible to the layperson and the unaided eye.

Basic Tests for Cut

Because so few stones carry these classifications, it is important that the informed consumer be able to conduct some basic assessment of their own. The experts employ many sophisticated measures to analyze cut (which we won't go into here), but they also rely heavily on some simple calculations, using measurements that should be available from any credible jeweler: the weight, width and total height of the diamond.

Width per Weight -- On the following chart, look up the weight of the stone being evaluated, and compare its width to the charted width for that weight. If off by more than 1/10th mm, plus or minus, expect or request a discount. This test also addresses the issue of  "apparent size" from the face or top. A wide/shallow diamond "faces-up" larger than a narrow/deep diamond, looking heavier than it is. As long as a diamond still meets other cut criteria, to face up large can add to its value. But remember, if a stone is disproportionately wide, it hurts sparkle, and a stone that is too wide/shallow, allows imperfections to be more easily seen within the stone. So "apparent size" is not the only issue.

TIP: To assess cut of a round diamond, if you do nothing else, at least:
    Find weight on chart below. COMPARE YOUR STONE'S WIDTH WITH THE CHARTED WIDTH. Be wary (seek discount) if more than .1mm off.


The American Ideal is roughly 60% for each. Reject the stone if below 50 or above 70, and read further if near those limits.

Round Diamonds  *  Desirable Width per Weight
(plus or minus .1mm)
.25 CT = 4.1mm
.33 CT = 4.4mm
.50 CT = 5.2mm
.65 CT = 5.5mm
.75 CT = 5.8mm
.85 CT = 6.2mm
1.00 CT = 6.5mm
1.25 CT = 7.0mm
1.50 CT = 7.4mm
1.75 CT = 7.8mm
2.00 CT = 8.2mm
2.25 CT = 8.6mm
2.50 CT = 8.8mm
3.00 CT = 9.4mm
4.00 CT = 10.2mm
For weights not on the chart, contact Wooden Skate Jewelry & Gems for the desirable diameter of your exact stone.

Total Depth Percentage -- This is the second simple test of a diamond's proportions. Divide the stone's total height (from table to culet) by its width (diameter at girdle) and compare to this chart:

56-63% =
60% =
63-65% =
Under 56% =
Over 65% =
Borderline ~ discount slightly
Too Shallow ~ discount substantially
Too deep, poor apparent size ~ discount severely

Table Percentage -- Divide the diameter of the table by the diameter at the girdle, and compare the result to this chart:

51-69% =
51-55% =
59-62% =
60-69% =
50 or below/

70 or above =

Cuts favoring fire (Tolkowski Brilliant, European cuts)

Trading off fire for brilliance
Undesirable ~ discount severely

TIP: Examine a number of different diamonds, learning to recognize sparkle, fire, and brilliance, and determine your preference. Don't become so focused on the technicalities of cut that you miss the sensory message as to what pleases your eye.

Fire vs. Brilliance
Table percentage affects these qualities.

Brilliance refers to brightness ~ the ability to reflect and return light through the top of the diamond
Fire refers to dispersion ~ the ability to break up light into the individual colors of the spectrum. Fiery diamonds also tend to favor scintillation ~ a dancing of light within the stone.

In a perfect world, one cut would maximize both fire and brilliance. In reality, they are opposing features. As the table percentage increases, fire is traded off for brilliance. In the evolution of  diamond cutting, the current ideal is close to the mid-point on fire and brilliance, but ultimately the choice is yours.

Beyond proportion: some features of poorly cut stones

  • A watery look and white circle called a fisheye when viewed from the top, warn of a shallow cut and pavilion problems.
  • A dark appearance in the table and other facets, "nailheads," warn of a deep cut and pavilion problems.
  • A very thick girdle adds weight without enhancing sparkle and appearance, and can make it hard to set the diamond. This is more common in stones that are close to the next cost-per-carat increase.
  • A knife-edge (extra thin) girdle chips easily.
  • In fancy cuts (marquise, oval, pear), watch out for a dark bow-tie shaped area where light escapes.
  • Symmetry and finish problems can include: misshapen and extra facets, off-center tables and culets, wavy and out-of-round girdles, misaligned crown and pavilion facets, surface blemishes, and poor polish.
  • A "natural" (intentional uncut face) rarely affects value.

The Evolution of Cut

Old Mine Old European
Transitional Brilliant Modern Brilliant

Old Mine: These diamonds generally date from the 1700's to 1870. The cut is characterized by a squarish outline, high crown, small table, and very large, open culet. They tend to have only crude symmetry and faceting. Unless an OMC is needed as a replacement, to match others in a piece, a recut is usually recommended.

Old European: This cut prevailed from 1870-1920. It is usually round, with a relatively small table, proportionately more height above the girdle than modern brilliants, and an open culet (the tip cut off). In assessing an OEC diamond, those cut prior to 1900 often have too much culet removed, with a loss of sparkle and value. From 1900 onward, the amount cut from the culet was usually slight, sometimes not even perceptible without magnification. These stones rival the beauty and sparkle of today's well-made round brilliants, the cut which took over by 1930. For those who favor fire over brilliance, an OEC from an estate jeweler could well be the diamond of choice.

Round Brilliant: Sometimes called a "full cut." Has 57 facets plus the culet.

| Carat Weight | Color | Clarity | Shape | Cut |


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