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Making the Grade

Most people call a diamond's shape "cut." Since January 2006, however, the Gemological Institute of America (GIA) started using the term to refer to the quality of a round polished diamond's workmanship, known as Cut Grade. 

Cut Grade considers the workmanship in transforming a diamond from rough to polished. It is the only characteristic of a diamond determined by human action.

The cut grade deconstructs a round diamond's beauty into many specific and precise components, mainly taking into consideration the proportions of a diamond. It is the symmetry and polish of a diamond, however, and the combination of the quality of the three determines a diamond's Cut Grade.

Simply put, the better the diamond's proportions, the more light reflects out of it. In this regard, light is measured by three attributes:

  • Brilliance – the total light reflected from a diamond.
  • Fire – the dispersion of light into the colors of the spectrum.
  • Scintillation – the flashes of light, or sparkle, when a diamond is moved.

A Cut Above

This is possibly the toughest characteristic to measure or analyze, requiring scientific tools to perform. Cut Grade is determined from a combination of measured parameters and visual observations. Table Size, Pavilion Angle, Crown Angle, Lower Half Length, Star Length, Girdle Thickness, Culet Size and degree of painting and/or digging out are all measured. See the following graph, sourced from GIA, for what each of the terms measures. 

Components of a Brilliant Cut Polished Diamond. Source: GIA                                                          

 The Finish – the quality of the Polish and Symmetry – are measured and reported for fancy shape diamonds.

In previous articles, we delved into the physical attributes of a diamond, focusing on characteristics such as Irregularities and Carat. Our intention then was not to dive into all the fine details, but to bring awareness to it as part of the Crystal Clear philosophy. This is what we intend to do here as well.

As such, there are two main points to consider – the Cut Grade reporting scale and the impact it has on a diamond's value.

GIA's cut grading system is a deductive one in which a diamond's cumulative cut grade is determined by the lowest value for any one of several examined components. The lab reports the Cut Grade on a five-step scale:

Excellent ​To qualify for an excellent cut grade, both polish and symmetry must be very good or excellent
Very Good
​To qualify for a very good cut grade, both polish and symmetry must be at least good
Good​To qualify for a good cut grade, both polish and symmetry must be at least fair
​To qualify for a fair cut grade, both polish and symmetry must be at least fair
Poor​A poor cut grade is assigned when either polish or symmetry is poor

                                                                                                       Source: GIA 

In the best-case scenario, a diamond will be reported to be Triple Excellent (sometimes noted as Ex, Ex, Ex). That means it has Excellent Cut Grade, Excellent Symmetry and Excellent Polish. A Triple Excellent Diamond has the highest value and any other combination results in a decline in value, which is an important point in understanding diamonds' value.

Based on the analysis of round shape D color, IF clarity diamonds currently trading in the market, the decline in value from Triple Excellent (EX, EX, EX) is detailed in the following tables. In the first table, Polish and Symmetry are Excellent and the Cut Grade is Excellent, Very Good (VG) or Good (G): 

Grading Value
​G, EX, EX

                                                                                                       Source: GIA 

With all other diamond characteristics being identical, the value of a VG, EX, EX diamond is 7% lower than the value of an EX, EX, EX diamond. The value of a diamond whose grading report is G, EX, EX will be 25% lower than an EX, EX, EX diamond.

There are about 70 different Cut Grade/Symmetry/Proportion combinations and the same value breakdown exists for every one of them. When a diamond does not have an excellent grading at all, the value declines sharply: 

Grading Value
​G, G, G
​F, F, F
​P, P, P

A better polishing job that achieves the best proportions adds to the value of a diamond, and vice versa. As the Crystal Clear philosophy outlines the components of diamonds' value and how different characteristics influences value, all these characteristics are eventually combined to create an interplay. In the article on size it was stated that a larger diamond has a higher value.

So what happens when a polisher needs to choose between size and cut grade? This is the kind of dilemma that polishers face daily, because of the characteristics of a rough diamond. What should they choose a larger diamond with less than perfect proportions or a smaller diamond with perfect proportions?

This dilemma is especially acute if it means going above or below a size value jump. This is evident in cases where a polisher has to decide between polishing the rough diamond into a 1.01 carat, D color, IF clarity VG, VG, VG diamond or a 0.92 carat, D color, IF clarity EX, EX, EX diamond.

According to the table above, the Triple Excellent diamond retains 100% of the value while the VG, VG, VG diamond only 88% of the value. We also need to take into account the value of weight. As detailed in the article on Carat, the value of diamonds weighing 1.00-1.19 carats is 52% higher per carat than diamonds in the 0.90-0.99 carat size range.

Therefore, the impact of size on value is much stronger than cut. So if the polisher prefers a heavier diamond, the result is a higher value diamond, even if it results in a VG, VG, VG cut.

This is important to know. If a buyer with a set budget is looking for a round diamond that weighs about a carat, and prefers a better-proportioned diamond that reflects more light, a 0.99 carat EX, EX, EX diamond will cost less than a 1.01 VG, VG, VG diamond while the difference in size is not noticeable once set in a ring.

It is not the goal of this article to detail every possible Cut Grade combination, but to ensure that the public is aware of this component of value and highlight it as part of the Crystal Clear philosophy's drive for transparency. By being aware of this information, a buyer can make a well-informed decision when considering the value of a diamond, especially if considering a diamond as part of a wealth preservation belief. 

No one should act upon any opinion or information in this website without consulting a professional qualified advisor.

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