Color is one of the most important factors to consider when determining the value of a diamond. The fact that two diamonds with the same carat weight, shape, size after processing, and clarity differ only by one degree will greatly change their material value. Diamonds occur in many colors. The most common colors are listed from colorless to light yellow. Diamonds in cognac, green, ocher, pink, red, and blue are rarer, and these are called fancy colored diamonds. Although red, blue, and pink colored diamonds are very rare, the most valuable diamond is the colorless diamond. So how do you think the color of a diamond is graded?
Since there is no faultless memory of the original color of diamonds, the most effective tool for grading diamonds is to use a sample diamond set. This method is a method of determining the color grade of a diamond by comparing it with other diamonds whose color grades are known. Color grading requires great skill, but there are certain lines and guiding techniques that are followed. The terms used to describe the various degrees differ in each system, but in fact, the degrees are similar. The color grading system used by the International Institute of Gemstone Science (IGI) is universal and parallels the GIA system.
For many years, many different terms were used to describe the color of a diamond. Many of these terms, which are still widely used today, came from the regions where the diamonds were found. Some of these terms include Wesselton, Cape, Jager, Premier, and River. The term “Wesselton” comes from the Wesselton mine, where diamonds are mined to a better degree than any other mine.
Hence, Wesselton is the name given to very light-toned diamonds. The term “Cape” comes from The Cape of Good Hope, located at the tip of the country known today as the Republic of South Africa. The term “Cape” is used for diamonds of a light yellow shade, as the average production of South African mines is yellower than that of Brazil. Today, yellow-toned diamonds are called “Cape stones”.
The term “Jager” comes from the Jagerfontein mine. The large quantities of diamonds mined from this mine were mostly light bluish diamonds with a distinctive luminescence. The term “Premier” is taken from the Premier mine. This mine produced diamonds with distinctive yellowish body color. These diamonds are yellowish in color but have a light blue nebula appearance with a strong blue glow. Therefore, the term Premier is used for such diamonds. The term “River” is used for good quality stones found in rivers and alluvial deposits.
In general, it was a problem that diamonds mined from a mine varied in color. Therefore, when these terms were widely used, no diamond dealer could agree on the color grade of the diamond (for example, the definitions of the terms were different). A simple example would be that when two separate companies talk about “extra white” or “blue-white” diamonds, they do not mean the same color grade.
The term “blue-white” is the most used term when talking about the color of a diamond. The indiscriminate use of this term when describing color grades, from colorless diamonds to diamonds with a light yellow hue, poses a problem. Therefore, in the international consensus, “blue-white” is defined as follows: Only colorless diamonds or stones with a bluish tint can be referred to as “blue-white”. However, these diamonds are very rare and are not usually found in jewelry. There are many reasons why this term is misused.
Most importantly, if a diamond is viewed through the crown in daylight, it can reflect the bluish color of the blue sky. The second reason is that diamonds scatter light. The third reason is that certain stones react uniquely to ultraviolet light.
What Is Diamond Color Grading?
If a diamond does not have one of the fancy colors and is rated high on the color chart, it means that the diamond is actually a colorless diamond. This is the opposite of all other gemstones. If a gemstone has a good grade in the color chart, it indicates that the gemstone has a dark intense color. Conversely, if a diamond is described as a well-colored diamond, it means it is a colorless diamond. Differences in the color determination are difficult to spot even for an experienced diamond expert, and they are not even noticeable to the untrained eye.
When a diamond is attached to a ring and is only seen from the tableside, the ordinary customer will not be able to distinguish between the top few grades on the color chart. Another important factor when describing the color of a diamond is that if the diamond has a yellowish color, one should not describe it as “limp colored” or “bad colored”. This will have an undesirable effect on the sale of diamonds, as these expressions give the impression that the yellowish-toned diamonds are not beautiful and not valuable.
The main requirements for color grading are:
- Write down your first impression of the color.
- Compare diamond with sample diamond set.
- Make your grade based on the grade of body color.
- Specify a color grade.
Procedure:
- Clean the apple thoroughly.
- Use filtered white light against ultraviolet rays.
- Use a non-fluorescent matte white background.
- Place the diamond on the table side down and close to the sample diamond.
- Examine the diamond.
- Compare the diamond with the sample diamond by moving it side to side.
- Examine the diamond under ultraviolet light to see if it radiates. Note the degree of glow.
- Make sure the color grade of the diamond is correct against random color changes.
- Record the characteristics of the diamonds in the sample diamond set, such as measurements (diameter and height), weight, spots.
Suggestions:
- Clean the diamond meticulously.
- Do not let the diamond you are trying to grade touch the sample diamond, because the colors of the diamonds can interfere with each other. This will have a negative effect on your first impression of the color of the diamond. It can also cause diamonds to be scratched.
- Beware of poorly proportioned stones. A diamond with a flat cone may appear lighter in color. On the other hand, a deep cone diamond may appear darker than a well-proportioned diamond. Particular attention should be paid to diamonds with thick arches. Because the thick belt greatly affects the color of the diamond.
- Blow quickly on the diamond to neutralize the reflections. As the diamond begins to clear, the primary color will be perceived more clearly.
- Don’t make the grading process too long. After looking at the strong colors, rest your eyes for a while before you start grading another diamond. If you are going to grade colored stones, pause the color grading of the diamonds for a while. Constant exposure of your eyes to bright colors can affect your ability to distinguish color differences.
Choosing the Right Light When Diamond Grading
Correct light sources and a suitable environment are essential if color grading is to be done correctly. Daylight is not sufficient for color grading because it can vary from day to day or from place to place, it is not consistent. Today, a “diamond lamp” is mostly used as a light source in laboratories. The diamond lamp consists of a low-intensity fluorescent bulb and a cool white bulb that filters through the frosted layer.
The diamond lamp is the best choice when it is the only light source in a semi-dark room. It is very important that the backgrounds of the graded colors are completely white and do not reflect light. Therefore, an extremely white, matte paper should be used. Luminescent diamonds will show better colors if viewed in daylight due to the presence of ultraviolet light. For this reason, luminescent diamonds should be graded under a daylight lamp with a special filter, such as a “diamond lamp”.
Luminescence is a property that makes certain minerals glow when exposed to Ultraviolet light or X-rays. The source of this property is the electrons in the atomic structure of the mineral, which are activated and rise to higher energy levels. When these electrons descend to their original energy level, they absorb visible light, that is, they glow.
More than 50% of gem-quality diamonds glow under a strong, long-wave ultraviolet light source, however, not all luminescent diamonds show much change in their original color in artificial light or in daylight. Diamonds usually glow blue, but they have also been seen to glow in other colors such as white, orange, yellow, and green. The luminosity of diamonds does not affect its value as long as it does not give the diamond a cloudy appearance. If they are not nebula, diamonds that glow blue will have a better color in daylight, which may even add value to them.
Diamonds with intense ultraviolet radiation give the stone a bluish tint and change its original color. A glowing diamond appears in better color than it actually has, in a sense the yellow hue can be diminished by radiation, and many jewelers use this property to enhance the diamond’s appeal. A person needs to be careful when purchasing a set of diamonds to use in a piece of jewelry. If only some of the stones are luminous, the glowing stones will stand out more in daylight, and even their original color may appear different.
A diamond that changes color when viewed alternately in daylight and artificial light is called a “Premier” diamond. A “Premier” diamond is bluish in daylight and yellowish in incandescent artificial light. The name comes from the Premier mine, where diamonds with this characteristic were mined. Nowadays, the term is used to describe a variety of diamonds with luminous properties, regardless of region. However, this term is not used for colorless diamonds that glow blue. For diamonds, the luminosity should be measured and the measurement results are written on the label.
Diamond Color Grading Procedure
Before grading the color of a diamond, the diamond must be meticulously cleaned. Specimen diamonds should always be kept clean. Write down your first impression of the color of the diamond you are grading. Try to identify the sample diamonds with the closest color to the diamond you are grading. Hold the folded diamond grading paper between your thumb and forefinger. Place the sample diamond between the folded paper with the table side down.
Place the diamond to be graded in the same position between the sample diamond and the paper, a stone’s distance from it. Squeeze the grading paper and lay it on its side so that the edge covers the crown, only the arch to tip looks like a small pyramid. Move the stone you are examining to the right and left of the sample diamond. With this move, you can see if the diamond you are trying to grade is darker, lighter, or the same color as the sample diamond. Avoid moving the sample diamond. Always hold and move the diamond until you make a final assessment.
Compare the shades, not the colors, of the diamonds. Classification is based on the color saturation of the diamonds. When comparing a diamond to a sample diamond, it is very important to keep in mind that color determination is based on the amount of color, not the color itself. Because the body color of diamonds varies greatly from yellow to gray and even brown. One should be aware that sometimes in certain areas, or even all over, of a diamond there are concentrations of colors that contrast with the primary color of the diamond. You have to be careful when grading, brown is perceived as having a darker shade than yellow, so there is a tendency to give lower grades to brown-toned diamonds.
It should be noted that a correct color grading can only be completed under the correct conditions described above and after consistent work. Usually, a person’s first impression of the color is the best. Keeping the review process long will affect your initial judgment. If you are having trouble deciding between colors, rest for a while and try again. If you have decided on the color grade of a diamond very late in the day, it is recommended that you leave the grading to the next day, as your eyes may be tired, as this will affect your judgment.
Diamond Grading With a Sample Set
A gemstone dealer or jeweler should have his own set of sample diamonds so he can compare the diamonds he buys and not overpay for diamonds one or two degrees lower than he expected. The first step in making an accurate color grading is to select the diamond to prepare a sample comparison set. The use of a sample diamond set gives the person a chance to make a standard comparison when determining the color. When preparing a sample set, there are certain conditions one should keep in mind. There are some conditions to consider when preparing a sample set for comparison:
a) The minimum weight of the diamonds used in the comparison set should be 0.40 ct, and all the diamonds in the set should be approximately the same size.
b) The sample diamonds to be used for color grading need not have a high degree of clarity, but diamonds that do not affect the color or transparency of the internal crystal spots should be selected. Diamonds with additional crystals of dark or color should be rejected.
c) The color of the diamonds in the sample set should be ordered from colorless to light yellow. The sample diamonds used for comparison should start from the lightest color grade on the left and continue gradually from darker tones. Brown or gray should not be used in any way. The color chosen for the highest grade depends on what kind of diamonds the jeweler is dealing with. If he only uses grades G, H, I, and J, he need not invest in diamonds grades D and E but will need grades F and K.
How extensive the sample set will depend on the demands of the person’s job. There are color grades that range from “0+(D)” to “20+(Z). However, such a comprehensive set is rarely needed. While the emphasis is placed on better-colored diamonds, three to eight sample diamonds are preferred. Everyone has to find the grade to cover their inventory.
d) Diamonds that glow strongly under ultraviolet light should not be used in the sample color set because the color of the diamond we will use for comparison must be constant (the color of strongly luminous diamond changes in daylight and artificial light).
e) Sample diamonds for comparison should be well cut and well proportioned. Diamonds with very thin or very thick crowns, or very deep or flat cones, or very thick belts should be avoided. If the proportions of the diamond are not good, it may appear in a different color. E.g; A deep cone will appear darker, and a flat cone will appear lighter compared to a well-proportioned diamond. Cone depth between 41% and 46% is the most suitable for comparison. Crown height ratio is also best between 11% and 16%.
f) A record of the exact weight, degree of clarity (with smudge diagram), and measurements of each diamond in the sample set should be kept. This registration will be necessary in case of the mixing of diamonds, so in a sense, it will always be possible to trace the diamonds in the sample set.
g) The color grading of the diamonds should be done in a semi-dark room, the expert who will do the grading should not grade for more than one hour without rest. Because the visual ability of the person will decrease due to fatigue.
h) A specially folded piece of white paper is used for color grading.
The standards required in the selection of the sample diamond set to be used for comparison are as follows:
- Weight
minimum size: 0.40 ct.
Choose stones of approximately the same size.
- Clarity
Use diamonds with a clarity grade of SI, VS or higher, and high transparency. Diamonds with colored spots are not suitable.
- Dimensions
Cone depth: 41%-46%
Crown height: 11%-16%
Thick arched stones are not suitable.
- Number
You must have enough diamonds on hand to accurately determine the color grade.
- Diamonds not to be used
Diamonds with luminous properties
Diamonds with body colors other than yellow
Color Grading Procedure for Diamonds in a Jewel
The color of the diamond perceived by the examiner is clearly influenced by the color of the frame used when installing the diamonds. Usually, white metal is used for the frame. White gold and neutral-gray platinum are the best choices for mounting diamonds because the yellow metal bezels affect the color of the diamonds. Colorless, or nearly colorless, diamonds mounted in yellow gold will appear to have a yellowish color.
Diamonds, which appear yellowish when viewed from the top, are usually mounted using yellow gold. Because, in this way, the yellow tone appears lighter. However, when mounted with white gold or platinum, the yellow color will stand out more easily than when made with yellow gold. It is very important to know that there will be differences in the color grades of single diamonds and diamonds set in jewelry. Free diamonds are color graded perfectly and accurately. But the same is not true for mounted diamonds.
Because; 1) The cone part of the diamond that needs to be graded is not visible due to the frame, 2) The color of the metal used when mounting affects the actual color of the diamond, 3) Mounted diamonds cannot be easily cleaned. All these factors make color grading of mounted diamonds difficult. To make the color grading of diamonds mounted in a location as accurate as possible, one should proceed carefully and take into account all of the recommendations.
A summary of the requirements for color grading of mounted diamonds
- When grading the unknown with a sample diamond, 10x magnification is best.
- Apply the same optical conditions as possible for color grading free diamonds to mounted diamonds (white background and good lighting).
- Take your tweezers and hold the compared diamond with the table parts facing each other.
- Trying to compare the cone parts will be problematic. It is best practice to compare the crown of the mounted diamond with the crown of the sample diamond. Always place the sample apple on the left and the studied apple on the right. The jeweler is strongly advised to give the diamond a color grade. E.g; if a jeweler’s diamond assigns a grade of H, it is necessary to show the customer that the color is between G and H. This range of colors is easily explained, as mounted diamonds are very difficult to grade.
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