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17.1 Colour grading

Colour in the diamond trade usually refers to the amount of yellow in a stone, but can also indicate brown or gray and sometimes all three.

The most treasured diamond colour is actually the "colourless" grade -- one without any colour at all.

Today's standard colour grading scale was first developed by the Gemological Institute of America (GIA). Other colour scales are still used in other parts of the world.

The GIA scale starts with D for perfectly colourless stones, and gives a Z colour grade to diamonds having a noticeable yellow tint, with every letter between indicating the many gradations possible. Most people find colours D through L to be the most attractive, and they are the most rare as well. This means they are also more expensive. Some others prefer the pronounced yellow tints, so their chosen diamond will be much less expensive. Price starts to rise sharply after the colour falls of the Z end into the fancy light yellow colour.

The majority of polished diamonds are graded for their lack of colour.

If one diamond can be shown to have a "better colour", i.e. less colour, than another of the same weight, clarity and cut, then it will have a higher value.

If a stone has a noticeable and attractive colour, it is termed a fancy coloured diamond. Fancy coloured diamonds have their own pricing scale; most are valued for their depth of colour rather than their lack of colour.

Most polished diamonds appear "colourless" and are termed 'white'. The majority of these, however, exhibit just a tint of yellow, even though to the untutored eye they are more or less colourless. The range of yellow tints has been called the 'Cape Series', as colourless to pale yellow diamonds were commonly found in the Cape region of South Africa when this term was first used. Diamonds also occur with tints such as brown, grey or green. We will concentrate on the grading of colourless to near-colourless diamonds.

Diamond Colours

Below are samples of several diamond colours (with variations depending on your monitor). Note the subtle differences among colours as you go down the alphabet from D (perfect, colorless) to Z (the most yellow and least expensive).

 

 

 

 

Most people never imagine that diamonds of other colors, called "fancies," are also available in very limited supply. Diamonds with more color than the Z shown here include fancy yellow, canary yellow, and others. The more expensive and treasured stones have pure tints with very little brown or gray tones to wash the fancy color. Colors such as "intense purplish pink," perhaps the most rare and treasured of fancy diamond colors, might sell for as much as $125,000 per carat for 1-carat stones, wholesale!

Colour Grades

Each colour grade represents a 'spread' or range of colour, not just one point along the colour scales.

The point of division between each colour grade in any colour grading system is an entirely arbitrary point. The continuous colour range is thus divided into selected ranges in order to simplify the assessment of quality. It enables one person to describe a stone to another person using fixed reference points that are familiar to both.

Here is an explanation of each of the color grading sections. They are divided into sections because the colors themselves tend to be valued in these groups. For instance, the D-E-F is considered the colorless grading section, the G-H-I the face white section. And the diamond industry tends to group these grades together with smaller price per carat variables occuring within these sets than between these groups and the groups higher or lower. So it will be important for you to know how these break up, mainly because you may have a client that cannot quite afford a G color diamond, but a nice I color can still give them a face white color while saving them some money. Its just something that helps you make the sale by knowing the small variables that can make the difference in price and quality.

D-E-F

The colors of D-E-F are known as the colorless grades. The color grade of "D" is reserved for larger diamonds whose colors can be more accurately graded due to a larger stone to work with. Diamonds of sizes under .50 carat usually will get a top grade of "F" due to the greater difficulty in grading a small diamond to the exact color grade.

G-H-I

These are known as the "face white" or "face up colorless" grades. Since these diamonds will appear colorless when viewed through the "face up" position or through the table, but when turned upside down for proper grading the stone will show a slight tint of color. This is due to the brilliance of the stone masking this very slight tint when viewed through the table.

J-K-L Much maligned by jewelers and consumers, this grading range can offer some very nice diamonds if they are proportioned properly. A well cut diamond of the K-L colour range will still appear mostly colourless and can save the consumer a good deal of money over a colour grade of a higher range. Again, the cut is the key to keeping the stones of slight tint beautiful.

M-Z

The lower colors from "M" through "Z" will have a continuously increasing amount of yellow tint. Ranging through the off colors and ending at the end of the scale beyond which diamonds are considered to have a fancy yellow color. You should be wary, though, of jewelers offering fancy yellow colored diamonds. Sometimes they grade off color yellows as fancies without a proper gemological evaluation by a recognized gemological laboratory. The term fancy beside any diamond color imparts a higher value and higher price to the stone. So you would not accept the term fancy for any diamond you purchase unless it is accompanied by an origin of color report and a diamond grading report from a recognized gemological lab that identifies the stone as being of natural color origin and truly fancy in color.

Colour Grading

Traditionally, natural daylight has been used to 'colour compare' diamonds. This form of lighting has many drawbacks. For example, the intensity of daylight varies with locality and time of day; this affects the perception of colour in a diamond.

To colour grade a diamond accurately, a commerical diamond light box is used. This light must emit little or no UV light. Stray light from overhead lights and windows affects the illumination of the diamond, so darkened surroundings are preferable.

A diamond is graded whenever possible 'side-on' rather than by looking down into the table of the stone. The brilliance observed through the table of the stone may mask any subtle tints of colour, making colour grading difficult.

A diamond's colour is observed along its greatest width. For instance, for an oval shaped stone this will be down the length of the stone.

The stone must be thoroughly cleaned and placed in a white card or tray, table down.

View from just above the plane of the girdle rather than straight at the girdle of the diamond. Bruted stones have a tendency to appear grey along the girdle; this grey colour has no relation to the body colour of the diamond.

The white card or tray gives a neutral background for the stone, but strongly-coloured walls, ceilings or clothes could distract the eye and reflect into the stone to influence the colour grading.

An accurate colour grade is obtained by comparing the diamond against a series of pre-graded colour comparison stones, known as 'master stones'.

Master Stones
Master stones should each be at a minimum of 0.50ct, have good proportions, be of a yellowish tint, with none, or negligible, fluorescence, have a faceted or polished girdle and contain no coloured, black or otherwise disturbing inclusions.

Two slightly different standard sets are discussed.
GIA master stone set comprises nine master stones. Each master stone represents the top of its grade.
A CIBJO master set comprises of seven master stones. Each master stone represents the bottom of its grade.

For a description of the grading process it is sufficient for us to concentrate on the GIA grading system.
The stones are laid out in a line, each 20mm apart.
The master stone 1 is always laid out on the left.
Any stone with a lower colour than master stone 9 which is a top M is referred to as tinted.

Thus if a stone has a better colour than, for example, master stone 5 but worse than master stone 4, it is graded as a 'H' colour.

It should be noted that to achieve the highest degree of accuracy diamonds must be color graded loose and with the proper equipment. The stones should be upside down to provide the best viewing of the crystal color. And a proper "North Light" source should be employed. And any diamond grade offered on a stone while still in its mounting should be noted as being provisional based on the limitations of grading while the diamond was in the mounting.

WARNING: 
Knowing the 4 Cs is NOT enough to price a diamond accurately.

 

At least 13 factors affect diamond value, including fluorescence, table percentage, symmetry and other crucial details. However, the 4 Cs are a good place to learn the basics.

17.1.1 Fancy colour

The colour palette of diamond is richly varied. It ranges from pink through red, green, blue, yellow, brown and black. The rarest colour occurring in natural diamond is red, followed by green, blue and purple. Colour occurs because of the existence of trace impurities. Brightly coloured diamonds, also known as fancies, are rare and valuable.

The most popular fancy color is the champagne color diamond, which is actually a diamond that shows various intensities of the color brown. And since the GIA grading scale covers tints of yellow and not brown, a new system had to be developed to accommodate this color. This was mainly due to the opening of the Argyle Diamond Mine in Australia that produces so many beautiful brown/champagne colored diamonds. For this purpose the "C" scale was developed, that being the scale to judge the level of intensity of champagne color in a diamond.

Regardless of what anyone tells you, it is extremely difficult to color grade diamonds simply by eyesight alone. The most accurate method is to have a master color grading set with a controlled lighting environment...and most important, a gemologist with a lot of experience in the color grading of diamonds. Some people who handle diamonds everyday, such as diamond dealers, can indeed make a pretty close judgment call on a diamond's color simply by eyesight. But since there are such huge variations in prices based on very minute variations in color grades, you should never take someone's word for a diamond grade unless they have been tested and qualified by a proper gemological institute in the color grading of diamonds. And consumers cannot make this judgment call for color grading...even though I hear a lot of them make the boast that they walked into a jewelry store and could tell a diamond was not graded properly for color. This is just not possible unless the diamond is extremely misgraded. So whether you are selling or buying diamonds, make sure that you have either a proper ability to grade the diamond for yourself, or that the diamond has been graded by an experience and properly equipped gemologist or gemological lab.

It does not take much thought to realize that it is going to be very difficult to overcome the limitations of our computer screens when it comes to determining something as subtle as diamond colour grade variations. Just no way to do it. With that in mind, the practice grading images that you are going to work with have been specially chosen to allow you to best see differences in the diamonds shown. You will not be able to separate a G and H colour on a computer screen. But you can tell a light brown from a yellow, a colorless from a medium yellow, etc… And that is what we have endeavored to provide for you, to get your feet wet regarding diamond color grading.

17.2 Clarity grading

Diamond is crystallised carbon, the diamond crystal growing very slowly in the interior of the earth. There are various phases in the growth of a diamond crystal, and during these phases pressure and temperature can vary causing irregularities, called inclusions. Inclusions may take the form of clouds, cavities, cracks or trapped non-carbon minerals. Inclusions can also have a positive purpose - they serve to identify a particular diamond and are an indication of the natural origin of a stone.

Apart from cracks and fissures, about twenty five different mineral impurities are know as inclusions in diamond, the most common being reddish garnet, brown spinel, green enstantite, black ilmenite and dark graphite.

Two of the most common inclusions are crystals and feathers. Crystals are merely minerals trapped inside the diamond. Feathers are breaks in the diamond. A professional grader must use a binocular microscope that magnifies the diamond ten times to locate these tiny characteristics. Then, evaluating the size, location, number and color of all inclusions and blemishes, a clarity grade is assigned.

Clarity is one of the two best-known factors in diamond pricing, along with colour. While the colour does affect a diamond's appearance, obvious inclusions (often called "flaws") may distract your recipient's eye from a stone's overall beauty. We usually recommend diamonds without inclusions or flaws that are visible to the naked eye. This avoids inadvertent negative feedback from friends and ensures the wonderful, lifelong enjoyment of your diamond.

To achieve this, stay well above the I-1 clarity grade. Clarity grades of SI2 or above are defined as flawless to the naked eye, but SI1 is safer in larger sizes. It's not necessary to go all the way up to IF (internally flawless) to get a beautiful diamond. From SI1 and above, diamonds will appear the same to the naked eye, differing only in the other factors of the 4 Cs: including Carat weight, Color and Cut.

Clarity greatly varies from one diamond to another, and no two are exactly alike. The Gemological Institute of America established standardised clarity grades for the diamond trade which are now used worldwide among dealers to help in trading and valuation. The GIA was the first to name graduations of inclusion in diamond.

The following chart gives an idea how each grade might look under a 10x loupe microscope:

 

Clarity Grades

Below are some simplified definitions of the various clarity grades set by the Gemological Institute of America (GIA). For a comparison with other grading systems used in other countries, go to the clarity comparison chart at the bottom of the page.

FL = Flawless -- no internal or external inclusions of any kind visible under 10x magnification to a trained eye, the most rare and expensive of all clarity grades

IF = Internally Flawless -- no internal inclusions visible under 10x magnification to a trained eye, but there may be some tiny external irregularities in the finish

VVS-1 = Very Very Slightly Included 1 -- usually just one tiny inclusion visible only to a trained eye under 10x magnification; very difficult to locate even by an expert eye

VVS-2 = Very Very Slightly Included 2 -- tiny inclusions visible only to a trained eye under 10x magnification; very difficult to locate by an expert eye

VS-1 = Very Slightly Included 1 -- very small inclusions visible with 10x magnification; slightly difficult to difficult to see under a loupe with a 10 power magnification.

VS-2 = Very Slightly Included 2 -- several very small inclusions visible with 10x magnification; slightly difficult to difficult to see under a loupe with a 10 power magnification.

SI-1 = Slightly Included 1 -- small inclusions visible with 10x magnification

SI-2 = Slightly Included 2 -- several small inclusions visible with 10x magnification

SI-3 = Slightly Included 3 -- inclusions that may be visible to the naked eye for a trained observer

I-1 = Included 1 -- flaws that are visible to the naked eye

I-2 = Included 2 -- many flaws clearly visible to the naked eye that also decrease the brilliance

I-3 = Included 3 -- many flaws clearly visible to the naked eye which decrease the brilliance and compromise the structure of the diamond, making it more easily cracked or chipped

SI3

Outside of the GIA Diamond clarity scale is a grade you may have seen called SI3. The Rap Sheet(Rapaport Diamond Report), a Trade Publication, honours the SI3 grade which is given out by EGL, the European Gemological Laboratory. It is described as a split between the SI2 and I1 clarity grade.

If you really want to *see* what the differences in the Clarity Grades look like under magnification, there is an excellent book by Gary Roskin called Photo Masters for Diamond Grading. It provides photographs and explanations of different Clarity Grades and the inclusions causing them.


17.2.1 Define imperfection
17.2.2 Internal blemish
17.2.3 External blemish
17.2.4 Plotting clarity characteristics
17.3 Cut grading

What Are Design and Craftsmanship, and How Do They Affect the Estimation of a Standard Round Brilliant Diamond's Cut Grade? 


In addition to a diamond’s optical attributes, the GIA Diamond Cut Grading System also takes into consideration its design and craftsmanship. This gives a well-crafted diamond the recognition it deserves while properly identifying the factors that make another diamond’s appearance less than pleasing. Both design and craftsmanship reflect decisions made during the fashioning process.

Design factors include the overall physical shape and proportions of a diamond, and how they affect weight and durability. The GIA Diamond Cut Grading System downgrades diamonds that carry excess weight in extremely thick girdles, steep crowns, or deep pavilions. Diamonds with features that make them vulnerable to damage – such as extremely thin “knife-edge” girdles – also tend to receive lower GIA cut grades.

Craftsmanship takes into account the care taken later in the finishing process. Ratings for polish and symmetry are included in this category.

The first step in any evaluation of design and craftsmanship is to measure the diamond’s average girdle diameter and consider its relationship to the diamond’s weight. Understanding this relationship can help you determine the maximum potential cut grade for a given diamond.

 

To determine diameter, measure from one edge of the diamond directly across to the opposite edge. Illustration by Peter Johnston.

Diamonds are measured in millimeters. For a round brilliant, the process begins with measuring the girdle diameter from one edge directly across to the opposite edge.

1. Measure the diameter in several places.

2. Add the smallest and largest diameters and divide by two to average the numbers.

3. Round your result to the nearest hundredth (0.01) of a millimeter.

Example: If minimum girdle diameter = 3.54 mm and maximum girdle diameter = 3.57 mm, then

Average girdle diameter = (3.54 + 3.57) ÷ 2

= 7.11 ÷ 2

= 3.555, round to 3.56 mm

 

What is the American Ideal Cut?

Question:

What exactly is the American Ideal? Was it Americans who refined the cutting/proportioning process?

The American Ideal Cut

Ideal is defined as:

"A standard of perfection, beauty, or excellence."

The standard of perfection and beauty in diamond cutting is embodied in the round brilliant, American Ideal cut. This concept of an ideal cut for diamonds was adopted, refined, and championed by both the GIA and the AGS for over half a century. Both organizations credited the Belgian diamond cutter and mathematician Marcel Tolkowsky (1899-1991) with the key design proportions of the American Ideal, (average pavilion and crown main angles of 40.75 and 34.5 degrees).

"THE QUEST FOR THE IDEAL" 
The GIA diamond course from 1993, on the page titled "The Quest for the Ideal" points out: "Although Diamond Design was first published in England, Tolkowsky's design is often called the American Ideal Cut, because US cutters were the first to adopt it. ... For years, GIA used the American Ideal Cut as the basis of a comparison system in teaching diamond cut evaluation."

Tolkowsky wrote of a breed of diamond cutter whose goal was to cut a diamond "regardless of loss of weight, the only aim being to obtain the liveliest fire and the greatest brilliancy."

Although not the first person to formulate proportions believed to result in maximal brilliance and fire, he is the one most people think of as the father of this ideal.

Tolkowsky's findings became the basis for the American Ideal Cut. And his model for the best-performing round-brilliant diamond remains the most influential in history.

Tolkowsky never called his diamond an "ideal cut." He called it a "high-class brilliant," meaning it had, in his words, "magnificent brilliancy and fire." What's more, he never said he invented his model for the round-brilliant diamond. His "Diamond Design" publication added mathematical support for the rightness of a model already in use. Its origin, he said, lies with others, including an almost forgotten mid-19th century Boston cutter named Henry Morse.

The beginnings of what came to be the American Ideal Cut diamond are traced to Henry Morse, who, in 1860, opened a diamond-cutting firm in Boston, Massachusetts. By 1880 he was recutting the traditional Old European cut diamond without regard for weight retention to produce the most beautiful round brilliant cut diamond of his time. (Morse's model had a pavilion angle within a degree of 41 and a crown angle close to 35 degrees).

His work went largely unheralded because the great majority of diamond manufacturing in the US steadfastly followed traditional European cutting with the goal of maximum weight retention from the rough diamond crystal.

Since the times of Morse and Tolkowsky, cutters of the American Ideal have continued to improve its beauty by lengthening the lower-girdle facets and slightly increasing the table size--all the while staying close to Tolkowsky's and Morse's recommended average pavilion and crown angles (40.75,41 and 34.5,35).

During the 80's, diamond cutters in Japan improved the physical and optical symmetry of the American Ideal cut using instruments that displayed the three-dimensional optical performance of all 57 facets of the round brilliant. The result was a new dimension in cutting perfection that today is called 'optical symmetry'.

Introduced in America in the 90's, the optically symmetrical, 'super ideal' was championed by several American diamond importers and cutting houses. The American Ideal continued to be refined by cutters using the latest diamond cutting technology and optical performance assessment tools.

The American Ideal cut diamond has evolved and improved in optical performance and beauty through the advancing skills and technology of the very best of the diamond cutting profession. Today, cutting firms worldwide are embracing the evolved American Ideal.

Begun in America with Henry Morse, championed by GIA and AGS, and nurtured by American cutters, this pinnacle of performance and beauty represents, in diamond cutting, the culmination of the quest for Ideal.

Photograph of an American Ideal, round brilliant cut diamond shown from a viewing angle of 40 degrees at six different magnifications, 2.5X-10X. This photo displays the American Ideal's potential for fire in high contrast illumination. Fire is the term for the reflections of light dispersed by the diamond into rainbow colors.

DIAMOND BEAUTY - BRILLIANCE, FIRE AND SPARKLE


Fire is an important and desirable aspect of diamond beauty. It is a property of the American Ideal that often goes unheralded, because the bright lighting in today's jewelry stores usually emphasizes the other two aspects of diamond beauty--- brilliance and sparkle. 

The diamond's fire is better observed in high contrast lighting that is less intense. Lighting of this nature may be found in some restaurants, theatres, ballrooms, etc., where the illumination is mainly from spot lighting in otherwise low light surroundings. The prevalence of artificial lighting of this type from gas and kerosene lamps, candles, chandeliers, etc. better highlighted the fire aspect of the diamond's beauty in times prior to the advent of modern, 20th century lighting.

The Official Grades of Cut
Cut grade standards are defined by the GIA in the following terms:
Excellent (Xc), Very Good (Vg), Good (G), Medium (M), and Poor (P). The proportion is graded separately to the polish, proportion coming first. So for example an Xc Vg grade refers to a diamond that is Excellent Proportion with Very Good Polish.
The Effect of Cut on Price

A poorly cut diamond is typically 30% cheaper than an ideal cut diamond, where all other quality characteristics are the same.

GIA bases their new (as of Jan. 2006) cut grade on a combination of face-up appearance, design and craftsmanship elements that all contribute to the diamond's fire and brilliance. They employ a predictive computer model,       
GIA cut grading criteria
Face-Up Appearance     Design     Craftsmanship

Brightness                     Weight Ratio     Polish
Fire                                 Durability     Symmetry
Scintillation            

based on over 70,000 individual diamond observations and 38.5 million proportion sets, to determine a diamond's brilliance based on its interrelated measurements. Most GIA diamonds graded prior to January 1st, 2006 will not have a laboratory-assigned cut grade. The GIA cut grade system includes ratings of Excellent, Very Good, Good, Fair and Poor. GIA does not assign an Ideal cut and an Excellent rating is their highest grade. For comparison purposes, a GIA Excellent cut will be listed as a Blue Nile Ideal cut on our Web site. The cut grades are equivalent. Learn more about the GIA Diamond Grading Report and Diamond Dossier®.

How Does Total Depth Percentage Affect the Estimation of a Diamond's Cut Grade? 


 

Total depth percentage is an important indicator of a stone's overall proportions. It can help you recognize an underweight or overweight diamond. Illustration by Peter Johnston.

The total depth percentage of a round brilliant diamond is its table-to-culet depth, expressed as a percentage of its average girdle diameter. Total depth percentage is an aspect of design, and therefore important to the assessment of an overall cut grade. The total depth percentage and the diamond’s potential cut grade can be determined by following the procedure below.

1. Calculate the diamond’s average girdle diameter.

2. Measure the diamond from table to culet.

3. Divide the depth in millimeters by the average girdle diameter, and multiply by 100.

4. Round the result to the nearest tenth of a percent.

5. Use the table below to help estimate the diamond’s potential cut grade.

Example: A round brilliant-cut diamond has an average girdle diameter of 4.55 mm. Its depth from table to culet measures 2.55 mm.

Divide the diamond’s depth by its average girdle diameter: (2.55 ÷ 4.55) = 0.5604

Multiply by 100: 0.5604 × 100 = 56.04%

Round to nearest tenth of a percent = 56.0%

Total depth percentage is useful in determining why a diamond is underweight or overweight in relation to its diameter. Well-proportioned diamonds typically have total depth percentages around 60.0 percent.

Diamonds with total depth percentages below 55.0 percent are generally underweight, with shallow crowns, shallow pavilions, or a combination of both. They might also have large tables or very thin to extremely thin girdles.

Diamonds with total depth percentages of 65.0 percent or more are generally overweight, with steep crown angles, deep pavilions, or both. Excess weight is often located at the girdle, which might range from thick to extremely thick. Some stones might have large tables, shallow crowns, and exceptionally deep pavilions. Others might combine slightly steep crowns with moderately thick girdles and moderately steep pavilions.

It’s important to understand that while a total depth percentage of 60.0 percent suggests good proportions in a diamond, it doesn’t guarantee them. A diamond with a 60.0 total depth percentage might still have negatives like a shallow crown, a very thick girdle, or a deep pavilion.

As you can see from this chart, some total depth percentage (TDP) ranges overlap between grades. For example, a diamond with a total depth percentage of 60.0 percent can fall within any of the GIA cut grades. A total depth percentage of 52.0 percent, however, falls outside the ranges for Excellent, Very Good, and Good and can result in only a Fair or Poor grade. When a diamond’s total depth percentage falls outside any of the top ranges, it can never achieve one of the better cut grades.

Possible Cut Grade(s)

TDP Range

TDP Comments

<51.0%

Extremely shallow crown and/or pavilion, thin girdle

F, P

51.0% to 52.9%

Very shallow crown and/or pavilion, thin girdle

G,F, P

53.0% to 55.9%

Shallow crown and/or pavilion

VG, G, F, P

56.0% to 57.4%

Moderately shallow crown and/or pavilion

EX, VG, G, F, P

57.5% to 63.0%

Generally standard crown, pavilion, and girdle

VG, G, F, P

63.1% to 64.5%

Moderately steep crown and/or pavilion

G, F, P

64.6% to 66.5%

Steep crown and/or pavilion

F, P

66.6% to 70.9%

Very steep crown and/or pavilion, thick girdle

P

>70.9%

Extremely steep crown and/or pavilion, thick girdle

 

Diamond Cut: The Shape

CUT of a diamond pertains both to the shape (round, marquise, princess, etc.), and to the make (how well it is cut for proportion and finish). These are the only factors in diamond grading that are controlled by human hands.

First we will talk about the eight major diamond shapes, your first decision when shopping for a diamond. On the next page we will describe a few details about the make of a diamond.

Diamond Shapes

 

 


The first step in choosing a diamond often involves selecting your favorite (or her favorite) shape. The Round Brilliant is by far the most popular shape, and it is the most readily available in every possible quality and size.

Contrary to popular belief and perhaps your experience in most stores, fancy-shaped diamonds (as all non-round diamonds are called) are often less expensive than their round brethren... at the wholesale level.

The Princess cut is becoming popular because it is both brilliant and unique. The Princess shape actually saves money for a cutter, since it is closest to the octahedral "habit" of rough diamond crystal, the most common formation of diamond in the rough. (The octahedron is like two pyramids base to base.)

Compared to a Round Brilliant, a cutter can retain more of the original crystal when cutting an octahedron into a Princess shape. The square corners of the rough need to be cut away to create a Round, but they are saved when cutting a Princess.

The more he saves of his original rough crystal, the less the cutter loses on his financial investment in the stone, and therefore you pay less as well.

But many shapes can be beautiful if they are cut well, including the Marquise, Oval, Pear, Radiant, Heart, Emerald and other major shapes. But all fancy shapes have an inherent difference in the physics of light. The longer shapes have a slight "bow tie" effect. This means they have a small zone in the center where light leaks out the bottom, creating a darker area in the shape of a bow tie. This is especially true for the Pear, Oval, Marquise, and Heart shapes.

For ideal proportions that maximize brilliance, fire and sparkle, you can't beat the new Round Brilliant Ideal Cut. The science of cutting a diamond to bring out the full potential of its beauty has developed significantly in the past 10 years. Many diamond cutters now specialize in creating ideal proportions, and such stones have become quite popular. Ideal Cut diamonds command a slight premium because of 1) the extra care and skill needed during cutting, 2) more of the rough is usually cut away, and 3) they are scarce and in high demand.

How to Determine if a Standard Round Brilliant Diamond Is Overweight When Estimating Its Cut Grade?

 

A standard, one-carat round brilliant diamond typically has an average girdle diameter of 6.50 mm. Diamonds with this diameter that weigh significantly more than one carat, or that weigh one carat but look significantly smaller than 6.50 mm when viewed face-up, are described as “thick” or “heavy” in the trade. These diamonds generally have much more total depth than a well-proportioned diamond should. In other words, they have “hidden weight” and are considered by GIA to be “overweight.”

When a diamond is overweight, it’s heavier than its average girdle diameter might suggest. You can find out if a diamond is overweight by determining its diameter and its carat weight, then comparing the weight to that of a reference diamond with fairly standard proportions.

 



These diamonds have the same girdle diameters, and they would probably appear to be the same size face-up, but their profiles show very different girdle thicknesses. A thicker girdle (right) is often used to add weight to a fashioned diamond. Photos by Don Mengason.

 

1. Weigh the diamond and round its weight to the nearest 0.01 ct.

2. Refer to the Diamond Weight Chart to find the estimated weight for a diamond of standard proportions that has the same average girdle diameter as the diamond you are evaluating.

3. Compare the weights. If your diamond weighs more than the example in the chart, calculate the percentage difference between its actual weight and the weight “suggested” by its diameter. To calculate this percentage, take the difference between the diamond’s suggested weight and its actual weight, divide that amount by its suggested weight, then multiply by 100.

For example, according to the Diamond Weight Chart, a diamond with a diameter of 4.02 mm should weigh about 0.24 ct. Your sample diamond’s actual weight is 0.27 ct.

First, subtract the suggested weight from the actual weight.

0.27 − 0.24 = 0.03

Then divide the result by the suggested weight.

0.03 ÷ 0.24 = 0.125

Next, multiply by 100.

0.125  × 100 = 12.5%

Finally, round to the nearest whole percent = 13%

The result tells you this stone is about 13 percent heavier than its diameter suggests. On this basis, the highest cut grade it could receive is Very Good, according to the chart below. Keep in mind that all other factors must be considered to determine if it might receive a lower cut grade.

Diamond Cut Grades and Overweight Percentage

Possible Cut Grade(s)   Percent Overweight

E, VG, G, F, P                <8%

VG, G, F, P                    8% to 16%

G, F, P                            17% to 25%

F, P                                 >25%

You can determine why a diamond is overweight by analyzing its crown height, pavilion depth, and total depth percentage. You should also consider girdle thickness because it is easy to hide weight in an extra-thick girdle.

How to Visually Estimate Fire in a Standard Round Brilliant Diamond?

 

 

Strong, concentrated spot lighting will make fire more visible. After you have estimated the brightness and pattern of a diamond, leave it in the tray and switch off the diffused fluorescent light source. Use another spot light source such as an LED flashlight. Tilt the tray to observe the diamond at different angles and make a visual assessment of its fire. Note that observation and evaluation of fire are best done in a slightly darkened room.

In practice, if all other factors are equal, it is more difficult to evaluate differences in fire in stones smaller than a half carat.

Use the following fire-rating guidelines to assign a grade for fire, from Excellent to Poor:

  • Excellent: Numerous bright flashes of fire across most of the crown facets and table.
  • Very Good: Flashes of fire across many of the crown facets and table.
  • Good: Some flashes of fire.
  • Fair: Small flashes of fire, which might be confined to small areas of the diamond’s crown.
  • Poor: Very few small flashes of fire, which might be confined to very small areas of the diamond’s crown.




These diamonds display Very Good (left), Fair (middle), and Poor (right) fire. Photos by Eric Welch.

Review your visual estimates for brightness, fire, and pattern. The lowest estimate sets the diamond’s estimated visual cut grade. For example, if you estimated the diamond’s brightness as Very Good and its fire as Very Good, but there was a distracting pattern that only rated Good, your visual cut grade estimate is Good.

How to Visually Estimate the Brightness of a Diamond?

 

 

A standardized viewing environment, including controlled lighting and a neutral background, is essential for making consistent comparisons between diamonds. Diamond appearance is very sensitive to changes in lighting conditions, so the same diamond can look quite different when viewed under different types of lighting in different positions. Since diamonds also reflect everything around them, even a grader’s clothing or nearby furniture, it is always best to have a neutral, “uncluttered” environment within which to perform observations.

A mixture of diffuse and “spot” lighting is very helpful for assessing face-up appearance (which includes brightness, fire, and pattern). Fluorescent lighting from an overhead or desk lamp can help evaluate a diamond’s brightness and pattern, but the same light also suppresses its fire. Spot lighting (also known as “point source” lighting) emphasizes a diamond’s fire, but if the lighting is too strong, it can overwhelm everything else and make the diamond appear dark.

The GIA DiamondDock™ provides consistent and repeatable viewing conditions for every diamond cut assessment. It features daylight-equivalent fluorescent light for judging brightness and pattern, as well as an array of light-emitting diodes (LEDs) for judging fire, all housed within neutral gray walls.

However, the DiamondDock™ is not a requirement for discerning differences in diamond appearance. Most diffused light environments that have white-colored ceilings and walls can be used with almost the same results. A standard color-grading box like the Macbeth Judge II, or a common fluorescent desk lamp with D65 fluorescent tubes used in a neutral environment, is a useful alternative for assessing brightness and pattern.

It is also beneficial to use a neutral gray tray to hold the diamonds while observing them. A white background might make a diamond look brighter by hiding or masking areas of light leakage. A black background reveals possible areas of light leakage, but can overemphasize them and make the diamond look too dark. The gray color allows you to see potential areas of light leakage without overemphasizing them.

The following steps outline the procedure for estimating a round brilliant diamond’s brightness using the GIA DiamondDock™ or an equivalent standardized environment.

1. Clean the diamond with a gem cloth.

2. Place the diamond face-up in the gray tray and place the tray in the DiamondDock™ (keeping it near the bottom center of the viewing booth) or a comparable lighting environment. Make sure you’re in a comfortable position and at an optimal viewing distance, usually 12 to 18 inches from the diamond. Turn on only the diffused fluorescent light. Tilt the tray as necessary to observe the diamond at different angles and make a visual assessment of its overall brightness. Remember that you are only assessing the total amount of white light that is returned, not whether that light is in a pleasing pattern. Use the following brightness-rating guidelines:

  • Excellent – Diamond appears very bright. There are very few dark areas, and these are evenly distributed across the diamond’s crown. The area directly below the table facet, especially around the culet, remains bright.
  • Very Good – The diamond appears bright. There are a few dark areas, but the area directly below the table facet remains bright.
  • Good –The diamond has some life, though dark areas detract from its appearance. The upper girdle facets, the area under the diamond’s crown around the culet, or both, might be slightly to moderately dark.
  • Fair –The diamond has little life. Some crown areas are bright, but large areas are gray. There might be concentrated areas of darkness within the table area, around the girdle, or both.
  • Poor –The diamond appears dull and lifeless. Only small areas of the crown are bright. The table area might be very dark, with the dark area extending beyond the table into the surrounding crown facets. The upper girdle facets might be very dark and distracting.

3. Assign a grade for brightness, from Excellent to Poor.

 

17.3.1 Common cutting faults
17.3.2 Centre and off centre sawing of diamond octahedral
17.3.3 Steps to evaluate proportions and methods by which determinations can be accomplished
17.3.4 Estimate table size and girdle thickness
17.3.5 Table size and relative depth affect weight and why these and girdle thickness show relative weight retention
17.3.6 Polish, symmetry
17.3.7 Quality of girdle surface
17.3.8 Culet size etc
17.4 Grading fancy shaped diamonds
17.5 Grading fancy coloured diamonds
17.6 Grading mounted diamonds


Clarity Grading Scales
(for diamonds 0.46 carats and above)
GIA AGS CIBJO
IDC
SCAN.D.N.
F
Flawless
0 F
Flawless
LC
Loupe Clean
IF
Internally Flawless
1 IF IF
VVS1
Very Very Slightly Included 1
VVS1 VVS1
VVS2
Very Very Slightly Included 2
2 VVS2 VVS2
VS1
Very Slightly Included 1
3 VS1 VS1
VS2
Very Slightly Included 2
4 VS2 VS2
SI1
Slightly Included 1
5 SI1 SI1
SI2
Slightly Included 2
6 SI2 SI2
SI3
Slightly Included 3
I1
Included 1
7-8 P1
Pique 1
P1
Pique 1
I2
Included 2
8-9 P2
Pique 2
P2
Pique 2
I3
Included 3
9-10 P3
Pique 3
P3
Pique 3

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The Geohavens name is an assurance of timeless beauty, distinct quality and uncompromising value. The Company spares no effort in sourcing from the farthest markets and the deepest mines in order to unearth the most attractive gems.

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