Diamond Cut

Diamonds are cut to maximize the sparkle, fire, brilliance and overall visual beauty of a diamond. The cut is a measure of light performance as light hits a diamond. Before a diamond is cut and polished, it is known as a rough diamond. The skin of the rough diamond is opaque and often difficult to see through. Rough diamonds have little to no sparkle. This is because they lack facets or faces that bounce and reflect light. Diamonds sparkle is a result of light performance. As light hits a diamond, it penetrates the diamond, bounces around and reflects within the diamond and ultimately returns light to your eye. That is the sparkle that you see.The cutting of a diamond directly impacts the amount of light performance achieved. The angles, locations, sizes and shapes of facets will determine the diamond sparkle.

Cut Scale: The Factors

Once a diamond has been cut and polished, it’s cut can be graded. GIA grades cut base precisely measuring the angles and sizes of the facets of a diamond. These include the diamond’s Table, Depth, Girdle, Pavilion, Crown and Culet. Polish and Symmetry can also place a small role.

The Cut Scale

gia cut grading scale showing diamond light performance and sparkle from Excellent cut, Very Good cut, Good cut and fair/poor cut

Fair & Poor: Diamonds with significant light leakage earn a Fair or Poor grade. These diamonds tend to leak noticeable amounts of light from being too deep or shallow in height. These have little brilliance and are less visually appealing. Fair or Poor cut diamonds do not meet Four Mine’s minimum light performance criteria.

Very Good: Very well cut diamonds that capture almost all the potential of the diamond. Very brilliant with minimal light leakage. Diamonds cut often intentional cut to achieve a Very Good grade so that can improve the other characteristics of the diamond such as Color, Clarity or Carat.

Good: Well cut diamonds that capture light and possess high degrees of sparkle. Good cut diamonds have some light leakage, but overall shine bright. These diamonds can have noticeably larger or even smaller measurements than perfectly cut diamonds of the same shape. Cutters may intentionally cut to Good proportions to achieve a particular look or style.

Excellent: The highest grade representing the top diamonds in the world. Diamonds with an Excellent cut grade are masterfully crafted and precisely cut to unleash the maximum sparkle and brilliance of a diamond. Little or no light leakage occurs as light passes through a diamond.

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Light Performance

A diamond’s cut reflects the brilliance and sparkle you see from it. That sparkle is light performance. Light performance is made up of factors such as reflection, refraction, and dispersion.

light reflecting off the surface of the diamond


When a diamond is rocked and tilted at different angles, some light reflects on the surface of facets rather than bouncing around inside the diamond. This is known as reflection. Typically, about 17% of light is actually reflected by the diamond. Reflection should be balanced. When facets are too large, we can see reflections either strengthen or weaken too much, which will cause the diamond to seem dull.

light refracting inside the diamond can creating fire and brilliance


The ideal diamond is cut such that light enters, bounces around, bends and ultimately exits from the top of the diamond. This concept is known as refraction. Diamonds score a 2.41 on the refractive index, which is high and gives diamonds their sparkly characteristics. With ideal cutting, the refraction is most noticeable.

Dispersion occuring within a diamond to produce the primary colors by light performance


Ever noticed that a diamond isn’t black and white; rather you can see all the colors of the rainbow reflecting from within the diamond? Well, that’s a result of dispersion. As light bounces around in a diamond, bends and then exits back to your eye, a diamond’s dispersion is measured at 0.44. It is most commonly known as the fire within a diamond. The visibility of all these colors is what gives diamonds a unique beauty.

Finish: Polish, Symmetry and Facets

Other factors that affect the cut grade are Polish, Symmetry and faceting. These are the finish of a diamond. Diamonds are typically cut in two ways: step cuts and brilliant cuts.

diamond sketch for a step cut

Step cuts, such as Emerald cut diamonds and Asscher cut diamonds, have sparkle or fire. They have facets that look like a staircase and are a bit simpler in presentation. They are considered very elegant and maximize the diamond’s scintillation.

diamond sketch for a brilliant cut

Brilliant cuts, most commonly Round cut diamonds or Princess cut diamonds, have maximum diamond sparkle. They possess more facets than step cuts and the facets are triangular and kite-shaped. Brilliant cuts have a high degree of diamond sparkle and maximum the fire and scintillation of a diamond.

The other two attributes of finish are polish and symmetry. Both of these are a result of the manufacturing process. The polish of a diamond is how cleanly smooth the facet surfaces are. If small striated polish lines remain, it may affect light performance and therefore, diamond cut. The other attribute is symmetry. Symmetry is simply the pattern and evenness of the size, shape and location of facets. If the location of a facet is incorrect, the performance of light and therefore the cut grade can be affected. For example, an off center table facet may reduce diamond sparkle.

Pricing Effect

Like the other diamond C’s, Cut grade can have substantial implications on pricing. Today, we see the highest number of Excellent cut or perfectly cut diamonds. The improvement of diamond manufacturing technology allows diamantaires to be more precise in cutting practices. With round cut diamonds, an Excellent cut can have a 5%-10% premium over the next grade, Very Good cut. The same applies from Very Good to Good.
Fancy shaped diamonds (shapes other than Round cut) do not have GIA assigned cut grades. This is because with fancy shapes, diamonds can have a variety of shapes and lengths/widths all the while still maximizing brilliance and sparkle. Four Mine factors in a variety of diamond attributes to assign its own grading standards to fancy shapes.

Selecting Cut Grade

Cut is often consider the most important of the 4 C’s of diamonds (carat is more of a preference, not an art or science). When selecting a diamond, it will certainly important to ensure light is not lost. Excellent cuts are most premium and Very Good cuts offer more value. The differences in sparkle are quite subtle, but they are noticeable when compared side by side. We recommend maximizing on the Cut grade, if possible.

Fancy shapes have less restrictions because beauty is in the eye of the beholder. Still, you can often safely go a grade lower with non round diamond shapes. Excellent cut fancy shapes are fairly rare.

In the end, it’s your decision and you must remember there are plenty of other factors that influence a diamond. You must choose which factors/attributes matter most to you.

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Parts of a Diamond

The anatomy of a diamond consists of several parts engineers in precise locations to maximize diamond brilliance. The diamond’s cut grade is actually determined by examining these parts in conjunction because one part can be perfect and another flawed. Here are the part that make up a diamond:

table facet of the diamond shaded


The diamond table is the largest and top-most facet of a gemstone in which light penetrates and escapes with sparkle and fire. The ideal range for the table facet in a round cut diamond is between 54% and 61%. A larger table can make a diamond look larger, because the reflection (not refraction) may be greater.

a sketch of a diamond representing the depth with arrows


The diamond’s depth is the distance from the table to the culet. Along with table, depth is a critical attribute in determining a diamond’s cut grade. Diamonds that are cut too deep (larger distance from table to culet) will result in light leakage. Deeper diamonds will also look visually smaller than other diamonds that may possess the same carat weight. This is because the carat weight is held in the depth of the diamond. Diamonds that are cut too shallow (shorter distance from table to culet) will also result in light leakage. Shallow diamonds tend to look larger than deeper diamonds because they spread the carat weight wider to the sides of the diamond, giving it more surface area. A shallower diamond can be a great thing, but the trade off is possibly light leakage or sparkle. The ideal range for a round cut diamond’s depth is between 59% - 62.9%

the crown of the diamond shaded


A diamond’s crown is the top part of the diamond above the girdle. It is called the crown because it is at the height of the diamond and from a profile view, it resembles an upside down crown. The crown is where the maximum amount of light enters and escapes. The crown must be angled appropriately in order to bounce and reflect/refract light for maximum diamond sparkle and brilliance. A shallow crown or crown angle can look like a flat top, increasing light leakage. A heavy or steep crown angle can reduce light penetration and decrease the diamond’s sparkle. The ideal crown angle for a round diamond is between 32.5 - 35 degrees.

the pavilion of the diamond shaded


The diamond pavilion is the bottom part of the diamond below the girdle. Like the crown, the diamond’s pavilion must be correctly faceted and angled in order to refract light. Once light enters the crown, it is the pavilion’s job to bounce light back to the eye, creating a sparkle effect. In the pavilion angles are too deep or shallow, light will fall through. Sparkle is merely the bounce back of light. If the light doesn’t bounce back, sparkle is lost. The ideal pavilion angle for a round diamond is 40 - 41.6 degrees.

The Girdle of the diamond shaded


The girdle of a diamond is the thinner center portion between the crown and pavilion. It is the widest point of a diamond. Girdles can be polish, faceted or unpolished. Modern diamonds tend to have slightly thinner polished and facets girdles. The thickness of a girdle can have great implications on the cut grade of a diamond. The ideal girdle range is thin - slightly thick. Very thin girdles can chip or break during the setting process and very thick girdles can create girdle reflections within the diamond, thereby reducing the diamond’s sparkle.

the diamond's culet is shaded in the diamond icon


The culet of a diamond is the bottom-most point of the diamond. It is where the diamond’s faceting meets in the center below the table to close or seal it off so light doesn’t fall through and is instead bounced around inside the diamonds and reflected back. It is most common to find pointed culets graded None. Diamonds with medium or large culets tend to leak light and are typically found only in old mine or old european cut diamonds. While it is very difficult to chip or break a diamond, because the culet is the thinnest part of the diamond, it can chip from blunt impact or trauma.