Diamond Anatomy and Shapes

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AESERA  Jewellery DESIGNING ACADEMY

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seshu.gopal@jewelrydesignacademy.com

 HERE ARE THREE BASIC PARTS TO EVERY CUT DIAMOND:

The crown (top)

The girdle (around the middle)

The pavilion (the bottom).

CROWN The crown consists of a large flat area on top called the table, and a number of facets. As the diamond catches the light, the job of the crown is to split the light entering the diamond into white light, which gives the stone its brilliance, and colored light, which gives it fire, or dispersion.

GIRDLE The girdle is the thin, unpolished band around the widest part of the diamond. The function of the girdle is to protect the edge of the stone from chipping (even though diamond is the hardest natural substance on earth, it can be chipped )

PAVILION The pavilion has the most important job, which is to reflect the light that passes through the crown back into your eyes. Think of it as a cone lined with mirrors. The light enters the diamond through the crown, splits into white and colored light, bounces off the facets of the pavilion back up through the crown, where you see it as sparkle! But to achieve the maximum sparkle — that magic combination of brilliance and fire — the diamond must be well cut and cut in the proper proportions.

THE SIZE OF THE TABLE, THE SYMMETRY OF THE FACETS, THE THICKNESS OF THE GIRDLE, AND THE ANGLE OF THE PAVILION MUST ALL WORK TOGETHER TO GIVE THE DIAMOND THE SPARKLE YOU WANT.

TABLE The size of the table, as a percentage of the crown, is important because it determines the amount of brilliance, or white light, the diamond will reflect. For example, if the table is 60% of the diameter of the crown, 60% of the light you see will be brilliance and 40% will be fire, or dispersion. Avoid a diamond with a table area of 65% or higher. It will give the diamond too much brilliance, and not enough fire–and the diamond will look fuzzy or foggy. (The only exception to this rule is emerald and rectangular cut diamonds that can have a 65% table. This includes all princess cuts, quadrillions and radiants.) HERE’S THE FORMULA: Table area 53-60% = GREAT! Table area 61-64% = GOOD! Table area 65%+ = except emerald and rectangular cuts.

FACETS The typical diamond is cut with 58 facets, 33 on the crown and 25 on the pavilion. On a well-proportioned stone, these facets will be uniform and symmetrical. If they are not, the diamond’s ability to refract and reflect light will suffer. Furthermore, a poorly-cut diamond just won’t look right to the eye. The sad fact is, 75% of all rounds and 88% of all other shapes on the market are poorly proportioned! Poorly proportioned stones are more profitable for the dealer, because they retain more of the weight of the rough or uncut diamond.

GIRDLE You don’t want a diamond with a girdle that’s too thin, or one that’s too thick — you want one that’s just right! The whole purpose of the girdle is to protect the edge of the stone from chipping. A girdle that’s too thin doesn’t give enough protection. A girdle that’s too thick does protect against chipping, but it doesn’t look so good. So you want a diamond with a medium girdle, neither too thin nor too thick. How do you tell? Look at the diamond from the side. If it looks like there’s a white chalk line around the middle of the stone, the girdle is too thick. If you don’t see any girdle at all with the naked eye, look at the same area of the stone with a 10X loupe. If you can’t see a girdle with the loupe, it’s too thin.

PAVILION The job of the pavilion is most important of all: to reflect light. The light enters the diamond through the table and the facets of the crown, passes through the diamond, and is reflected back by the facets of the pavilion. Here’s the important part: The angle of the pavilion for a round diamond must be between 40-41.5 degrees. 40.75 degrees is perfect. For marquise, pear, and ovals, the perfect angle perfect angle is 40 degrees, but an acceptable range is 39.25–40.75 degrees. For emerald and rectangular cuts, perfect is 45.05 and an acceptable range is 43.3-46.8 degrees. If the pavilion angle is not exactly right it will not reflect the light properly, and the diamond won’t have the sparkle it should. In a round diamond, there’s a dramatic loss of sparkle if the angle is even a tenth of a degree above 41.5 or below 40 degrees. In marquise, pear, or oval, maximum sparkle is achieved with a 40 degree pavilion angle, but the angle can be increased or decreased by as much as three-fourths of a degree with only a 10% loss of sparkle. Emerald and rectangular cut diamonds have the widest allowable variance of 1.75 degrees. Each extreme will also cause a 10 percent loss of sparkle.

CROWN ANGLE The angle of the crown is also important, but it doesn’t have to be quite as precise as the pavilion angle. The angle of the crown should be 32-35 degrees. If it’s smaller than 32 degrees, the diamond is what we call spread-cut. This makes the table area too large and the girdle too thin, and we already know what problems that causes. If the angle of the crown is above 35 degrees, it makes the diamond “top heavy.” This results in a smaller diameter, making the diamond look smaller than it really is. The last thing you want is a one-carat diamond that looks like a 3/4 carat!

CULET Finally, at the very bottom of the diamond–the base of the pavilion–there may be a small facet called the culet. If this facet is too large, when you look straight down through the table it will look like the diamond has a hole in the middle. Make sure the stone has no culet or a very small culet.

TWO OTHER IMPORTANT DIAMOND MEASUREMENTS Two other measurements to consider are: total depth and length-to-width ratio.

TOTAL DEPTH is a simple, straightforward measurement: take the height of the stone and divide it by the diameter of the stone. For a fancy stone, the diameter is measured at its widest part. The answer should be in the 56%-61% range. If it’s not, it means there’s something wrong with the crown angle and/or the pavilion                angle, or the girdle thickness. (The only exception to this rule is emerald or rectangular cut diamonds that can have a total depth of 65%.)

THE LENGTH-TO-WIDTH RATIO is used to determine if a fancy-shaped diamond (anything other than round) is well-proportioned. For example, we don’t want to buy a marquise that is so skinny it looks like a banana, or one that’s so fat it looks like a football. Pleasing proportions aside, the length-to-width ratio also affects a phenomenon known as the bow-tie. Let me explain.

Fancy shapes are not symmetrical —  only a round is. And because fancy stones aren’t symmetrical, they all have a bow-tie — two triangular shadows in the middle of the diamond where light leaks out the bottom. If the length-to-width ratio is off, it will intensify the bow-tie in the stone! For a marquise diamond, the length should be no less than 1.75 times the width, and no more than 2 times the width. For pear shapes, the length should be no less than 1.5 times the width, and no more than 1.75 times the width. For emerald and oval shapes, the length should be no less than approximately 1.3 times the width, and no more than 1.75 times the width.

PROPORTIONS MADE EASY GIA has made it easier to determine if a diamond is well-proportioned by dividing all cut diamonds into four classes. Essentially, Class One and Class Two diamonds are well-proportioned; Class Three and Class Four diamonds are not. Class One diamonds are investment-quality stones, beautifully proportioned and priced to match. If your objective is to buy a beautiful diamond to wear,                  Class Two is fine.

 ADVICE: Don’t go below Class Two. And if the jeweler doesn’t know what the GIA classes are, move on!

PROPORTION AND PRICE A poorly proportioned diamond is worth as much as 40% less than a well proportioned stone. One reason for the difference in worth is that it takes a 3-carat rough, which is a diamond as it’s found in nature, to produce a well proportioned 1-carat cut stone. But it only takes a 2-carat rough to produce a poorly proportioned 1-carat stone. A poorly proportioned diamond will not sparkle nearly as much as a well proportioned diamond. If a diamond is poorly proportioned, only 35-40% of the light that enters it will reflect back up into your True Love’s eyes, while a well proportioned diamond will reflect close to 90% of the light. A woman wants a diamond to be “big, clean, white and sparkly,” and it won’t sparkle unless it’s well proportioned.

Diamond Shapes

Finding the perfect shape for your diamond is an important consideration. The cut must be perfect and should not be poorly proportioned. A poorly proportioned diamond or “Off Make” will never have the maximum sparkle, fire, or brilliance that it would achieve if it were properly cut. The chart with photos below shows excellent examples of well proportioned diamonds.

Diamonds come in a variety of shapes. Do not confuse cut with shape. Cut is what determines how well-cut your diamond is, where as diamond shape is the shape it was cut into.

ROUND BRILLIANT
Do not confuse with Round. The Round Brilliant is the modern version of the Round which has been refined for maximum shine. The Round Brilliant is by far the most popular and has the best angles to shine maximum brilliance.

ASSCHER
A square cut similar to an emerald with step facets; however, it is more square rather then rectangular shaped. Like the emerald, it has clipped corners. Recently the Asscher shape has become very popular.

EMERALD
A more traditional shape, the Emerald is not as popular as it once was, but still retains its old world elegance..

RADIANT
Popular before the Princess shape was around, the Radiant has more facets than a Princess, but has the corners trimmed like the Emerald shape. This shape is not widely popular.

HEART
Hard to find due to low demand, but some people prefer a Heart shape diamond for sentimental purposes.

MARQUISE
Like the Emerald, the Marquise is a traditional shape. This is probably the fourth most popular shape behind the Round, Princess and Oval..

PEAR
Mostly used in pendants, the Pear shape diamond is shaped in a tear drop shape and has fairly good proportions to refract light well.

IDEAL CUT OF DIAMOND

Everyone has their own opinion on what Ideal is. Some people prefer a diamond to have a somewhat larger table, say around 60%, so the diamond “looks” bigger. Some want the Tolkowsky Ideal Cut, as calculated in the early 20th century by mathematician Markov Tolkowsky. The diagram below describes the Class 1 and 2 grades of GIA. They are the largest body in the world for diamond grading, and we use their classifications to grade our diamonds. Class 1 is Ideal. Class 2 is Very Fine, Class 3 is Fair, and Class 4 is Poor. GIA’s definition of “Ideal – Very Fine” Class are as follows:

Please keep in mind that diamonds other than Round Brilliant do not always have their cuts measured in such detail because they are classified as “fancy cut” diamonds and have very loose tolerances.

When buying a diamond, especially a Round Brilliant cut diamond, it is always best to have a complete analysis of cut. This will tell you all the specifications of the diamond’s cut such as table percentage, depth percentage, etc., usually obtained from a scope (or megascope).

BASIC 4 C’s OF DIAMOND

CARAT
Carat weight is the weight of the diamond measured in carats. One carat is divided into 100 “points,” so that a diamond of 75 points weighs 0.75 carats. Carat weight is the most obvious factor in determining the value of a diamond. But two diamonds of equal carat weights can have very different prices, depending on their quality. Diamonds of high quality can be found in all size ranges.

The scale above depicts the carat weights and diameter sizes of round diamonds. Other diamond shapes will vary. For example, while a 1 carat round shape diamond is 6.5mm on average, a 1 carat princess shape diamond is often 5.5mm instead.

Since diamonds are measured by carat weight, and not size, two diamonds of the same weight could have different sizes. Why? If a diamond is cut too shallow it will have a larger diameter but a smaller depth. Likewise, if a diamond is cut too deep (or bottom heavy) it will have a smaller diameter and thus appear smaller when viewed from the top.

Cut is very important. A properly cut diamond will both yield a good face up size and sparkle well. For example, let’s say you’re interested in a 1.00ct round diamond. A poorly cut diamond that is bottom heavy may only have a diameter of say 6.1mm. So not only are you short changed on the face up size, but you get a diamond that was not cut to it’s full potential and thus does not sparkle like it should.

This is why it’s important not just to get the biggest diamond you can afford, but the best cut diamond as well.

CLARITY
Diamond Clarity is a measure of a diamond’s internal flaws and impurities. A diamond that is virtually free of interior or exterior inclusions (commonly referred to as flaws) is of the highest quality, for nothing interferes with the passage of light through the diamond. To determine a diamond’s clarity, it is viewed under 10x magnification by a trained gemologist. Small inclusions neither mar its beauty nor endanger its durability.

Flawless - No internal or external flaws.
Internally Flawless – No internal flaws. Very rare and beautiful diamonds which are quite expensive.
VVS1, VVS2 - Very, Very Slightly Included: Very difficult to see inclusions under 10x magnification. An excellent quality diamond.
VS1, VS2 – Very Slightly Included: Inclusions are typically not visible to the unaided eye. Less expensive than the VVS1 or VVS2 grades. Even properly graded VS2 diamonds can have visible inclusions in very large sizes or diamonds that do not have many facets which make flaws more visible such as an emerald shape.
SI1, SI2 - Slightly Included: Inclusions are typically visible under 10x magnification, SI clarity diamonds are usually of the best value since inclusions are not always visible to the naked eye and prices are reasonable when compared to prices of the VS2 clarity and up grades. Some SI clarity diamonds do have visible inclusions and should be evaluated carefully.
SI3 - Slightly Included-Included: SI3 is an EGL grade and is not recognized by GIA or other gemological institutions. The SI3 clarity grade has been adopted by other labs as well. Typically an SI3 clarity grade would usually be given an I1 grade by the GIA.
I1 - Included: an I1 clarity diamond will have a visible flaw which can be seen with the naked eye, but there should only be one major flaw which is not too obvious. Overall the diamond should still look nice however I1 clarity grades vary quite a bit so one should be very careful when making a selection. If your budget only allows for an SI3 or I1 clarity diamond, be sure to examine it thoroughly before purchasing and make sure the inclusions do not detract from the overall beauty of the diamond.
I2, I3 - Included: These diamonds will have inclusions visible to the naked eye, and will have many black spots from the black inclusions and/or appear very cloudy or milky from the white inclusions, feathers and cracks.

COLOUR
The diamond color grading scale varies from totally colorless to light yellow. The differences between one diamond color grade and another are very subtle and difficult to distinguish.

D-F : Colorless: perfect or almost perfect color.
G-J : Near colorless: good to very good color, and this diamond may “face up” colorless when mounted, especially in white gold or platinum.
K-M : Light but noticeable yellow or brown tint. Not recommended for larger diamond stone purchases, especially in engagement rings.

Out of the 4 C’s, color and cut are the two most important characteristics of a diamond. Do not compromise on color. An “H” color or better is usually best.

CUT
Many people confuse diamond cut with the shape of a diamond. Unlike shape, diamond cut is the metric used to evaluate the precision and quality of the overall cutting itself. Diamond cut is the most complex of the 4 Cs, and not even the major labs agree on how to best measure the quality of a diamond’s cut. Diamond Cut usually takes into consideration 3 criteria: Proportions, Symmetry and Polish. Sometimes Light Performance or other tests can be used to also calculate the precision of the diamond cut.

1. When a diamond is cut to proper proportions, light is reflected from one facet to another
and then dispersed through the top of the stone similar to the image shown to the left.

2. If the cut of the diamond is too deep, some light escapes through the opposite side of the pavilion.

3. If the cut is too shallow, light escapes through the pavilion before it can be reflected.

Up until several years ago, evaluating the cut of a diamond was not an easy task. Dimensions and proportions of the diamond as well as its finish (both symmetry and polish) were all the information able to be evaluated, thereby making it difficult for consumers to understand what is a well-cut diamond and what is not.

Symmetry measures how well the facets match the other facets. A diamond cut with very good or excellent symmetry means that if you were to look at all the facets and compare to one another, they would look very uniform with very little variance. This doesn’t mean however the diamond is not cut too deep or too shallow.

Polish is a measure of the surface finish. If a diamond is only polished “Fair” or “Good” it does not allow maximum transition of light through the facets, due to it’s “rough” surface texture. Very Good polish by most lab standards is usually sufficient to get the top cut grade, and excellent/ideal is often preferred. Polish graded above Very Good is not detectible to the naked eye.

So while symmetry and polish help you determine if the diamond is cut well, it doesn’t always mean the diamond will perform like a well cut diamond.

Recently both the GIA and AGS have adopted “Cut Grades” which factor all these things together; the proportions, symmetry and polish, and sometimes even light performance. Currently, GIA issues a cut grade on its round diamonds, and AGS issues a cut grade on round and princess shape diamonds they grade.