Ideal Cut Diamonds

Well... there is a lot of debate about what exactly is "ideal cut" but back in the beginning of the last century a gentleman by the name of Marcel Tolkowski (a mathematician) came up with what would be considered to be the "ideal" proportions for a diamond that would yield the maximum amount of "brilliance", "fire", and "scintillation". His calculations resulted in the following proportions.

Tolkowski Theoretical Brilliant

While a stone like this is certainly GORGEOUS, technologies and observations developed over the years has showed us that it doesn't have to "strictly" be at those tolerances to deliver the most light return. Hence today we have what is called today by the name "American Ideal Cut" which would embrace the following tolerances in proportions.

Modern American Ideal Brilliant

It is these proportions that the American Gem Society Laboratories has adopted into their now MOST popularized cut grading system.

How cut is properly graded

The AGS lab considers 5 factors of the above diagram to determine the diamonds proportion cut grade and grades the diamond on a scale, based on numbers, starting at "0" which is the best and going down to "10". The 5 factors that are considered are the...

table percentage
crown angles
pavilion depth
culet &
girdle

The following chart is a breakdown of what makes the stone the proportion cut grade that it is....

Ideal cut. Grade of "0"

crown angles	33.7° - 35.8°
pavilion depth	42.2 - 43.8%
table size	52.4 - 57.5%
culet	pointed or none, very small, small or medium
girdle	thin, medium or slightly thick

This is how strict it is. If the table on a diamond falls at 57.6% IT'S NOT AN IDEAL CUT. The only way to get this precise is with computerized equipment. The AGS is the ONLY Gem lab that not only provides their clients with this information but also grades the cut as well. In my own independent lab here at Good Old Gold, this is the cut grading system I use as well and also have the computerized equipment to properly analyze the cut of a diamond with as well as equipment to manually analyze the cut as well.

The following charts will be for reference and show the tolerances for each of the 5 aspects that go into determining the proportion cut grade. First is crown angles

Cut Grade	Crown Angle Tolerances
0	33.7-35.8
1	32.7-33.6 35.9-36.3
2	32.2-32.6 36.4-36.8
3	31.7-32.1 36.9-37.3
4	31.2-31.6 37.4-37.8
5	30.7-31.1 37.9-38.3
6	30.2-30.6 38.4-38.8
7	29.7-30.1 38.9-39.3
8	29.2-29.6 39.4-39.8
9	28.4-29.1
10	28.3 and less 39.9 and greater

Just some comments on crown angles. If you compare what the "acceptable" standards are for a round brilliant cut diamond are (30-37 degrees) you could have a cut grade of 7 (if the crown angles actually fell at exactly 30 degrees) and still have what's considered a sparkler PROVIDED THIS WAS THE ONLY FACTOR making it a 7. For example if a diamond had a table size of 57%, pavilion depth of 43%, culet none, girdle thin to medium and the crown angles were say 30.6 degrees, this one factor could cause the diamond to be a cut grade of 6 and wouldn't necessarily be terrible. Keep in mind though that a cut grade of 6 WILL be cheaper than a higher cut grade.

Here's the breakdown for pavilion depth and imho is the most critical factor for internal light return.

Cut grade

Pavilion Depth

0

42.2 - 43.8%

1

43.9 - 44.3%

2

41.7 - 42.1%
44.4 - 44.8%

3

heh... no 3 ?

4

41.2 - 41.6%
44.9 - 45.3%

5

40.7 - 41.1%
45.4 - 45.8%

6

45.9 - 46.3%

7

40.2 - 40.6%
46.4 -46.8%

8

39.5 - 40.1%
46.9 - 47.5%

9

47.6 - 48.5%

10

39.4% and less
48.6% and greater

Just some personal comments on pavilion. It is my strong opinion that this one factor alone can make or break a stone and if a person is considering diamonds that are not necessarily ideal cuts ... you still want to keep this factor no lower than a 2 on the cut scale. Sadly this most crucial information is lacking in some of the most popular reports. IF pavilion depth cannot be provided BUT the pavilion angles can be, to keep within acceptable standards stay with pavilion angles that do not fall out of the spectrum of 40-42°. I don't purchase unless I know one or the other ... preferably both. Any stone you consider with me, no matter what lab has looked at it you WILL know BOTH.

Now for the table size.

Cut grade	Table size
0	52.4 - 57.5%
1	51.4 - 52.3% 57.6 - 59.5%
2	59.6 - 61.5%
3	50.4 - 51.3% 61.6 - 63.5%
4	63.6 - 65.5%
5	49.4 - 50.3% 65.6 - 67.5%
6	67.6 - 69.5%
7	48.4 - 49.3% 69.6 - 71.5%
8	47.4 - 48.3% 71.6 - 73.5%
9	46.4 - 47.3% 73.6 - 75.5%
10	46.3% and smaller 75.6% and higher

Just some comments on the table size. It is RARE if I even find tables on diamonds, even ideal cut diamonds that are lower than 55%. A few scattered around maybe that are 53-54%. A table size that is more common on the market today are table sizes that are 60 - 63%. I generally don't recommend a table that is bigger than 64% which would allow down to a 4 on the cut scale for table size. A table in that 60-64% zone coupled with crown angles that fell on the shallower side on or around 30-33º WILL make a diamond look bigger than what it weighs and let's face it guys... woman like size :) Below is an example of such a stone. Notice the crown angles at 30.8 is what's making the stone it's proportion grade of 5 and the table at 61.6% would contribute to a cut grade of 3. Whatever the highest number is, that's the cut grade of the stone.

This is an example of a diamond that I really wouldn't have a problem recommending, so long as the individual wasn't necessarily looking for an "ideal cut" diamond but wanted a stone that would still have REALLY good brilliance. It's pavilion depth is right on at 43.1% and it's only slight deviations in the crown that affect the cut grade.

So to sum up this teaching on "Ideal Cut Diamonds" or AGS "0" proportion cut grade stones... it's quite simple. The lower the number, the higher the grade ... the more bucks you're going to shell out for the stone. What I usually recommend to all my clients is to at least keep within the "acceptable standards" for a round brilliant cut. At my place of business I put "0" cut grades next to ones of 1-4 and have had people go both ways. Some don't see much of a difference and purchase the lower cut grade (which still IS A JAMMIN STONE), and then some insist on the best and want to see nothing but ideal "0" cut grades.

Update 2000

The GIA has conducted studies on brilliancy in diamonds and have found that diamonds that fall out of the AGS0 have great or excellent light return and are very bright diamonds. There are certain combinations of table size, crown angles and pavilion angles that can either intensify or increase the brilliance of a diamond and there are also combinations that can severely reduce the beauty of the diamond. You can directly view these results through both the Firescope™ and the BrillianceScope™. 2 pieces of lab equipment I have that analyze the internal workings of diamonds, as opposed to it's external measurements alone. To understand more of this you'll have to read the upcoming chapter on the Firescope™ and the discoveries I've made with this that are just like what GIA has been stating in their studies.

Currently in the pricing of diamonds however, the most expensive diamonds are the ones rated on the AGS scale and is why I am teaching and familiarizing you with that cut scale. We may see things change in the near future based on information you'll find on this site, especially dealing with this very thing of the internal workings of the diamond. Another term which the president of AGS defines as Optical Symmetry. Read on... you're getting there. ;)

Well... just when you thought you've seen it all there are diamonds that go beyond even a "0" and are in a class all by themselves. Click on the "next" button to learn about the AGS "000".