Diamond Cut Quality

Diamond Cut (Precision)
Visual Performance is Controlled by Cut Precision
Cut Precision = Polish, Symmetry, Proportions
“SHAPE” is not the same as “CUT”

When a diamond comes out of the ground it looks like a shiny pebble or piece of quartz. In fact, it is so unimpressive that it would be amazing if you actually recognized it as a diamond. The first diamond discovered in South Africa (not the world) was found in 1866 when a young shepherd named Klonkie hurled it at one of his friends, Erasmus Jacobs, who pocketed it and gave it to his sister to play with. Quite some time later, a visitor to the Jacobs home commented that the shiny pebble might be a diamond. Eventually, it was confirmed as being a diamond weighing 21.25 carats and was cut into what is now the 10.73 carat oval brilliant Eureka Diamond.

Precision cutting is necessary to release the beauty of a diamond. The brilliance, fire, and scintillation that make diamonds so desirable is the result of how skillfully a diamond is cut. With this in mind, it’s time for you to realize that Cut is the most important, and least understood, factor of the 4C’s.

Lay people often confuse the SHAPE of a diamond with its CUT, this is most likely due to the industry’s synonymous use of the terms “cut” and “shape” to describe a diamonds shape (outline), i.e. marquise cut, round brilliant cut, princess cut, Asscher cut, or pear shape. In reality when we refer to the “cut” or “the make” of a diamond, we are really referring to a compilation of three factors which combine to determine the Overall Cut Grade of the diamond:

  1. Proportions, the angles of the facets described in degrees and percentages.
  2. Polish, the finish quality of the diamond.
  3. Symmetry, the consistency of facet shape and alignment.

If you remember only one thing from this site, remember this…

98% of a diamond’s visual performance (brilliance, dispersion, scintillation) is controlled by the quality of its cut, not its clarity, color, or size… but rather, it’s proportions, polish, and the symmetry of its facets. The other 2% is in your head and generally represents your mistaking a brighter color such as D-E-F for brilliance because the diamond looks “whiter” in comparison to other diamonds which you might have seen that happen to be G-H-I or warmer in color. None of the other factors, Color, Clarity, or Carat weight, have a more dramatic effect on the beauty of a diamond than its Cut. Subtle and minute dimensional differences of a degree or so can determine whether a diamond will be full of life or dull and listless.

With that in mind, we’d like to introduce you to the concept of “Ideal Cut” diamonds. That is, diamonds cut within a specific range of “ideal proportions” that consistently deliver maximum brilliance, dispersion and scintillation. Just as you can reap the benefits of a great haircut, or look like a dork for six weeks, diamonds look their best when they have been cut to precise proportions. Diamonds cut to these precise proportions are called “Ideal Cut” and are certainly worth looking for, especially since you don’t have to look any further than the vendors represented on this web site.

Defining Ideal Aspirations:

Ali Baba & The 40 Thieves have stolen a box of micrometers and would lead you to believe that every round brilliant cut diamond is an “Ideal Cut Diamond”. Can you say camel dung?

Now we’re not saying that everybody in the jewelry industry is a thief, or a member of Ali Baba’s gang, but there seems to be a lot of people in the diamond industry who rely upon a much looser definition of the term “Ideal Cut” than we do. Some of the diamonds which we’ve seen offered to people as “ideal cut” have combinations of proportions which are laughable at best. Even the Tooth Fairy knows that a round brilliant cut diamond with a Table Diameter of 60% and a Total Depth of 60% is not an ideal cut diamond, especially when the polish and symmetry grades of the diamond are Good / Good. But since you probably haven’t been buying diamonds as long as the Tooth Fairy has been tinkering about we’re going to make sense of all the mumble jumble for you.

In your quest for perfection you might here terms bantered about like Signature Ideal, European Ideal, American Ideal, and 60/60 Ideal, and all of them don’t mean a thing without a defined set of parameters by which to compare them. We base our use of the term “Ideal Cut” upon the grading system developed and used by the American Gem Society Laboratory (AGSL) because we find it to be a reliable standard. Regardless of the term used to describe any diamond you might be offered, it is possible for you to compare the actual proportions of the diamond to the AGS defined standard for “ideal proportions” by simply obtaining a computerized proportions analysis of the diamond in Sarin, OGI or Helium format.

The original Cut scale developed by the AGS consists of eleven categories which are used to describe the proportions of a round brilliant cut diamond, the highest rating is AGS Ideal-0 and the lowest is AGS-10 Poor. The overall cut grade of the diamond is determined by taking all of the factors (4) which comprise of (1) PROPORTIONS; (2) POLISH; (3) SYMMETRY; and (4) LIGHT PERFORMANCE ratings for the diamond. A diamond that receives the AGS Ideal rating for all four categories of the AGS Cut Grade (proportions, polish, and symmetry) is formerly known as “AGS IDEAL-0”.

Note that in the early days of the AGS Laboratory, a diamond graded as having AGS Ideal 0 Polish, Symmetry and Proportions was often referred to within the diamond industry as “AGS-000” or “triple zero ideal cut” and this description is inaccurate because the AGS Laboratory also uses a numerical system to reference Clarity and Color and thus a true “triple zero” diamond on the AGS Grading Scale would be one that received an Overall Cut Grade of AGS Ideal 0 with a Clarity Grade of Flawless (0) and which had a Color Grade of D (0) thus if you’re working with somebody who refers to a diamond as “triple zero” then you know you might be dealing with somebody who doesn’t understand what they’re talking about and who is several years behind the times.

Regardless of the name, a Super Ideal Cut Diamond cut to the Center Realm of the specifications for the AGS zero ideal cut rating will make the hairs on a gnats posterior stand up and quiver… That’s a politically correct colloquialism for those of you who can’t handle the word “ass”.

To properly determine the proportions rating of a diamond, it is mandatory that you know the Table Diameter (%); the Crown Angle (in degrees) which is NOT the same as the crown height (%); the Pavilion Angle (in degrees) which is NOT the same as pavilion depth (%); the Girdle Thickness (%); and the Culet Size. For your convenience the broad spectrum parameters for the original AGS Ideal Cut proportions rating for round brilliant cut diamonds is as follows:

Table Diameter: 52.4 – 57.5%
Crown Angle: 33.7 – 35.8° degrees
Pavilion Angle: 40.15 – 41.20 degrees
Girdle Thickness: Thin, Medium, Slightly Thick
Culet Size: None, Pointed, Very Small, Small, or Medium

We want to clearly state that the range of proportions stated above represents the original specifications for the proportions grade which was available from the AGS Laboratory from 1996 through June of 2005. The new proportions grade which is used in conjunction with the Light Performance analysis is much more in-depth and too complicated to try and explain in a few paragraphs because a different range is used depending on the table diameter measurement of the diamond.

Note that the Total Depth % of the diamond is not taken into account. This is because it is the Crown & Pavilion angles that control most of the brilliance and thus the Total Depth is not as important a factor. Just the same, we prefer that the total depth of a round brilliant cut diamond be somewhere between 59.0% and 61.8% with the ceiling being around 62.5% in our opinion. Although it is not uncommon to find AGS Ideal Cut diamonds with total depths as deep as 63.5% we recommend that you avoid them like the plague because they are simply too deep! There is a direct relationship between the outside diameter and the total depth of a diamond. The deeper the total depth, the smaller the outside diameter of the diamond will be for a specific range of carat weight. For instance, a properly cut 1.00 carat round brilliant ideal cut diamond should have an outside diameter in the range of 6.50 mm with a slight variance such as 6.49 – 6.53 mm or thereabouts. If the diamond had a deep total depth, such as 63.5% then the outside diameter might be more like 6.3 mm in which case you might be paying a one carat price for the look of a diamond which “faces up” like a 0.90 carat diamond. While the diamond might be vibrant and full of life, the fact is that there is a price increase that occurs between the 0.99 – 1.00 carat marks so it’s just bad business to pay a one carat price for the look of a ninety pointer. The concept holds true for diamonds in other weight categories, diamond prices increase based upon Price Per Carat (PPC) at various junctures of weight.

Proportion information for round brilliant cut diamonds is provided on AGS Diamond Quality Documents and GIA Diamond Grading Reports in the form of a diamond graphic which is a scale model of the diamond represented by the diamond grading report which is based upon the actual measurements of the diamond. Although the crown and pavilion angle measurements are provided on the lab reports, we do not rely on these measurements to judge the cut quality of the diamond because they represent the average measurements for the crown and pavilion angles.

It is important to review a Sarin, OGI, or Helium, computerized proportions analysis which divulges what the spread of the high and low measurements are for each section that comprises the average measurement indicated on the lab report. Think about it. If the average crown angle measurement indicated on the lab report is 34.5 degrees and the lowest crown angle measurement is 34.3 degrees and the highest is 34.8 degrees, that is great! But if the low measurement is 33.5 degrees and the high measurement is 35.5 degrees, that is less than desirable (okay, it sucks) but the average measurement indicated on the graph provided on the lab report would still be 34.5 degrees.

“Tolkowsky Cut” and “Tolkowsky Range”

The next trick that Ali Baba and his den of thieves likes to rely upon is the infamous Tale of Marcel Tolkowsky. A physicist and member of a Belgian diamond cutting family, who in 1919 published Diamond Design, the first analysis of diamond proportions. His work was based on [what were then] modern theories of light behavior and his opinion of what proportions resulted in the best possible balance of brilliance and dispersion of light.

Ali Baba likes to say things like “This diamond has Tolkowsky proportions, but I didn’t want to increase the price of the diamond by having it certified”. This is usually bunk, if all of the proportions for the diamond met Tolkowsky’s parameters, he would have sent it in to be lab graded because then he would be able to get a better price for the diamond. By the way, none of the independent gemological laboratories actually “certify” anything, they merely report the characteristics of the diamond based on their opinion at the time the diamond was graded; thus use of the term “certified” is erroneous and misleading at best.

Tolkowsky’s calculations for the ideal angles and proportions for a round brilliant cut diamond are as follows:

Table Width 53%
Total Depth 59.3%
Crown Angle 16.2% or 34° Degrees
Pavilion Depth 43.1% or 40.9°
Girdle Edge Extremely Thin – Knife Edge

Notice that Tolkowsky specified that the girdle edge of the diamond be “Knife Edge” or virtually non-existent. It’s great in theory, however many a girdle edge has been chipped because it was extremely thin and could not withstand the pressure of being set. Interestingly enough, a knife edge girdle would result in a rating of AGS-10 Poor on the AGS Proportions Scale. Perhaps this is why we have yet to see a diamond that is cut to Marcel Tolkowsky’s true standards. Instead what we see are a lot of diamonds cut within “tolerance of Tolkowsky’s standards” or “Tolkowsky Range”.

Using Sarin DiaMension computerized proportions analysis, we have evaluated a variety of “Tolkowsky Cut” diamonds with more realistic girdle measurements and have determined that the proportions of the diamond can range from AGS Ideal 0 to AGS-2 Very Good. Therefore, we recommend you only consider a “Tolkowsky Cut” diamond when you have all of the information required to determine the actual proportions of the diamond. We feel that the parameters of the current AGS Ideal Cut rating system are far more accurate than what Tolkowsky created on his chalkboard seventy years ago.

We have carefully hand selected a group of vendors who specialize in round brilliant ideal cut diamonds with proportions that can be verified as falling within the range of the zero ideal cut. If you’re looking for something truly spectacular and want to exceed the bragging rights of a both an “Ideal Cut Diamond” and a “Tolkowsky Cut Diamond” then we recommend you select one of the Hearts & Arrows puppies and present the diamond to your fiancé unmounted with a creative little ditty about how each of the eight hearts represents a special way you feel about her.

Although our primary focus is restricted to Ideal Cut Diamonds, we thought that you might find the parameters for the original AGS-1 Excellent through AGS-3 Good range of interest. The average light return for a diamond with AGS Ideal Polish, Symmetry and Proportions is around 96%. The average light return for a diamond with AGS-4 Good Polish, Symmetry and Proportions is somewhere around 70% which might help you to understand why we prefer ideal cut diamonds.

AGS-1 Excellent Proportions

Table Width – % 51.4 – 52.3% -or- 57.6 – 59.5%
Crown Angle – Degrees 32.7° – 33.6° -or- 35.9° – 36.3°
Pavilion Depth – % 43.9 – 44.3%
Girdle Thickness Very Thin
Culet Size Slightly Large

AGS-2 Very Good Proportions

Table Width – % 59.6 – 61.5%
Crown Angle – Degrees 32.2° – 32.6° -or- 36.4° – 36.8°
Pavilion Depth – % 41.7 – 42.1% -or- 44.4 – 44.8%
Girdle Thickness Very Thin to Slightly Thick
Culet Size Slightly Large or Smaller

AGS-3 Good Proportions

Table Width – % 50.4 – 51.3% -or- 61.6 – 63.5%
Crown Angle – Degrees 31.7° – 32.1° -or- 36.9° – 37.3°
Pavilion Depth – % 41.7 – 42.1% -or- 44.4 – 44.8%
Girdle Thickness Thick
Culet Size Large

Unless you’re comparing diamonds graded by a laboratory, it might not be easy for you to determine the actual proportions or cut rating of a diamond. Most diamond dealers and jewelry store owners actually don’t calculate the proportions of the diamonds that they buy and sell. They select them based on how brilliant they look and price them accordingly. If a diamond looks dull and lifeless, an experienced diamond grader knows that it’s poorly cut. The diamond will sell easily to an inexperienced buyer who only considers size, clarity, color and price when shopping for a diamond. A lot of companies on the net rely heavily on this fact, hence the abundance of on-line diamond search engines and long inventory lists of diamonds for sale. Ever notice how the crown angles and pavilion depth measurements are seldom listed for you to compare? Not to worry, this information is readily available from the select group of vendors we work with and we are happy to assist you narrow down the field of options by lending you a professional eye and years of expertise.

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