Knowledge Quest Series - COLOR
Color is an important value element in diamonds. Color grading, under even the most prefect laboratory conditions, is subjective. This is not to say that it is willy-nilly as the varying professional grading opinions should be close to one another or matching. Since color is a factor that consumers must be aware of in their buying decision, it is important for them to fully understand what "color grade" is all about.
A "color grade" for white diamonds is not a hue. In other words, we are not assigning colors such as red, blue, green, et cetera. Although diamonds are available in these and other hues, the color grades assigned by graders are referring to tint.
If the secondary tint is yellow, for example, the grade tells the reader how much yellow there is. Colorless, the highest color grade, simply means that no color exists. An "H" color, tells us that some color exists but it is most likely not detectable by eye without a special set-up. We will discuss more on the specific grades later in this article.
Imagine that you are looking at a skyscraper which is appears for the most part to be one wall of windows. Let us further image one row of those windows to be our color grading spectrum. On the far left-hand side of the row is a window with absolutely no tint. On the other extreme end is a window that is a deep tint that makes it appear dark. In between, you guessed it, the windows graduate from colorless to dark.
To make our illustration even more realistic, imagine that each window is also graduated in tint. Thus a window graduated from the tint of its left neighbor to the tint of its right neighbor. But, each window, regardless of its graduating tint, is given a letter. Now you are provided this row of windows as a master set for color grading (actually tint grading) a sheet of glass. Your task is to match the pane of glass to the window that is closest to it and assign it that letter.
Individual diamonds within diamond master sets have a letter. But they may fall on the high-end, middle or low-end of that assigned letter grade. For example, and H-I master diamond signifies that the master diamond is an H but on the low-end of the H grade (almost a grade of I). Add in the human factor, ultraviolet reaction by some diamonds and you have subjectivity.
Diamonds, as we mentioned before, can come in a variety of colors. These fancy colored diamonds can be rare and thus, expensive. But you are most likely wanting to know what tints are involved in the color grades of white diamonds. The most common tints are yellow, brown and grey.
Although we call them white diamonds, they are not really the hue white. They are colorless diamonds that are with or without some tint as a secondary color. It is the lack or presence of a tint that we are measuring and how much of it there is.
There is no one-way to color grade diamonds. Some approaches are questionable while others are considered more accurate. All are subjective to some degree.
By eye: Some appraisers, retail jewelers, wholesalers, diamond cutters and in-house graders simply look at the diamond and assign a color by experience. Obviously, this is the most subjective approach as any number of factors can interfere with the process enough to cause inaccurate results.
CZ Sets: There is a widespread practice of using master grading sets that are comprised of cubic zirconias (CZ). The accuracy of the CZ sets rests with the company that graded them. In most cases, they were not graded by a laboratory that specializes in color grading master sets such as Gem Trade Laboratories at the Gemological Institute of America (GTL-GIA). We admit that there are available CZ sets that have been carefully graded and these are far more accurate than the majority of sets being used.
One of the drawbacks pointed out is the fact that CZ has a "read-through" effect. If you place a round brilliant cut CZ table down over a line drawn or printed on a piece of paper, the line not only is readily visible but doubled in appearance when it passes under the CZ. A diamond will not provide the same result - the line is not visible at all. A logical conclusion would be to assume that CZ masters are affected by the snow-white color of the grading trays because the color comes through to the eye of the grader. We have not found any scientific studies nor have we experimented to determine for ourselves if this is true. Instead, we have employed our less doubtful approaches to determining color.
Machines: More than one machine has been introduced into the diamond grading arena that grades color. Each machine's user manual clearly states that they are to be used as a second opinion and that master sets are to be the primary approach to color grading. Some experiments have shown that machines seem to have an average of 80% accuracy against laboratory graded diamonds. Factors, like fluorescence, cut style, et cetera all show lower accuracy when graded by machines.
However, there is no denying that customers are often more strongly persuaded by a machine color grade than a skilled human grader's conclusion. That needle or readout jumping to a color grade will most often be taken as gospel. With an 80% accuracy rate, machines are definitely subjective in nature and less accurate than trained and experienced diamond graders.
Diamond Masters: Considered the best approach for grading diamonds' color, a set of diamond masters used by a skilled grader can reduce the subjectivity considerable. However, there are several factors that may cause inaccuracy.
The masters must be graded for grading. Assembling a master set from stock that has never been tested and certified as a master set is only as accurate as the person who assembled the set. If he or she were slightly color blind, for example, how accurate will the set be? The trade accepted grader of such sets is GTL-GIA. Each set has a number.
Even if a grader has a set, the set may be dirty and that would result in inaccurate conclusions. Since diamonds that are un-mounted, as would be diamond masters, are handled with tweezers, eventually metal is transferred to the diamonds' girdles. This will impart a grey tint to the diamond masters causing inexact grading.
The size of the masters limits the accuracy. Many sets are within the half-carat range. For most grading this is acceptable. However, a large diamond, for example a 3 carat sized diamond, the result is not much better than a guess. Appraisers usually cannot afford sets that have one carat diamond masters, therefore the reliance on grading laboratories is a solution.
The environment has a serious affect on accuracy. Ambient lighting that interferes with the special light used for grading will cause problems. If the grader wears a blue shirt, for example, the color grades may be higher. Is the grader taking medicine that may affect his or her vision? Did they get enough sleep the night before? When was the last time they were tested for hue discrimination (color blind testing)? What time of the day was the grading being conducted? Is the diamond fluorescent? How many masters are there in the grader's set? Which color grades are there in the set (are there no diamond masters in the J-K range which happens to be the diamond's color grade range)?
By now you should be convinced that color grading diamonds is subjective - regardless of the method or by whom (appraiser or laboratory, for example). A vendor that has a laboratory report or reports, who also re-grades the diamond using his or her own certified masters to verify the laboratory's conclusion may be your best bet.
A small percentage of diamonds will react to ultraviolet light by fluorescing. The strength of the reaction varies from diamond to diamond. Fluorescence can be a concern when acquiring a diamond.
Ultraviolet lights come in two basic types. One is short wave. This one can sunburn you. Gemologist know not to look into the lamp or they run the risk of damaging their eyes. The other one is called long wave and although considered a lot less dangerous than its short wave cousin, nevertheless staring into it is not advised.
Some diamonds will react by fluorescing only with short wave ultraviolet exposure. Other diamonds react only to long wave. And, of course, some diamonds react to both ultraviolet situations. Your concern is primarily with the strength and color of the reaction regardless of the type of ultraviolet. Yes, some gemologists disagree with the all encompassing statement that includes both types of ultraviolet light but sunlight, a place where you will be showing off your diamond, has both types of light, thus making them both a consideration. After all, you are not going to only be indoors.
Let's tackle color first. Although the ultraviolet reaction color can be almost all colors, some are less desirable than others. A chalky color, such as yellow, can make the diamond appear weird when reacting. Of all the colors, blue is perhaps the most common and most acceptable. Blue, being opposite yellow in the color wheel (that wheel used to explain color mixing for artists and other professions that utilize color) tends to neutralize the commonplace yellow tint found in near colorless and lower grades. If the secondary color of the diamond is not yellow, then a bluish color reaction to ultraviolet light would not be useful.
Basically, a diamond that fluoresces blue can be good but not if the reaction is strong.
That brings us to discussing what is meant by a strong fluorescence. Some diamonds have a strong reaction to ultraviolet light and tend to look oily or greasy when viewed in office light and sometimes even in sunlight. You will have the tendency to continuously wipe the stone in an effort to clean it all to no avail because it is not the least bit dirty but fluorescing. This is a strong reaction on the part of the diamond. It cannot be fixed. Any diamond that has such a look is one to avoid at any cost unless you like the look as a personal preference.
If you hold the diamond near a fluorescent lamp, like the ones gemologists use to a grade diamond's color, and it appears oiled - select another diamond. By the way, we are not telling you to use a black light but an ordinary fluorescent lamp like you probably have in your office. The logic is - you want the diamond to look its best in all environments, not just in the store where you are considering buying it.
If the diamond's reaction is weak to maybe what might be called medium, it may be alright. This may be an area where the expert you have selected to assist you in the selection of your diamond must advise you unless it is obvious that the fluorescence is not a concern.
Although major diamond grading laboratories mention the color and strength of the reaction to ultraviolet, they are often inconsistent. One laboratory, the AGS laboratory, does in fact use a master set of fluorescent diamonds to grade diamonds and this results in consistent results.
Fluorescence can be a hindrance when grading tint. If the diamond is reacting to the lamp used for grading, conclusions may not tell you what the real tint is. Shields, such as Lexan plastic™ can virtually block all fluorescence and provide the grader with a true color but this technique has not been accepted and employed by diamond grading laboratories. We, with all fluorescent diamonds, grade the diamond both with and without the plastic shield. Both results are provided for your consideration.
We have provided an in-depth article in fluorescence that you can read to increase your understanding of diamonds.
Some diamond cuts tend to hinder color grading. Take our tinted glass on the building example we presented earlier and imagine one sheet of tinted glass taken from one window. If the glass is a quarter inch thick, it will have a tint that may be barely visible. However, a sheet of glass with the same exact tint that is ten inches thick will have a noticeable tint although they are basically the same "color grade."
Some diamond shapes (or cuts if you prefer) have both thick and shallow areas. A marquise cut is a normal thickness in the center area (if we use the round brilliant cut as our standard for normal) and shallow depths at each tip. The center may show tint while the tips have none even though the diamond is an even tint throughout. Grading such a stone has to be performed at various angles towards the center and an average used for the final conclusion.
Large diamonds may show color while smaller diamonds with the same grade might not show any color (or less color as the case may be). A half-carat diamond of a J color may not show color without being turned on it's table and viewed from behind whereas a two carat diamond with a J color may face-up slightly yellow. The rule of thumb is that one carat is about when size makes a difference with J color graded diamonds. In any case, until you see the diamond or have someone check it that knows what to look for, do not blindly order such a stone as the results may disappoint you (or on the other hand be a bargain is the color does not show enough to be a problem).
Since you will be viewing your diamond in a face-up position once it is mounted, your concerns must focus on the following things.
The better the cut quality, the more difficult it is to see a diamond's color. Like staring into a lit light bulb, reading the wattage would be difficult. A well cut diamond masks its body color to a certain degree.
Since a well cut diamond actually captures a panorama of colors and transmits to your eyes in stereo, the environment's colors will affect your perception of the diamond's color. Laboratories try to eliminate such colorful sources of light and maintain a North Daylight standard of light. This standard is not often encountered in the real world and you should be prepared to examine your diamond in various lighting situations.
A factor that may influence a color grade would be hue discrimination - sometimes called color blindness. In colored gems this would be a major influence but in color grading diamonds, it has less impact. After all, instruments are available to grade diamonds. If the grader has problems seeing yellow, grey or brown, then they may have problems grading diamonds for color.
Most professional gemologists and appraisers grade color in the morning hours. As the day passes, it takes a toll on one's ability to detect minor color differences. Medications can also alter one's ability to ascertain color in a diamond.
If one looks at a color wheel used by artists, you will notice that blue is opposite yellow in the wheel. If one were to mix blue into yellow, the result will be a change towards white. The inside of color grading boxes is white. However, if the grader were to wear a blue shirt or blouse that reflects into the box (by being close to it), the resulting color grade of the diamond would increase. Even though the significance may not be great, a group of small increases could result in a grade increase or decrease.
As humans, we have our eyes in the front of our heads. This provides us with stereoscopic vision from which we can judge distances. What is not well known is the fact that one eye will be dominant. Sharpshooters know this well and they use their dominant eye for aiming. Do not assume that if you are right handed that you are right eyed as that may not be the case. In fact, your "master eye" may switch from time to time. Hold your hands together and form a circle with your fingers and sight onto a distant object through the hole. Now, close each eye in turn. If the object within the hole formed by your circle of fingers does not move, that is your "master eye."
How does this influence color grading in diamonds? We grade by placing the unknown diamond next to a master diamond. Is the unknown diamond darker or lighter in tint to the master? If it is lighter, we then move the unknown diamond to the next higher master and again make a comparison. This happens until the grader finds a match.
When a match is found, the unknown diamond is placed on both sides of the master diamond. That way, a consensus can be determined. Why? Because the "master eye" effect will cause the unknown diamond to look slightly different on one side of the diamond master than on the opposite side - depending on which of your eyes is a master eye.
If one were to take into consideration all the factors that influence color grading, the most important one is the type of light used. It has been said that all lights mimic "cool north daylight." Therefore, one cannot use harsh light sources, tinted bulbs, et cetera. A cool fluorescent lamp of 5,000 to 5,500 degrees Kelvin is the standard.
Do not be afraid to ask the vendor how the color grade was established. After all, it is your money that is on the table and you need to know everything in order to make an informed decision. This applies whether you are acquiring a diamond on-line or from a store. We recommend that you acquire your diamond from a qualified gemologist as that raises your odds of getting truthful information. Again, remember that it is your money and you have the right to ask and get an answer.
We have provided a list of possible questions to ask when considering buying a diamond. This list can be used in a jewelry store environment or with online vendors.
Our procedures vary with the diamond involved. If the diamond is an important size - it most likely will be passed through laboratories as well as our in-house grader. This may result in varying color grades. One laboratory, for example, may call the color H while another equally reputable grading facility may call it a G. That is what subjectivity is all about. However, we will also grade the diamond's color in-house and provide that opinion.
We have a master set of diamonds just for fluorescence that was checked by AGS laboratory against their master set. Although this is still subjective, it does narrow the subjective nature of grading down considerably.
Although you may be thinking that this article on color grading was long, we could have said a lot more. The purpose was to make you aware of the subjectivity involved, all the minor and major influences that professionals are challenged with but most important to be cognizant that even laboratory grading reports are subjective.
