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American Gem Society Laboratories (AGS)

The American Gem Society (AGS) Diamond Grading Laboratory uses a cut grade system that assigns diamonds a cut grade as a number between 0 and 10. The AGS Cut Grade reflects the impact of 3 key elements on a diamonds beauty and value

Polish refers to the diamond's surface quality, including the presence or absence of characteristics such as abrasions, scratches, nicks and polishing marks.
Symmetry is the balance and evenness of faceting and is a measurement of manufacuring accuracy. Facets are comapred as opposing pairs.
Proportions are the sizes and angles of the diamond's overall parts.

The AGS Ideal 0 cut grade represents the best in diamond cutting.

AGS 0 is only assigned to a diamond in which correct proportions for Ideal, precise symmetry and fine polish are combined to produce an optimum display of brilliance, scintillation and dispersion. It represents a balance between the physical dimensions of the diamond and the optical components of its beauty.

As diamonds fall into grades further from O (ideal), their relationship to beauty tends to diminish. A diamond with a cut grade of 1 or 2 (very fine cut) are very similar in appearance. A cut grade 5 diamond has variations that detract significantly from overall appeal. It may appear 'washed out' or dark through the center. Cut grades 10 are the worst examples of proportioning, symmetry and polish and have little life, fire or scintillation.

There are five principle factors to consider in evaluating proportions:

The Tables below show AGS cut grades 0 (Ideal), AGS grade 1 (Ex Fine) and 2 (Very Fine) for various proportions. These tables are not definitive, but should provide a reasonable interpretation of the AGS standards.

To evaluate a diamond's proportions, we measure each factor, one at a time, and assign it's appropriate grade using the proportions grade charts shown. The lowest of the five grades (the highest number) will be the diamonds overall proportion grade. To receive a grade 0, diamonds must fit the parimeters shown for 0 in all five categories. 

Average Crown Depth/Angle
% Depth Angle AGS Cut Grade
11.7   28.3 Less 10
11.8 12.1 28.4 29.1 9
12.2 12.4 29.2 29.6 8
12.5 12.6 29.7 30.1 7
12.7 12.9 30.2 30.6 6
13.0 13.1 30.7 31.1 5
13.2 13.4 31.2 31.6 4
13.5 13.7 31.7 32.1 3
13.8 13.9 32.2 32.6 2
13.9 14.5 32.7 33.6 1
14.6 15.7 33.7 35.8 0
15.8 16.0 35.9 36.3 1
16.1 16.3 36.4 36.8 2
16.4 16.6 36.9 37.3 3
16.7 16.9 37.4 37.8 4
17.0 17.2 37.9 38.3 5
17.3 17.5 38.4 38.8 6
17.6 17.8 38.9 39.3 7
17.9 18.1 39.4 39.8 8
18.2 + 39.9 + 9
Average Pavilion Depth/Angle
% Depth Angle AGS Cut Grade
39.4 Less 38.3   10
39.6 40.1 38.4 38.7 8
40.2 40.6 38.8 39.1 7
40.7 41.1 39.2 39.4 5
41.2 41.6 39.5 39.8 4
41.7 42.1 39.9 40.1 2
42.2 43.8 40.2 41.2 0
43.9 44.3 41.3 41.5 1
44.4 44.8 41.6 41.8 2
44.9 45.3 41.9 42.2 4
45.4 45.8 42.3 42.5 5
45.9 46.3 42.6 42.8 6
46.4 46.8 42.9 43.1 7
46.9 47.5 43.2 43.5 8
47.6 48.5 43.6 44.1 7
48.6 + 44.2   10
Average Table Diameter %
% Diameter   AGS Cut Grade
46.3 & Less   10
46.4 47.3 9
47.4 48.3 8
48.4 49.3 7
49.4 50.3 5
50.4 51.3 3
51.4 52.3 1
52.4 57.5 0
57.6 59.5 1
59.6 62.0 2
62.1 63.5 3
63.6 65.5 4
65.6 67.5 5
67.6 69.5 6
69.6 71.5 7
71.6 73.5 8
73.6 75.5 9
75.6 + 10
Girdle - Culet - polish/Sym
Girdle AGS
Ext Thin 3
V Thin 1
Thin, Medium 0
Sl Thick,Thick 2
V Thick 5
Ex Thick 7-10
   
Culet Size  
None, V Small 0
Sm, Med, Sl Large 1
Large 3
V Large 5
Ex Large 7,8,9,10
   
Polish- Symmetry
Characteristics
AGS
Ex Difficult 10X 0
V Difficult 10X 1
Difficult 10X 2
Easy 10X 3
V Easy 10X 4
Obvious 10X 5
Unaided Eye 6
Easy 7
Obvious 8,9,10

Example
A diamond wtith the following proportions would attract a cut grade of 1.

Crown Angle: 34 Degrees (0)
Pavilion Angle: 41 Degrees (0)
Table Diameter: 57% (0)
Girdle: Very Thin (1)
Culet: Very Small (0)
Polish: Excellent / Extremely Difficult to see defects with 10X lens (0)
Symmetry: Excellent / Extremely Difficult to see defects with 10X lens (0)

If we add up each component the result is 0+0+0+1+0+0+0= 1 which would represent the AGS cut grade AGS1.
If the girdle had been medium, the result would have been AGS0.

Select a diamond that is cut grade 0 (ideal) or cut grade 1 (ex fine) or 2 (very fine). If you desire a cut grade 0 (ideal cut), it will usually cost 15 to 20% more than diamonds with the same color and clarity grades but with lesser cut grades eg. 1 or 2 or 3. The added cost you pay for a 0 grade (ideal) is a result of the additional manufacturing time the cutter works when finishing a diamond to exact tolerances and the small supply of 0 grade (ideal) diamonds that are available. AGS 0 grade (ideal) diamonds are difficult to source.

 

 
 
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