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Diamond Cut Grades - Education & Buying Guide

A diamond's cut is the most critical of the 4Cs because it's what gives the diamond its brilliance, sparkle, and fire - the diamond's three main attributes. When people talk about "brilliance," they are referring to the amount of light a diamond reflects, "fire" describes the way the light disperses and how the diamond shows off the different colors of the spectrum, "sparkle" - also known as "scintillation" - defines how much the diamond shimmers when you move it around in the light. When light enters the diamond, it is refracted and bounces back out in a rainbow of colors.

The way a diamond is cut will have the biggest effect on how the diamond catches and interacts with light. It is the ultimate expression of a craftsman's skill in transforming a rough diamond into a breathtaking gem. If the diamond is too shallow and not cut right, some of the light will be lost out of the bottom. One that is cut too deeply will lose light out the side of its base. An Ideal cut diamond will reflect most of the light through their table or top surface.

The cut of a diamond refers not to its shape, but to the balance of proportion, symmetry and polish achieved by the diamond cutter. The extent of how well the diamond is cut is directly related to the diamond's overall beauty. When a diamond has been correctly cut, the diamond's ability to reflect and refract light is greatly enhanced. By understanding the way that light moves through diamond crystals, modern diamond cutters have established a specific set of proportions and angles that are known to harness the diamond's internal brilliance and to show it in its best light.

It's important to note that the cut depends on the diamond's shape while it does not describe the shape. The most popular shape is the round brilliant diamond that is cut with 57 facets. When the culet is flattened into a facet, a round diamond will have 58 facets.

Other shapes are usually referred to as "fancy shapes," and include princess, emerald, asscher, marquise, oval, radiant, pear, heart and cushion. Each diamond shape has its own set of guidelines that determine the quality level of its cut.

As mentioned, often confused with a diamond shape, the cut is actually the grading that determines how well the diamond sparkles. It encapsulates Brightness (white light reflecting from the top surface), Fire (flares of color) and Scintillation (flashes of light).

The Effects Of Light On A Diamond

The science behind a diamond's brilliance depends on its great ability to bend, slow and direct light as it passes through. The cut of a diamond determines how well the diamond is able to re-direct the light back through the surface of the diamond. Light travelling at about 186,000 miles per second, when passing through a diamond is reduced to about 77,000 miles per second, close to the maximum for any other transparent substance. 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 jewellery.

Reflection

Reflection

Brilliance.

Dispersion

Dispersion

Fire.

Refraction

Refraction

Scintillation.

Effects of light on a diamond.

Reflection (Brilliance)

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. Brilliance, or brightness, refers to the white light that is reflected back to the eye from the diamond. Light enters through the top of the diamond (the table), is broken down into a rainbow of spectral colors, and is reflected back and forth in the interior of the gem by bouncing off the mirror-like facets. Light exits through the table, recombining as white light.

Dispersion (Fire)

Dispersion is the rainbow of colors that is reflected back to the eye from the diamond. Light enters through the top of the diamond, is broken down into a rainbow of spectral colors, and is reflected back and forth in the interior of the gem by bouncing off the mirror-like facets. When it leaves through the crown, it stays separated and reaches the eye in flashes of color. 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 jewellery.

Refraction (Scintillation)

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. Scintillation is the play of light you see with movement of the diamond, demonstrated by sparkling on the diamond's surface. A diamond is evaluated on its ability to reflect and refract light in all directions.

Brilliance, Fire & Scintillation


Brilliance

Diamond Brilliance

Reflection.

Fire

Diamond Fire

Dispersion.

Scintillation

Diamond Scintillation

Refraction.

Diamond brilliance, fire & scintillation.

Diamond Cut Grading

As mentioned, the quality of cut is determined by how well the symmetry, polish, and proportions of the diamond produce the most attractive balance of the three different types of reflection. Several proportion factors have the most immediate impact on a diamond's ability to reflect light correctly. The table size and depth of a diamond relative to the diameter greatly impacts the light return from a diamond. A well cut diamond is proportioned so that most of the light entering the gem exits back through the top of the diamond, perfectly balancing the white light (brilliance) with intense flashes of fire (dispersion). A poorly cut diamond, with facets cut only a few degrees out of alignment, can result in light exiting through the bottom of the diamond, known as light leakage, instead of from the top where it is visible. This creates a diamond with dulled brilliance from poor light performance within the gem, making the center of the gem look dark.

The GIA have developed a grading system, which take these and other important factors into account to provide a scientific assessment of a diamond's sparkle. Most reputable jewellers use the GIA classification of Excellent, Very Good, Good, Fair and Poor grades to help customers assess diamond quality. The images and descriptions below displays the GIA grading classifications relating to cut:

Diamond Cut Scale - Light Affect On Diamond Cut Grades



Excellent (or Ideal) Cut

Excellent Cut Diamond

Highest possible level of brilliance. Maximum amount of light reflection, brilliance and fire.

Very Good (or Fine) Cut

Very Good Cut Diamond

Minimal light leakage. Very good light reflection brilliance and fire.

Good (or Well) Cut

Good Cut Diamond

Respectable level of reflectiveness. Allows a small amount of light to leak out the sides and bottom of the diamond.

Fair (or Shallow/Deep) Cut

Fair Cut Diamond

Weak ability to reflect light. Allows some light to escape through the sides and bottom of the diamond, effecting its fire and brilliance.

Poor (or Shallow/Deep) Cut

Poor Cut Diamond

Weak ability to reflect light. Allows much of the light to escape through the sides and bottom of the diamond, minimizing brilliance and fire.

Select Diamond Cut

Excellent Very Good Good Fair Poor

Light affect on diamond cut grades.

Diamond Cut Chart

GIA, considered to be one of the most respected laboratories for grading natural diamonds, uses the following language on their certificates to grade cut for round diamonds: Excellent, Very Good, Good, Fair, Poor. A GIA Excellent cut will be listed as either Ideal or Super Ideal with some reputable jeweller's.


Cut Cut Description
Excellent Excellent cut diamonds provide the highest level of fire and brilliance. Because almost all of the incoming light is reflected through the table, the diamond radiates with magnificent sparkle.
Very Good Very Good cut diamonds offer exceptional brilliance and fire. A large majority of the entering light reflects through the diamond's table. To the naked eye, very good diamonds provide similar sparkle to those of Excellent grade.
Good Good cut diamonds showcase brilliance and sparkle, with much of the light reflecting through the table to the viewer's eye. These diamonds provide beauty at a lower price point.
Fair Fair cut diamonds offer little brilliance, as light easily exits through the bottom and sides of the diamond. Diamonds of a fair cut may be a satisfactory choice for smaller carats and those acting as side stones.
Poor Poor cut ciamonds yield nearly no sparkle, brilliance or fire. Entering light escapes from the sides and bottom of the diamond.

Diamond cut chart.

The cut grading currently only applies to round diamonds as they are technically easier to measure in terms of light performance. Other shapes - such as princess cuts, cushion cuts, emerald shapes, do not have a cut grading on their certificates.

Cut grades range from Excellent, Very Good, Good, Fair and Poor. The grading takes into account various attributes of the diamond that cannot be seen or measured with the untrained eye. An excellent cut grading will have the best light performance, mainly influenced by the relationship of surface table and the depth of the diamond (not too deep or too shallow).

It is very hard to see the difference between an Excellent and a Very Good cut diamond as the direction of light is the same in both cut gradings. We therefore recommend you try to stick with an Excellent or Very Good cut, but if needed to fit the budget, a Good cut can offer an excellent value alternative without any major compromises. Just make sure you are not on the "Deep" side or you will end up with a diamond that looks smaller than the actual carat weight.

Diamond Cut Chart Description


Excellent (or Ideal) Cut

Diamonds classified as Excellent or Ideal cut offer the most sparkle, dispersion and fire and are considered to be of the highest quality. Light moving through an ideal cut diamond bounces almost fully back out the top of the diamond and brings its brilliance into view.

Note - 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.

Very Good (or Fine) Cut

Diamonds classified as Very Good offer slightly less brilliance and scintillation than the excellent cut. However, as the difference between the two is almost indistinguishable to the unaided eye, very good cuts offer better value for money than excellent cut diamonds.

Note - 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 (or Well) Cut

Diamonds classified as Good, usually allow some light to escape during the reflective process, although once again, the difference between this and the very good cut diamonds is small therefore good cuts offer great value for money and make for a more affordable option.

Note - 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.

Fair (or Shallow/Deep) Cut

Light moving through a shallow cut diamond is lost out of the bottom of the diamond and the lack of light play makes shallow cut diamonds appear lifeless. The poor sparkle performance of diamonds classified as Fair cut may be noticeable to the untrained eye, and are for this reason also less costly.

Poor (or Shallow/Deep) Cut

Light moving through a deep cut diamond escapes out from the sides, darkening all or most portions of the diamond. The poor sparkle performance of diamonds classified as Poor cut may be noticeable to the untrained eye, and are for this reason also less costly.

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

Diamond Cut - Cut Grades Affect On Diamonds



Excellent (or Ideal) Cut

Excellent Cut Diamond

Very Good (or Fine) Cut

Very Good Cut Diamond

Good (or Well) Cut

Good Cut Diamond

Fair (or Shallow/Deep) Cut

Fair Cut Diamond

Poor (or Shallow/Deep) Cut

Poor Cut Diamond

Select Diamond Cut

Excellent Very Good Good Fair Poor

Cut grades affect on diamonds.

Cut Grades Affect On Diamonds Description


Excellent (or Ideal) Cut

The diamond, which has an even pattern of bright and dark areas, scores in the top category for all grade-setting determinants.

Very Good (or Fine) Cut

This diamond's grade is determined by brightness, scintillation, and polish. Although no individual proportions would necessarily cause its brightness or scintillation to perform poorly, the combination of this particular set of proportions leads to increased darkness in the pavilion mains.

Good (or Well) Cut

This diamond's grade is limited by its scintillation. In this case, the somewhat shallow pavilion angle produces dark pavilion mains.

Fair (or Shallow/Deep) Cut

This diamond's grade is limited by its scintillation. The combination of a shallow crown angle and a somewhat shallow pavilion angle leads to a face-up appearance with a lack of contrast and general darkness.

Poor (or Shallow/Deep) Cut

This diamond's grade is limited by its weight ratio. Although most of the proportions for this diamond are fairly standard, the extremely thick girdle greatly increases the total depth. Therefore, this diamond's diameter is much smaller than its carat weight would indicate.

Diamond Structure & Characteristics

From the crown to the culet, get familiar with the anatomy (structure) of a diamond and with the measurements that play a key role in determining its cut.

A diamond is made up of two key sections, the crown and the pavilion. Their structure and relationship to each other in the form of table and depth percentages have the biggest impact on the diamond's sparkle.

The round brilliant cut has been used as an example, because with most other diamond shapes ("fancy cut" diamonds) the cut grading is more complicated (hence why their cut grading does not appear on certificates such as GIA).

Structure

Round Cut Diamond Structure

Characteristics

Round Cut Diamond Characteristics

Round cut diamond structure & characteristics.

Diamond Structure & Characteristics Description

Diameter - Width of the diamond at the widest point of the girdle (in fancy cut diamonds, the smallest diameter is used).

Depth Percentage - 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% - 62.3%.

Table Percentage - 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 53% - 58%. A larger table can make a diamond look larger, because the reflection (not refraction) may be greater.

Crown Angle - 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 34.0 - 34.9 degrees.

Pavilion Angle - 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 42.8 - 43.2 degrees.

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.

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.

More On Diamond Cut Grading Factors

The cut is mainly influenced by the harmony between the table and depth percentages and crown and pavilion angels, either causing the diamond to dissipate light (poor cut) or optimally refract and reflect light (excellent cut). The depth and table percentages are calculated as follows:

Depth Percentage

Total Depth % = Total Depth (mm) / Average Girdle Diameter x 100.

Depth percentage - The higher the number, the deeper the diamond. The lower the number the shallower the diamond.

Table Percentage

Table % = Longest Table measurement (mm) / Average Girdle Diameter x 100.

Table percentage - The higher the number, the bigger the table looks. The lower the number, the smaller the table looks.

Table and depth percentages affect how light travels within the diamond and impacts a diamond's brilliance. If a cut is too shallow, light escapes out from the sides and the diamond loses brilliance. If the cut is too deep, light is lost from the bottom and the diamond appears dull or dark, see below:

Diamond Too Shallow

Diamond Cuts - Diamond Too Shallow

Shallow Cut - Poor Brilliance.

Depth percentage too shallow: 56.5% and below.
Table percentage too low.
Crown and pavilion angles too shallow.

Ideal Diamond

Diamond Cuts - Diamond Ideal

Ideal Cut - Most Brilliance.

Depth percentage is ideal for maximum sparkle: 59 - 62.3%.
Table percentage is ideal.
Crown and pavilion angles are optimal.

Diamond Too Deep

Diamond Cuts -  Diamond Too Deep

Deep Cut - Poor Brilliance.

Depth percentage too deep: 65% and above.
Table percentage too high.
Crown and pavilion angles too large.

Diamond cuts - The percentages above are specific to a round shaped diamond. The ideal proportions for other diamond shapes are all slightly different.

Diamond cut grades vs. table and depth percentages

Diamond cut grades vs. table and depth percentages.


Ideal cut diamond: Deep vs Shallow cut diamonds


What is an Ideal cut diamond?

Coined by a famous diamond cutter Marcel Tolkowsky back in the 1900s, the term "ideal diamond cut- refers to such proportions and angles when a diamond exhibits maximum brilliance and sparkle.

An ideal cut diamond has excellent polish and symmetry and reflects almost all the light that enters it. In other words. the ideal diamond cut is the highest possible standard which is also used as a benchmark for grading all diamonds.

While Tolkowsky's ideal cut standards serve as a global guideline for today's diamonds, some countries have made their modifications. There are at least six "ideal cut" standards being used today in the diamond industry but only three of them. including the one by Marcel Tolkowsky, are the most common.

What is a Deep cut diamond?

A diamond's total depth or height is measured from the surface of the table to the culet, in other words from top to bottom. This measurement is expressed as a percentage of the average girdle diameter.

Total depth percentage is one of the main factors when determining a diamond's cut grade. When a diamond has the right combination of total depth and girdle diameter, it is more capable of reflecting light which results in a stronger and more beautiful sparkle.

When a diamond's total depth is too high relative to the average girdle diameter, it is said that the diamond is too deep. As a result, the light doesn't reflect properly and the diamond looks less lively and have lower brightness compared with more proportional ones. In general, the deeper the cut of the diamond, the duller it looks.

Moreover, deep cut diamonds look smaller than ideal cut diamonds of the same carat weight when set in a mounting. This effect appears because the cutter sacrifices of the diamonds width to achieve a greater depth. When the diamond is set in a mounting, the additional depth is hidden in it so the only visible part is the diamond's top, which is smaller than of the ideal cut diamond.

Ideal Diamond & Fish-Eye Effect On Diamond

Ideal diamond & Fish-eye effect on diamond.

What is a Shallow cut diamond?

When a diamond's total depth is too low relative to the average girdle diameter, it is said that the diamond is too shallow or spread (spready).

Shallow diamonds lack depth compared to ideal cut diamonds which is why most of the light entering does not reflect through the table but leaks out from the bottom of the diamond (pavilion) sacrificing its brilliance and sparkle.

Moreover, shallow cut diamonds tend to exhibit a "fish eye effect", see image above, which occurs when the girdle of a diamond is reflected under the table facet. This phenomenon always detracts from the beauty of the diamond.

The reason for shallow cut diamonds is to make them look bigger as from above spready diamonds look wider than normal and it seems that they are of larger carat size. Sadly, some shoppers blindly focus on "bigger and cheaper" diamonds without thinking of the overall beauty of the diamond and the money they simply waste on such diamonds.

The Fish Eye effect on diamond

As mentioned, if a diamond is cut too shallow, the table facet of the diamond shows the internal reflections of the girdle. The resultant is a grey ring type or spot formation which is very unpleasant to look at and which diminishes the look and sparkle factor of the diamond. This particular spot resembles the eyes of a fish and therefore the name Fish Eye.

It does not matter if the same diamond which has the fish eye is graded with the highest color or clarity markings or and other attributes to its grading report. Such diamonds simply lack in terms of their brilliance and are not good looking at all.

Let us discuss in a little depth about the factors which lead to the formation of the fish eye effect in diamond. The effect generally depends on the factors mentioned below:

Due to the light travels, if the pavilion angles of a diamond are low then the diamond will naturally have lesser brilliance and will pronounce the cut defects that are included in the diamond. Now when light enters the diamond, the shallow depth of the diamond causes the rays to be reflected through the table from the girdle portion. This also means that if a diamond has a larger table facet and a thicker girdle, the fish eye effect of such a diamond would be even more severe.

Do shaped diamonds showcase fish eye effect?

Technically speaking, fish eye effect is present in every such diamond which has shallow pavilion angles and large table facets. It does not matter if the diamond is normal and round or if it is of any fancy shape. Hence, yes, fish eye effects do exist in fancy shaped diamonds like the pear, hearts, and ovals too.

Can such errors be recognized and avoided?

Yes, absolutely. These kinds of flaws do not require any expert supervision and are pretty recognizable to the naked eye. The best suggestion would be to avoid such kind of diamonds by examining every diamond one looks for to purchase.

Another good suggestion would be to prioritize the cut quality, i.e. the degree of precision to which the diamond cut has been done. One should look at every video of the particular diamonds during the process of selection and should always keep a sound and stern mind to look for any form of errors there might be.

Buying a perfect diamond for the loved ones is not a joke. Diamonds are a whole emotion themselves and hence should always be checked by one for the best possible quality; free from any kind of flaws and errors.

The Nail Head effect on diamond

Nail Head in a diamond is a visual effect that can be seen in a diamond if it is cut too deep. In such a case, the light instead of reflecting our eye reflects off the bottom of the diamond at a vague angle. Due to such a case, a dark shape appears in the center of the diamond; typically round in shape just like the head of a nail, hence, the name Nail Head.

This effect diminishes the outlook of the diamond and generally ruins the overall cut score of a diamond.

Nail Head Effect On Diamond

Nail head effect on diamond.


Diamond Ideal & Depth table for diamond shapes

As mentioned, diamond cut takes into account a diamond's proportions, the relationship between the size, shape, and angle of each diamond facet. A wide range of combinations are possible, and each diamond shape has a unique combination of ideal diamond depth and table percentages. Below are the Ideal Table & and Depth Percentages for diamond shapes:


Shape Ideal Table % Depth %
Round 53 - 58 59 - 62.3
Princess 67 - 72 64 - 75
Oval 53 - 63 58 - 62
Heart 53 - 63 58 - 62
Radiant 61 - 69 61 - 67
Pear 53 - 63 58 - 62
Marquise 53 - 63 58 - 62
Emerald 61 - 69 61 - 67
Asscher 61 - 69 61 - 67
Cushion 61 - 67 61 - 67

Diamond Ideal & Depth table for diamond shapes.

Diamond Girdle

The girdle is the outer edge of the diamond, where the crown (top) meets the pavilion (bottom). It is the narrow rim around the widest edge of the diamond. It's also sometimes referred to as the "setting edge" where a diamond is held when set in jewellery. The Girdle needs to be just right - it can't be too thin or too thick or it will affect the diamonds strength. If a girdle is too thick, it can affect the diamond's brilliance and it would also make it heavier (which, in turn, makes it more expensive). This is a great example of how knowing these diamond terms can help you get a higher value diamond at a good price.

When a loose diamond is sent for certification, it is measured at various points along the girdle to determine its thickest and thinnest points.

The girdle is most often rated as a range, such as 'Very Thin to Thick', to accommodate the variance between the thickest and thinnest point. Start by looking at the diagrams presented below. These diamonds both have great table and depth percentages and they appear to be exactly the same from a top view:

Girdle Thickness

Girdle thickness.

Girdle ratings and their characteristics can fall into one or more of the following categories:

Why Would a Diamond Cutter Cut a Thick Girdle?

The girdle is the widest part of the diamond, which equals weight, which, in turn, equals a higher justified price. This practice has been going on in the diamond industry for a long time.

The price difference between a 0.90 carat and a 1.00 carat is approximately $1,500 to $2,000. This is a very significant financial incentive for jewellers and cutters. In fact, over 50 per cent of the diamonds on the market today have thick girdles. This is an area that you won't find many other jewellers talking about.

Diamond Culet

The culet (pronounced cue-let) is the small area at the bottom of a diamond's pavilion. The culet can be a point or a very small facet sitting parallel to the table.

Every reputable jeweller displays the culet size as determined by the GIA, using the following scale:


Diamond Culet Scale
None
Very Small
Small
Medium
Slightly Large
Large
Very Large
Extremely Large

Diamond culet Scale.

Any diamond culet size of Medium or smaller will be invisible to the naked eye, and have no negative impact on a diamond's appearance. However, if a culet is Slightly Large or larger, it may allow light entering from the crown to pass straight through the culet facet, reducing the diamond's brilliance. This may also make the culet appear as an inclusion, or create a dead area on the diamond where the light is escaping through the bottom. An inclusion is an internal flaw in the diamond. The position, size, number, color, and reflectivity of a diamond's inclusions has a significant impact on its appearance and value. Clarity refers to the degree to which these natural flaws are present. Diamonds graded by the GIA and other labs have their clarity rated on a scale of F (flawless) to I3 (significant inclusions).

Other Factors Affecting Diamond Cut

Symmetry

When the facets of a diamond are well balanced and aligned, the diamond has symmetry, which is critical to creating optimal brilliance and scintillation. Errors in symmetry include facets that are not properly aligned, improperly shaped facets, or an off-centre table.

The grading methodology for symmetry can be further sub-divided into 2 types of categories - proportions and facets related.

Diamond Symmetry

Diamond symmetry.

A symmetry alteration that affects the alignment and balance of a diamond's facet structure is considered a proportioning flaw. These flaws are usually measurable and affect the diamond's overall appearance. These include the following:

On the other hand, facet related flaws are focused on the regularity of individual facets. Basically, similar facets should all be cut to equal sizes and regularity (i.e. all bezel facets should look the same, all pavilion main facets should look the same, etc.):

As mentioned, the relationship between the crown and the pavilion angles has an effect on the appearance of a diamond. A diamond's pavilion angle and depth must be correct to capture and reflect light optimally. A slightly steep pavilion angle can be complemented by a shallower crown angle, and vice versa. In diamonds with extremely deep pavilions, the whole surface of the table appears to be darker creating what is known as a "nailhead". Gems with more shallow pavilions often produce a "fisheye" effect due to the girdle's reflection in the diamond's table.

Fluorescence

When exposed to ultraviolet light, a small percentage of diamonds fluoresce, or emit a blue or yellow light. Fluorescence is caused by trace elements, usually boron, that seep into the diamond when it is created. While fluorescence does not necessarily affect a diamond's value, it is listed on a diamond grading report.

Polish

After a diamond is cut, each facet must be polished. The process can leave surface scratches or marks, which are like streaks left behind after a car is waxed. If a diamond has no scratches or very minor ones, the polish is of a high degree. Scratches, lines, burn markscreated by excessive heat, or rough girdles could downgrade the polish rating of a diamond and if significant, could affect the overall cut grading.

Hearts & Arrows Diamonds

During the 1980s in Japan, it was discovered that when a round brilliant diamond with exceptional symmetry was viewed from the bottom through a special viewer a pattern of hearts could be seen, and when viewed from the top showed eight gray arrowheads. Diamonds displaying such exceptional symmetry account for less than 1 % of all diamonds cut. The highest grades of polish, symmetry and perfect cutting angles allow it to reflect more light than a standard cut diamond.

Following the discovery, a special viewer was developed to display the Hearts & Arrows effect. The viewer is useful in determining the optical symmetry of a diamond, through the internal movement of light and reflection, depending on the size, shape and arrangement of facets. This optical symmetry is different from the Symmetry Grading on a laboratory grading report that assesses the 'tidiness' of facet intersections and placement. Diamonds with Hearts and Arrows patterns became very popular in Japan and spread as a trend in the USA during the mid 1990s.

Hearts & Arrows Diamonds

Hearts & arrows diamonds.

The Bow-Tie Effect Guide

The 4Cs identify most imperfections within a diamond, but there are a few other characteristics to look out for when buying a new gemstone. One of these features is the bow-tie effect, which can create a dark blemish in certain fancy diamond shapes. Although bow-ties may be hard to spot with an untrained eye, understanding what to look for can make the difference between a visible bow-tie and a sparkly diamond.

The bow-tie effect

When looking at a diamond, you may see a darker, bow-tie shaped space across the center of the table. This is a result of the bow-tie effect, and it's directly related to the diamond's cut. The bow-tie effect can impact diamonds of all cut grades, but the cutting process can determine how much it will affect a gem's shine.

Diamond Bow Tie

Diamond bow tie

The Bow-tie effect in diamonds causes and the shapes affected

Light refracting through the facets of a diamond creates fire and brilliance, giving us that mirror-like sparkle. When a facet is not cut properly, due to an inclusion or poor technique, it does not interact with light in a way that produces reflection. As such, the facet appears dark when viewed through the table of a diamond. With the bow-tie effect, specific facets suffer this lack of refraction, causing the bow-tie shape at the center of a diamond.

Unlike many common diamond issues, the bow-tie effect is a result of light blockage rather than light leakage. Light does not properly interact with the incriminating facets, even when the stone is turned or moved.

The bow-tie effect typically impacts diamonds with softer, elongated silhouettes, such as marquise, oval, pear, and heart-shaped diamonds.

Bow-tie effect grading

There is no precise grading for the bow-tie effect, but gemologists use a general scale to explain the severity of a diamond's bow-tie. The categories are as follows:

As mentioned, the categories are not incredibly defined, but understanding where a diamond's bow-tie effect falls on the scale can help you shop smarter.

The bow-tie effect impact on a diamond's value

Is the bow-tie effect a flaw created by a low-quality cut? Or, is it just another feature of certain diamond cuts? Because the bow-tie effect is not a quality you can find on a diamond report, it can be tricky to pinpoint how much a bow-tie affects a diamond's value. Additionally, some buyers like the bow-tie look, and so the inherent value of diamonds with the effect increases for these individuals.

The bow-tie effect impact on a diamond's GIA grade or report?

Overall, while bow-ties may be more visible in lower quality cut diamonds, they can appear in any diamond, as the GIA does not have a specific criterion for grading them.

In fact, you will not find any notes on a diamond's bow-tie in your GIA report. That is because a bow-tie's effect on a diamond's value is too subjective: some will like it, some will not. Focusing on the 4Cs, researching a diamond's characteristics in its grading report, and visually inspecting a diamond are the best tactics for avoiding a bow-tie.

Diamond cutters and eliminating the bow-tie effect

Although it's easy to assume an experienced gem cutter could cut around such an imperfection, it's really not that simple. Even expert gem cutters struggle to balance the demands of cutting perfect stones, and situations must be weighed individually.

For instance, if removing the issue that causes the bow-tie effect would shave too much carat weight off of the uncut diamond, a cutter may opt to avoid losing carat value and cut with the issue intact. Or, if there are larger inclusions that could cause more noticeable problems within the uncut gem, a cutter may choose to eliminate those areas at the cost of cutting a stone with a bow-tie. Trying to eliminate a bow-tie can result in cuts that are too deep, shallow, or wide, affecting the gem's overall sparkle.

Identifying the bow-tie effect in diamonds

Here are a few suggestions to spotting the bow-tie effect in your selected gemstone:

Inspect the diamond at a local jeweller

If you're shopping for diamonds in a brick-and-mortar location, make sure you thoroughly examine your gems. Since you can't find information regarding the bow-tie effect in your diamond's grading report, carefully observe your diamond in as many settings as possible while at the store.

Inspect your diamond in different lighting, under a jeweller's loupe, by rotating the diamond, etc. You can also observe the colors of light the stone is emitting to identify obstructions. Flashes of red and green indicate a quality cut, but if you see too much blue light across your diamond's surface you may want to inspect it more closely.

Whatever it takes, make sure you physically appraise the gem, and ask your jeweller questions if you're not sure. Jewellers are typically happy to help, and they can guide you to a set of diamonds that have as little or as much bow-tie effect as you want.

Use the videos and photos provided by retailers online

If you're purchasing your diamond online, take advantage of the revolutionary tools offered to observe diamonds online. Never buy a diamond sight unseen! There are plenty of online retailers that provide full, 360 degrees imaging and videos so you can properly examine your diamond's scintillation.

How to choose diamonds with the bow-tie effect

So how can you make sure you buy the diamond that's right for you, with or without a bow-tie? Here are some recommended tips for purchasing diamonds that may experience the bow-tie effect:

Remember what the bow-tie effect involves

Don't forget that the bow-tie effect is not always a negative feature, but it does mean there is a light blockage within a diamond. Understanding what the bow-tie effect is can help you decide whether the feature is something that will bother you. Also, keep in mind the diamond shapes that typically suffer from the bow-tie effect: pears, hearts, ovals, and marquise.

If you're interested in any of these shapes, it's important to keep the bow-tie effect in mind while shopping.

Balance the bow-tie effect and the 4Cs

While a strong bow-tie effect may seem like a dealbreaker, it's important to consider all of the 4Cs in your diamond buying decisions. The 4Cs are the true markers of a diamond's quality, and they dictate price and value over time. Make sure you understand what you want in a diamond and which qualities matter most to you before focusing on the bow-tie effect.

Diamond buying is a personal decision, as each buyer seeks something different from their chosen gem!

View diamonds from every angle

Find a jeweller that you trust that will allow you to carefully examine any diamonds you are interested in. Try different lighting, positions, and more to get a full view of all of your diamonds' features and identify the intensity of the bow-tie effect in each. If you're buying online, take advantage of video technology to observe every facet of your diamond. Never buy a diamond without seeing it first!

Compare your chosen diamond with other diamonds

Whether buying online or in a store, take some time to compare your diamond to others. Even if you're only interested in one, it can be helpful to see how your chosen stone looks in a lineup of comparable diamonds. Doing so allows you to compare its bow-tie, color, and other factors relative to other gemstones.

The bow-tie effect - a personal choice

As mentioned, the bow-tie effect isn't necessarily a negative characteristic. Many people enjoy the sleek, classy look of the bow-tie within their diamond, and it provides a level of character for those who feel diamonds all tend to look alike. However, avoiding diamonds with large bow-ties that affect sparkle is still recommended!

More On Diamond Brilliance - What Makes Diamonds 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 jewellery. 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 scintillation 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 girdle 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 jewellery. 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 jewellery. 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'

As mentioned, 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.

Final Thoughts

Cut is often consider the most important of the 4Cs 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.

Like the other diamond Cs, 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 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.

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.