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All gemologists say they can do diamond color grading just like the GIA Lab does it. Every new gemology student earns a degree of confidence in their ability to make these judgments. The truth is that no one is completely consistent with GIA grading as the system is subjective and unusually formulated. The GIA itself is satisfied with less than 100% repeatability. No one else can expect to do it better under these circumstances. There are reasons for this situation and this essay is not written as an excuse for shoddy or careless color grading
A gemologist/grader must practice their skills frequently to stay on top of the game. Your eyes need practice, proper lighting environment and reliable master stones. You can’t reliably grade diamond color as an occasional hobby, in unusual lighting, or without comparison stones. You can easily mislead yourself and anyone who depends on your opinion if you don’t follow these common sense guidelines.
Diamonds are color graded unlike any other transparent object or colored gemstone. The larger a diamond becomes the darker it gets. This is from increasing absorption of light as the material gets thicker. Think of the edge view of a glass top table. It is deep green, yet the glass, face up, is virtually colorless. If the table top was diamond it would be graded as colorless based on a small sample chipped from it or by its best view, which is through the top. If someone wanted the table top looked at as if it was a fancy green diamond, they’d grade it from the side view and not worry that from another angle it looked colorless. A “D “color diamond is pretty much always colorless, no matter how large, but of you see a 20 carat “F” color, it is not the same visual color as a 1 carat “F” color. There is an interpretation being made by a knowledgeable gemologist, we hope. That gemologist is thinking “What color would the material be if it was only 1 carat or ½ carat in size?” That’s the color one would is assign. I call it “AS-IF” grading. You may call it something less nice if you want, but that’s the reality.
One must remember the huge value of diamond rough material. This is the strong economic reason for color grading in this very unusual way. It also shows the influence of economics on the reality of laboratory grading in the diamond business. When we think of laboratories in general, we think of sterile environments and places of pure science. When one talks about gem laboratories there is a heavy mix of business, smoke, mirrors and science all tossed into a mixing pot. We get results out that are somewhat surprising and unique, but we can live with it and have for more than 60 years.
UV fluorescence plays a role in how our eyes perceive body color in diamonds. The GIA and others have made some changes in the lighting used over the past decades. This has an effect on grading outcome depending on whether some, all or no UV is allowed in to light the diamond when it is being graded. There is no truel consensus on how much UV is okay, but I believe the GIA uses a consistent lighting for their grading which has some UV in it. I think AGS eliminates most UV. Again, I could be wrong or out of date on this. My own lab uses some UV in the lighting. It makes sense to use a realistic environment for grading, but there are many “realistic” lighting opinions out there.
How do we expect to do better? We can argue until we are blue in the face about what sort or amount of UV can be in the lighting we use. We can argue over the proper color temperature of the grading lamp. Cool White, Daylight, etc. We may always differ. But, the question remains, “Can we do this better?” I believe we can. Technology now exists to grade the color of round diamonds with lighting that is much like what labs use and does have some UV component. It is a lot like the GIA lighting model one might say. Once the data is grabbed from many digital views of the stone it is also compared to a database to see how the GIA graded similar diamonds. In this way, one uses science and statistics to assess color grade. This gives us accuracy in the final grading that has never been available before in any simpler machine or to any gemologist. Every device and every person has a problem with colors that cross over into the next higher or next lower color. These will forever be a judgment call for a human grader and a statistical call for a device. No amount of finely dividing colors will totally eliminate cross over points, but we can make them less bothersome by a refined method such as machine grading of color.
All the world's major diamond grading labs are striving to give better and more accurate grades. In today’s technological world, consumers and gemologists all expect and demand more accuracy and consistent results. Its an exciting period in the diamond business. So much is changing.
A gemologist/grader must practice their skills frequently to stay on top of the game. Your eyes need practice, proper lighting environment and reliable master stones. You can’t reliably grade diamond color as an occasional hobby, in unusual lighting, or without comparison stones. You can easily mislead yourself and anyone who depends on your opinion if you don’t follow these common sense guidelines.
Diamonds are color graded unlike any other transparent object or colored gemstone. The larger a diamond becomes the darker it gets. This is from increasing absorption of light as the material gets thicker. Think of the edge view of a glass top table. It is deep green, yet the glass, face up, is virtually colorless. If the table top was diamond it would be graded as colorless based on a small sample chipped from it or by its best view, which is through the top. If someone wanted the table top looked at as if it was a fancy green diamond, they’d grade it from the side view and not worry that from another angle it looked colorless. A “D “color diamond is pretty much always colorless, no matter how large, but of you see a 20 carat “F” color, it is not the same visual color as a 1 carat “F” color. There is an interpretation being made by a knowledgeable gemologist, we hope. That gemologist is thinking “What color would the material be if it was only 1 carat or ½ carat in size?” That’s the color one would is assign. I call it “AS-IF” grading. You may call it something less nice if you want, but that’s the reality.
One must remember the huge value of diamond rough material. This is the strong economic reason for color grading in this very unusual way. It also shows the influence of economics on the reality of laboratory grading in the diamond business. When we think of laboratories in general, we think of sterile environments and places of pure science. When one talks about gem laboratories there is a heavy mix of business, smoke, mirrors and science all tossed into a mixing pot. We get results out that are somewhat surprising and unique, but we can live with it and have for more than 60 years.
UV fluorescence plays a role in how our eyes perceive body color in diamonds. The GIA and others have made some changes in the lighting used over the past decades. This has an effect on grading outcome depending on whether some, all or no UV is allowed in to light the diamond when it is being graded. There is no truel consensus on how much UV is okay, but I believe the GIA uses a consistent lighting for their grading which has some UV in it. I think AGS eliminates most UV. Again, I could be wrong or out of date on this. My own lab uses some UV in the lighting. It makes sense to use a realistic environment for grading, but there are many “realistic” lighting opinions out there.
How do we expect to do better? We can argue until we are blue in the face about what sort or amount of UV can be in the lighting we use. We can argue over the proper color temperature of the grading lamp. Cool White, Daylight, etc. We may always differ. But, the question remains, “Can we do this better?” I believe we can. Technology now exists to grade the color of round diamonds with lighting that is much like what labs use and does have some UV component. It is a lot like the GIA lighting model one might say. Once the data is grabbed from many digital views of the stone it is also compared to a database to see how the GIA graded similar diamonds. In this way, one uses science and statistics to assess color grade. This gives us accuracy in the final grading that has never been available before in any simpler machine or to any gemologist. Every device and every person has a problem with colors that cross over into the next higher or next lower color. These will forever be a judgment call for a human grader and a statistical call for a device. No amount of finely dividing colors will totally eliminate cross over points, but we can make them less bothersome by a refined method such as machine grading of color.
All the world's major diamond grading labs are striving to give better and more accurate grades. In today’s technological world, consumers and gemologists all expect and demand more accuracy and consistent results. Its an exciting period in the diamond business. So much is changing.
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