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
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.
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
Table Size = Diameter of the flat top facet,
corner to corner
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"):
Basic Tests for
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.
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:
Table Percentage -- Divide the diameter of the table by the diameter at the girdle, and compare the result to this chart:
Fire vs. Brilliance
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
The Evolution of Cut
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.