The Four C's: Cut


Cut actually refers to two aspects of a diamond. The first is its shape (round brilliant cut, marquise cut, etc) which is explained below, and the second is how well the cutting has been executed which we will discuss here. The cut or “make” of a stone is one of the most important of all diamond characteristics, and among the hardest to judge. The proportions of a stone as well as its polish and precision of faceting determine how much of the diamond’s potential fire and beauty may be released.

It is a diamond cutter’s job to maintain a balance between retaining the maximum weight from rough stones and cutting the finest possible diamond at the expense of “yield.” Some diamonds are cut exceedingly deep or shallow, or are shaped to conform to the original shape of the rough stone. A poorly made stone tends to result in a higher yield (less waste) from the rough while a better made diamond may “waste” more of the rough. A typical well-cut round diamond typically weighs only about 45% of the original weight of the piece of rough the cutter started with. This is why better cut diamonds command a premium, and why Ideal Cut round diamonds are the most costly of all.

Ideal Cut Diamonds

An ideal cut diamond is a round brilliant cut diamond cut according to the strictest, “ideal” parameters of proportion and finish. It should be noted that the “ideal” and “premium” grades only apply to round brilliant cuts. There is considerably less agreement about the best combination of proportions necessary for optimum appearance in fancy (any non-round) shapes.

The way a diamond is cut profoundly influences its sparkle, fire and brilliance, as well as its perceived size and even, to some degree its apparent color. In order to maximize the diamond’s brilliance it must be well polished and cut in a geometrically precise manner. This means properly aligning the facets so light will enter the diamond and reflect back through the large top facet, or table of the diamond. For the parameters of an Ideal Cut/Excellent cut diamond, see the short cutting feature definitions below the diamond diagram.

The most basic measurements of a diamond, expressed in millimeters actually describe the following: minimum width, maximum width (or length), and depth. These measurements are important in matching stones for use in earrings and other jewelry and for evaluating the cut quality of a stone. All other features describing the cut of a diamond, with the exception of polish, are based on the stone’s measurements.

GIA Anatomy of A Diamond

Diamond Anatomy

Start by learning the “anatomy” of a diamond. The proportions of these are critical measures in determining the quality of a diamond’s cut.

  • Polish and Symmetry:Symmetry refers to the overall uniformity of the cut of a diamond. Symmetry is based on the diamond’s proportions, the relation of one facet to another. A diamond with very good to excellent symmetry can be more attractive than a less symmetrical stone. Stones with poor symmetry can actually appear off-centered or noticeably out of round. Although most non-experts could never notice subtle differences in polish or symmetry, noticeably asymmetrical stones denoting poor symmetry are less attractive and less valuable – just as a poor polish may detract from the brilliance of a diamond and may actually leave slight streaks on the surface. Below are some cut characteristics, and the effect they have on the overall quality of the diamond. Polish grades are based on the final finish applied to the facets and facet junctures by the cutter. Well-polished diamonds permit maximum passage of light and prevent potentially streaky surfaces. Ideally, you would want a value of Excellent to Very Good for both polish and symmetry.

  • Table / Table Percentage:The table is the top-most and generally the largest facet of a diamond through which much of the light both enters and exits. A table that is too large or too small will reduce the overall dispersion of a diamond’s brilliance. In combination with other factors, the table percentage is a significant component of a diamond’s overall cut quality and value. Ideal Cut / Excellent Cut parameters for the table percentage should be between 53%-62%.

  • Depth / Depth Percentage:The depth is a measurement of the distance from the table to the culet (bottom-most point). A depth that is too shallow or too deep will allow light to escape through the bottom of the stone, reducing the stone’s overall fire and brilliance. Depth percentage is a significant component of the diamond’s overall cut quality and value. Ideal Cut / Excellent Cut parameters for the depth percentage should be between 59-62.5%.

  • Crown / Crown Angle:The crown is the top portion of the diamond that lies above the girdle. Crown angle is a measurement that relates the depth of the crown to the diamond’s overall depth. The Ideal Cut / Excellent Cut parameters for crown angles should be between 33–35 degrees.

  • Girdle:The outermost edge of a diamond; it can be unpolished or polished and faceted and of varying thickness. Extremely thin or extremely thick girdles are less desirable than more moderate girdles. The girdle is generally where the diamond is held in a setting. Girdles may be laser-inscribed with serial numbers, names, etc. without affecting the diamond’s overall brilliance or value.

  • Culet:The bottom-most facet or point of a diamond. Unless the culet is abnormally large, it generally has no impact on the value of a diamond. The Ideal Cut / Excellent Cut parameters culet size should be None to Very Small.

  • Length / Width Ratio:Applicable for fancy shapes (non-round). As you look down at the stone, the length/width ratio describes the shape of the profile. Although some ratios are generally viewed as more desirable than others for each fancy shape, the length/width ratio that is right for you is a matter of personal preference. For example, the ideal length to width ratio for marquise cut diamonds is generally considered around 2:1 (1.8:1 to 2.2:1 would certainly be acceptable, according to personal preference.)

Cut Impact on Beauty and Price

Impact On Beauty: A diamond’s cut will most certainly influence its fire (the lovely rainbow colors that flash from within) and brilliance (the liveliness and sparkle), as well as its perceived size and even, to some degree its apparent color. The diagram below illustrates how different cuts reflect light in different angles. A diamond must be cut in a geometrically precise manner to maximize its brilliance. On a classic round brilliant-cut diamond, 57 or 58 facets must be precisely aligned so light will enter the diamond and reflect back through the large top facet, or table of the diamond. In order to enhance profit potential, recently many diamond sellers have sought to brand their diamonds by changing slightly the facet pattern of a classic cut and trade-marking their new creation with a unique name. They can then claim that it is somehow superior to the original, and is therefore worthy of a premium price.

The percentage measurements for depth, height and crown are important due to their impact on how light passes through a diamond. Light should enter and exit a diamond through the top facets. A cut that is too shallow or too deep reflects it through the pavilion facets, and lets the light “leak” out of the bottom or side of the gem. Please keep in mind that earrings and pendants do not generally receive the same scrutiny as the feature diamond in a ring. For that reason, you might consider being a bit more open to a slightly lower cut grade in exchange for greater size in these items.

Impact on Price:When purchasing any diamond, carefully consider the grade of the cut. For round brilliant diamonds: excellent, ideal, premium, very good, good, fair, or poor. For all other cuts: very good, good, fair, or poor. Obviously, the cost of a diamond with will increase with the quality of the cut.

Shapes and Styles of Diamonds

Today we can choose from many different stone shapes (also referred to as “cuts”) ranging from the classics to newer silhouettes that appear as diamond cutters endeavor to create new looks.

Listed below are the eight most popular and traditional cuts.

  • Round Brilliant – the most classic cut

  • Marquise – an elongated brilliant-cut stone with a point on each end

  • Cushion – defined by its rounded corners and sides, and may vary from squarish to oblong

  • Princess – typically a four-sided square to slightly rectangular brilliant cut

  • Radiant – a rectangular to squarish octagonal diamond

  • Emerald – a traditional octagonal cut usually rectangular

  • Asscher – basically a square emerald with some subtle differences in the facet pattern

  • Pear – combines the brilliance and form of a round stone with the elongated elegance of a marquise

  • Oval – reminiscent of the round brilliant cut, both in sparkle and shape

  • Heart – more fanciful cut, shaped just as it sounds

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