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Understanding the 4-C's of Diamond Grading

When a professional appraiser is grading a diamond a chart is used to analyze each stone. Factors such as weight and cut are quantitative and measured while other characteristics, such as color and clarity, are graded by comparison, and, well, let's just say expertise and “feel”.

Many consumers, especially those who do not have a diamond buyer, need to rely on certificates from rating agencies for their diamonds when comparing one to another. To complicate matters for consumers, there are several different rating agencies, each having very different industry standards.

Therefore, when buying diamonds, it is important that you know who graded the diamond and what standard  they used - even though two stones might be exactly the same on paper - when seen in person they may look totally different.

Below I have outlined the guidelines used by the GIA (The Gemological Institute of America), which is where I received my training. I chose GIA as I found their standards to be the most rigorous in the industry. When price shopping and purchasing diamonds I am of course partial to their practices and when buying, especially one without an official GIA Certificate, I use the same criteria a diamond grader from the GIA would use to evaluate and rate the diamond I am looking at.

I recommend using the GIA standard when buying diamonds with or without a certificate. There are times when I buy or sell a non-certified diamond, and if selling a non-GIA stone I clearly explain the characteristics and differences in terminology to my clients. I recommend if buying a non-GIA certified diamond you clearly understand the difference, as you will read below,  even when you buy a diamond with a certificate, it is still a diamond that was graded by an individual with a subjective range of standards.

 The 4 C’s


One of the first things they teach in diamond school is that when judging the color of a diamond you must – I repeat must – use a master set. In other words, while an appraiser can estimate the color of a stone on a white piece of paper, the only way to truly judge a stone’s color is to compare it to another stone that has already been graded.

Why? Because the color grade of a diamond is not absolute, it is a range. A grader takes a diamond and first “guesses” by looking at it face up and face down in a small white paper dish.  Once a “guesstimate” is made, the stone is taken to a master set that has a sample diamond representing colorless “D” through light yellow “M”. The grader has to decide which color most closely matches the master set. So while two diamonds might be assigned a “G” or near colorless, one stone might be closer to “F” or what I call a “G+” while the other is closer to “H” what I call a “G-“… yet both would be graded a “G” by the GIA method.


The clarity of a stone is also subjective. When discussing clarity we are talking about the inclusions also known as visible “flaws” in a diamond.  Most diamonds I buy for clients are in the VS (Very Slight) or SI (Slightly Included) range. So what is the difference? Well for both stones it would be very difficult to see an inclusion with the naked eye. The GIA standard is to grade a diamond using a microscope with no more than 10x magnification. 

A diamond grader looking at a stone that is SI means that it is slightly include and a trained eye can find the inclusions quickly. My instructor at the GIA gave us four simple buzzwords to help us categorize inclusions for clarity grading. Minute inclusions would grade a stone VVS (very very slightly). Minor inclusions VS (very slightly). Noticeable inclusions SI(slightly included), and finally, when inclusions are obvious the stone is graded in the I range for included.

And there’s more. For each category, as a grader, we must decide if the stone is VVS1 or VVS2 – in other words very very slightly included or a bit more very very slightly included.

 Cut This is a more definite calculation and is probably the most undervalued “C” by consumers, yet for dealers and buyers, next to color, the most important for sale-ability of a stone. The cut of a diamond gives it its scintillation or its “sparkle”.  A diamond with an EX or excellent cut will have more sparkle than a diamond with VG or very good. Diamonds rated G for good and F for fair are what is used in most retail, online and commercial goods. Most fine jewelry uses EX or VG cut diamonds.

Before I took my diamond lab class at the GIA, like many consumers, when comparing diamonds I looked at two of the 4c's - color and clarity. 

And then I looped and compared hundreds of diamonds.  And a funny thing happened. I had just graded a G VVS diamond with a "good" rating for the "make" or finished cut of the stone. Then, just after, I graded a G SI2 diamond with an "excellent" rating for the "make" or finished cut of the stone.

While the clarity - or amount of visible inclusions under a loop was far better in the first stone/VVS - the scintillation or "sparkle" or the second/SI was far better - and would definitely be the stone I would prefer to own and wear.

And guess what? There is a huge difference in price - a G VS being far more expensive.

Simply put this is the weight of a diamond. Usually it will be abbreviated on a sales ticket. TW or CTW when adding the weight of all the diamonds in a setting.

List of Common Diamond Rating Agencies:

  • Gemological Institute of America (GIA)
  • American Gemological Society (AGS)
  • European Gemological Laboratory (EGL)
  • International Gemological Institute (IGI)

Thank you for reading my blog, and as always, feel free to contact me if you have any questions.

all photos from the GIA website.


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