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. All these factors come together to determine the cut grade of the diamond. Each diamond shape and size has an ideal cut proportion. If you're looking for an ideally vut diamond, simply ask one of gemologists and they can point out a few diamond options that have ideal proportions.


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. This cut category represents the top 35% of gem quality diamonds. Avoid these diamonds as they will not make for sparkling jewelry.

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. The top 15% of gemstone quality diamonds are Very Good cut. Very Good cut diamonds can be a great choice if looking mazimize value on the other factors.

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. The top 25% of diamonds have a Good cut grade. Good cut diamonds can be a good blend of value and size, however be careful and always ask a gemologist to assess the particular diamond for you before you make a decision.

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. This premium category represents the top 3% of all diamonds. Excellent cut diamonds are increasing with improvements in manufacturing technology. An excellent cut diamond is always a good choice regardless of diamond shape and size.

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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. The better and more uniformly a diamond is able to reflect and showcase light,the better of a diamond it is as it will sparkle more in your jewelry.

light reflecting off the surface of the diamond

Reflections

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

Refraction

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. With a diamond that is cut well, light refelcts perfectly within the diamond.

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

Dispersion

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. Other gemstones and diamond simulants typically do not have the same beautiful dispersion that diamonds have. Therefore, diamonds are considered to be the most popular choice for engagement rings and jewelry.


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. These cuts are elegant but because they have fewer facets do not reflect light as much as brilliant cut diamonds. While both diamonds have unique beauty, it is important to consider which type of diamond sparkle you want while picking a diamond cut.

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. In order to have an excellent cut diamond, all the aspects of the diamond must be cut in the ideal way. Here are the part that make up a diamond:

table facet of the diamond shaded

Table

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

Depth

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

Crown

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

Pavilion

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

Girdle

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

Culet

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.


Diamond Brilliance: What Makes Sparkle

When diamonds are found in the earth whether as alluvial deposits or within rough, they are certainly not the well-cut shining gems that we see in jewelry. When found in the earth, diamonds actually have an opaque and rough skin on top. When polishing and cutting a diamond, this exterior skin is removed. In addition two important factors are considered. First is the refractive index of the diamond which is responsible for the brilliance of the diamond. And second is the dispersive power of the diamond which allows it's ability to split white light and reflect back additional colors. The term scintillation brilliance is applied to the number and arrangement of light reflections from the internal facets that shows of sparkle as the wearer of the diamond moves around. A diamond's fire is determined by the cut's crown height and angle and the size and number of facets on the diamond. Therefore, the angles, cut and faceting of the diamond are all essential in determining the beauty of the diamond. When considering cut, be sure to also look at the proportions of the diamond and it's measurements. This can oftentimes help you decide between two diamonds in the same cut range.

A diamond's brilliance is rather a complex integration of angles and proporations. It represents the diamond's light return based on how the light enters, bounces around and returns to the human eye. The brilliance consists of multiple factors based on faceting, and patterns. Poor light return from a diamond (diamonds that exhibit light leakage) will lack optimal beauty. They will look, darker, duller or lifeless. The best way to think about it is a window. A dirty window will make it look dull, dark or murky outside. Also, misshapen windows (concave or bent), will affect the outdoor visibility. Diamonds are similar in that without perfect faceting, the light's performance and visibility are reduced.

Fire described flashes of color resulting from spectral separation or dispersion of white light into primary colors. Fire is the reason you see blues, oranges, reds, purples, etc. in a diamond. The more colors, the better. This is similar to how light produces a visual rainbow after or during rain.

So how is the the brilliance or fire optimized in a diamond? Well, it's typically a combination of tablet facet, crown angle, girdle, pavilion depth, culet and total depth. A rule of thumb is a culet should always be closed. A table shouldn't be too large or small. Total depth shouldn't be too deep or shallow. The girrdle shouldn't be thick or very thin. And there is an inverse relationship between crown angle and pavilion angle. If the crown is steep, the pavilion angle should be shallow and vice versa. We recommend diamonds with steeper crown angles and smaller table facets for the highest degree of brilliance or sparkle.


Diamond Cut History

Within nature and in their rough state, an unpolished diamond looks significantly different than a polished diamond. In it's rough state, diamonds are not commonly used in jewelry. Initially, diamonds were simply polished in their natural shape to reveal some of the sparkle within. As years went by, cut and polish techniques were imporved to enable more light to refract and reflect within the diamond. One common diamond cut that developed in the 14th century was the point cut, in which the diamond simple took the shape of a triangle placed upon an inverted triangle. This closely mimiced it's shape in nature. Over time the importance of a culet and table was realized so that the diamond would have a more palatable shape for jewelry. However, these advancements did not create the sparkle, fire and scintillation that is seen in modern cut diamonds. In 1476 a master diamond cutter experimented with adding triangular facets to diamonds to unleash their sparkle and thus the modern diamond was on it's way to being shaped and formed. This developed into the rose or antique cut which has large and open facets that may not be symmetrical. The asymmetry is a result of diamonds being cut to preserve weight as well as hand-cutting techniques. Eventually in the 1900's a master diamond cutter named Tolkowsky acertained better diamond proportions taking sparkle and fire into consideration to produce a diamond with extraordinary brilliance. The modern brilliant cut diamond is a result of his efforts and research. Over time, diamond cut became standardized due to the efforts of diamond cutters to adhere to similiar practices and diamond cut grades. Today, diamonds are machine cut to ensure maximum precision. Varying grades can be the result of the nature of the rough diamond as well as derire to preserve carat weight and minimize the appearance of inclusions.


The Diamond's True Size or 'Spread'

Spread or the diamond's measurements is the simplest concept for a buyer to grasp. Diamond's with greater spread (less total depth) mean the diamond looks larger. Most cut grading systems don't account for spread, which is interesting given the fact that it is the easiest cut-related metric to examine.

While larger looking diamonds are not necessarily more sparkly, they are considered more desirable and often have a premium. Two diamonds can have the same carat weight, but the one with larger measurements has more spread. Spread is not related to the diamond's carat weight. It is actually the total depth percentage that dictates the spread. That means the width/length against the height. In general, we recommend diamonds in the excellent cut range with the maximum measurements so you can achieve the best of both worlds. You may pay a slight premium for this but it will be well worth it as you will be getting the best of sparkle and size.


Expert Buying Tips

Try and maximize on the cut score and grade of the diamond. This represents the sparkle of the diamond and can help mask (or make up for) lower clarity grades, color tints, or smaller than desired carat weights. You may find value in a VG cut diamond that have most of the technical aspects of a Excellent cut diamond, but missed the cut off by a technicality such as a thick girdle or larger table facet.