Testing… Pink, Yellow, Blue

The GIA puts its color diamond graders through rigorous testing

Although nature created the colored diamond, in today’s marketplace that diamond is just a beautiful stone without ancestry. It must earn its pedigree in the form of a certificate. While there are many labs examining and grading fancy color diamonds, for the U.S. market, a Gemological Institute of America (GIA) cert is the most widely used. And in order for that certificate to carry weight in the industry, it has to be backed up by the evaluation of a trained colored diamond grader.
The process of becoming a diamond grader begins with a series of seven tests that eliminate candidates with limited color acuity, as well as those who don’t have the ability to “reason” their way to the essence of a diamond’s color. That ability, acco
rding to John King, chief quality officer of the GIA Laboratory, is crucial to colored diamond grading.

Approximately one-third of those who go through the GIA vision screening, which can be completed in about three hours, qualify on their first attempt. Some who don’t make it through on the first try return to go through the testing again, and, John King says, “We have seen improvement in some who have taken the tests more than once.”

In the general population, 8 percent of men and just .5 percent of women have red-green color blindness, the most common form of color vision deficiency. Outside that group, a person’s color vision can range from superior vision — able to discern the most subtle color variations — to vision that, while not considered color blind, is also not particularly sharp.

The innate color vision of candidates interested in becoming graders is evaluated first at GIA because it is an essential, nonnegotiable qualification for the job. Graders may rotate among various tasks in GIA’s lab, but they need excellent color acuity to perform any job on any diamond, whether colored or “colorless.” The differences between a Y and Z diamond or between fancy light and very light colored diamonds are extremely subtle and a superior natural color acuity is necessary to first “see” those subtleties and then to identify and evaluate them.

The color vision test, familiarly known as the “dot” test, is the universal testing tool for identifying color deficiencies in individuals. It is a standard detection test used to screen applicants for work in a wide variety of assembly, design and laboratory industries. In the test, the subject is shown a sequence of test plates flashed on a screen, each of which contains a combination of various colored dots. Within the background dots, dots in contrasting colors form a number, which the applicant is asked to identify in five seconds. With each successive test plate, the contrast between the background and the number grows ever more subtle and more difficult to discern. For those with color vision deficiencies, the numbers quickly become invisible. In fact, many people first discover they have a color deficiency when they face the colored dot patterns of the test and fail to see the numbers.

The remaining six tests in screening diamond grading applicants at GIA are conducted with the Gretag Macbeth Judge II light box, which is equipped with extremely bright, extremely white light. Coincidentally, the Judge II light box is commonly used to grade diamonds.


The Farnsworth Munsell 100 Hue Test asks the candidate to organize 93 colors into four groupings, reflecting the progressive, subtle gradation of colors from one end of the spectrum to the other. The individual being tested physically moves different colored pegs within two stationary colored panels in order from the high — i.e., vivid — to low — i.e., pale — range of a particular color. The test is carried out beneath simulated daylight provided by the light box, at a distance of approximately12 inches to 15 inches. The test taker has 15 minutes to sort out the four groups of colors.

For the “color attribute” aptitude tests using Munsell color chips, the applicant is first given a brief explanation of three different color attributes — hue, tone and saturation. Hue is the aspect that describes colors by specific name, either by the primary color, such as red, green, or blue, or by some intermediary color between the primary colors, such as reddish orange or bluish green. Tone describes the lightness to darkness of a color; saturation measures the strength or purity of a color.

In a sequence of two tests using 25 pairs of Munsell color chips arranged on small cards, the applicant must consider the appearance relationship among these three color attributes. In the first test, the chips have been chosen so that two of the three attributes are the same; the applicant must discern the attribute that is different. For example, the hue and tone may differ but the intensity of the color is the same. In the second test, two of the attributes are different and the test taker must find the matching third attribute. For example, both chips have the same tone, but the hue and intensity differ. Each test must be completed within 15 minutes.

Color matching is the subject of the Macbeth Match Point test, in which the candidate moves two scales of a color gradation slide back and forth in relation to each other to find the point at which they match as closely as possible. An exact match is not possible in this test. In Match Point, the so-called “metameric” effect of different light sources is being judged — the phenomenon in which two objects match in color under some lighting conditions but not others. Five minutes is allowed for this test.

Finally, in the concluding two tests, the specific tasks and skills of a diamond color grader are evaluated. The first is the most controversial aspect of diamond color grading as carried out by the GIA — stone-to-chip comparison — in which diamonds are compared to Munsell color chips.

The controversy stems from the fundamental differences in the two objects. The chip is flat, even in color and opaque, while the stone is three-dimensional, absorbs and reflects light and is transparent. Because of these differences, this test requires a huge leap into a realm where apples are indeed being compared to oranges. The applicant must find the color chip that is closest in hue, tone and saturation to the diamond being examined. According to GIA, “this test determines if the applicant can look beyond the complex visual details of the diamond and find a single overall appearance that is close to the overall appearance of the chip color.” The applicant must compare six pair-ups within 35 minutes.

Munsell chips are used only when the lab does not have a comparison stone to use. It is not possible for GIA to have a real diamond as a comparison stone in every single shade of diamond submitted to them for certification. Diamonds occur in thousands of tones; even if such stones could be found for every match, no lab could afford to buy all of them.

In the final GIA test, an individual is asked to grade five yellow diamonds against a range of GIA yellow master stones. Yellow diamonds are used because they constitute the broadest family of hues within one color category and also because they make up about 60 percent of the colored diamonds submitted to the lab for grading.

Although the applicant is now grading apples against apples — a specific stone against a master stone — the stones vary in cut, once again adding to the complexity of the test and mirroring the actual real-life practice of grading diamonds. Assessing the saturation of color between a pear shape and a round, for example, requires the ability to consider all the angles of the two diamonds in order to discern depth of color. Although diamonds are graded face up, the grader still has the opportunity to rock the diamond back and forth to observe the color. The applicant has 20 minutes to grade five yellow diamonds and place them within categories ranging from fancy light to vivid.

In all six of these color comparison screenings for a position as a GIA diamond grader, King says, “We are teaching a way of observing that will allow the grader to gaze at the color rather than the details.” He compares the process to seeing a Seurat painting. If you look at it up close, you see the separate elements that go into the painting. When you step back, you get the overall impression — the individual “dots” of color merge to achieve the image the artist had in mind. So it is with colored diamonds. “After the testing, we mentor them for weeks. In training, you begin to understand their reasoning skills; how you think is part of the way you see.” King says the successful grader must be able to put together all the observations of the diamond to come to a conclusion. “They must reason their way to a decision,” he adds.

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