HomeDiamond Grading 1: Colour Grading

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 and guidelines was first developed by the Gemological Institute of America (GIA). The colour of graded diamonds is compared to the colour of control stones, preselected gems of a specific colour. 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, colourless) to Z (the most yellow and least expensive).

 

Most people never imagine that diamonds of other colours, called "fancies," are also available in very limited supply. Diamonds with more colour 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 colour. colours such as "intense purplish pink," perhaps the most rare and treasured of fancy diamond colours, 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 colour grading sections. They are divided into sections because the colours themselves tend to be valued in these groups. For instance, the D-E-F is considered the colourless 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 colour diamond, but a nice I colour can still give them a face white colour 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 (Colourless)

The colours of D-E-F are known as the colourless grades. The colour grade of "D" is reserved for larger diamonds whose colours 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 colour grade.

G-H-I (Face white)

These are known as the "face white" or "face-up colourless" grades. Since these diamonds will appear colourless 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 colour. This is due to the brilliance of the stone masking this very slight tint when viewed through the table.

J-K-L (Faintly tinted)

Much maligned by jewellers 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 colours from "M" through "Z" will have a continuously increasing amount of yellow tint. Tinted, usually yellow, may progress to brownish. Tint visible to the naked eye, even when mounted. Ranging through the off colours and ending at the end of the scale beyond which diamonds are considered to have a fancy yellow colour. You should be wary, though, of jewelers offering fancy yellow coloured diamonds. Sometimes they grade off colour yellows as fancies without a proper gemological evaluation by a recognized gemological laboratory. The term fancy beside any diamond colour 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 colour report and a diamond grading report from a recognized gemological lab that identifies the stone as being of natural colour origin and truly fancy in colour.

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.

Diamond Color Grading Procedure

  • To be graded, diamonds must be loose stones, because once a diamond is set into metal the metal can affect its colour.
  • Diamonds are placed table-down, pavilion-up and viewed with a 10X loupe.
  • A lettering system from D to Z is used to identify the amount of colour present in each diamond, with D awarded only to rare, totally colourless diamonds.
  • 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'.
    based on the limitations of grading while the diamond was in the mounting.

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 colour graded loose and with the proper equipment. The stones should be upside down to provide the best viewing of the crystal colour. 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.

Fluorescence
Two thirds of all diamonds fluoresce to some degree but how they do so depends very much on the type of ultra violet light they are subjected to. In the jewelers shop there are many bright lights specifically designed to show of "any" diamond to perfection. This is a light that is very different to sunlight or natural daylight and explains why it is always important, when purchasing diamonds, to look at them in the light to which they will be exposed when being worn. Otherwise you might buy a diamond that presents quite a different, and to you, unsatisfactory appearance after you have walked out of the shop with it.

Strongly fluorescent diamonds tend to take on a bluish tint in sunlight and this can affect the color grading also. The price of diamonds is dependent on their visual appearance so fluorescence is a very important factor here.

Sometimes a lower colored stone, as diamonds are commonly called in the diamond business, at the bottom of the scale can attract a higher price if it is strongly fluorescent.


Diamond Lite

A Diamond Lite is an instrument that, using filtered fluorescent lights and a dull white background, creates the ideal lighting and background conditions to best view the color of diamonds. Diamonds will be placed face down so that you are more easily able to view the true body color of a diamond. It is generally used in conjunction with a Master Color Set of diamonds.


Master Color Grading Set of Comparison Stones

A Master Color set is a group of diamonds or CZ's that will, in a step-wise fashion define a range of diamond color. For example, each of the colors D through K on the Color Grading Scale would make and excellent Master Color Grading Set. By comparing a diamond with the stones of the Master Color Set the color of that diamond can be determined.

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.

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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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