Diamond Cut - AGS

AGS Cut Grade

The AGS Performance-Based Cut Grading System takes advantage of revolutionary hardware and software in considering a diamond’s performance.

The diamonds are first measured using a computerized measuring device, which also creates a three-dimensional model. The diamond grader imports the information into the AGS ray-tracing software and receives values for proportions and light performance. The diamond grader then analyzes the girdle, the culet, the symmetry, and the polish characteristics of the diamond.

From this the three elements of the final Cut Grade - Light Performance, Proportion, and Finish are assessed. The result is a more thoroughly analyzed diamond, which in turn helps to make a more informed buying decision.

As an indication of the level of thoroughness of the AGS Performance-Based Cut Grade, the following 11 factors are assessed.

Light Performance Factors

Brightness: The amount of white light returned to the observer. A finely cut diamond appear to be bright in a broad range of lighting conditions - not just in a perfect lighting environment.

Dispersion (fire): The separation of white light into spectral colors. Finely cut diamonds will exhibit larger amounts of spectral colors (the fire of white light being broken into the colors of the rainbow) when illuminated by direct light sources.

Leakage: Areas that do not return light. Finely cut diamonds minimize the areas of light leakage.

Contrast: The light and dark patterns seen when observing a diamond. It can produce a positive or negative optical effect. This usually is caused by, but not limited to, the observer’s head. Finely cut diamonds have enough contrast to look interesting, but not so much that they impact the brightness of the diamond.
 

Proportion Factors

Girdle Thickness: The thickness of the diamond girdle as a percentage. Finely cut diamonds have neither excessively thick nor thin girdles.

Culet Size: The presence and size of a culet facet. The facet that is sometimes present at the ‘point’ of the diamond. Finely cut diamonds do not have excessively large culets.

Weight Ratio: The millimeter footprint of a diamond versus its weight. Finely cut diamonds lack excess weight. They achieve high performance without it.

Durability: The diamond’s resistance to chipping or breaking. Finely cut diamonds are resistant to chipping.

Tilt: The point at which the girdle reflects under the table of the diamond and is defined by the minimum pavilion angle allowed for each table size. Finely cut diamonds will not exhibit what is known as a "fish-eye effect" where the edge (girdle) of the diamond is reflected through to the viewer when viewed from a typical angle.
 

Finish Factors

Polish: The degree to which the facets of the diamond have been polished to remove surface imperfections. Finely cut diamonds lack polishing imperfections on their facets.

Symmetry: The degree to which the diamond is cut with symmetry between corresponding parts of the diamond. Finely cut diamonds are highly symmetrical and are precisely cut.

Download our Diamond Grading Sheet file (pdf format)

Assessing the AGS Grade

The final grade is assessed based on these eleven factors. A very intuitive, number grade between 0 and 10 is assigned to the diamond, based on whether it matches the Ideal parameters (cut grade 0), or how far from those parameters it lies.

The grading scale:

• 0 - Ideal: Superior craftsmanship in the diamond cutting process. All cut quality factors are at the highest possible levels, and they make the maximum contribution to the diamond’s beauty and value.
• 1 - Excellent: Very slight variations in one or more of the diamond cut quality factors, but these can be detected only by computer analysis.
• 2- Very Good: Slight variations in one or more diamond cut quality factors that can be detected by computer analysis.
• 3 and 4- Good: Minor variations in one or more diamond cut quality factors can be detected by computer analysis. These variations may have a slight effect on the diamond’s beauty, durability, or size appearance. Some differences in appearance may be noticed in careful side-by-side comparisons made with diamonds of higher cut grades.
• 5 to 7 - Fair: Sizable variations in one or more diamond cut quality factors can be detected by computer analysis. These variations have little effect (in grade 5) to a noticeable effect (in grade 7) on the diamond’s beauty, durability, or size appearance. Diamonds in these cut grades have diminished light performance when compared with diamonds in higher cut grades.
• 8 to 10 - Poor: Major variations in one or more diamond cut quality factors have significant (8) to serious (10) negative effects on the diamond’s beauty, durability, or size appearance. Noticeable poor light performance characterizes diamonds in these cut grades.

The Angular Spectrum Evaluation Tool — ASET

The Angular Spectrum Evaluation Tool (ASET), is our tool that easily allows the light performance of diamonds to be evaluated. The tool mirrors the work performed by the AGS  in the cut grading methodology.

A diamond can be viewed with color-coded regions that show from angle the light enetered the diamond.

• Light entering from directly above is coded blue
• Light entering from the mid angle (45—75 degrees) is coded red
• Light entering from a low angle (below 45 degrees) is coded green
• Light leakage is coded by white

A finely cut diamond gathers a majority of light from the mid angle, and will show a great deal of red color when viewed in the ASET. The low angle light performs poorly for returning light, and is minimized in the ideal cut diamond. Contrast in the diamond is seen in a pattern of darker areas produced by the person viewing the diamond. This is seen in the distinctive arrow pattern shown in blue.

The image shown here is but one example of the patterns that ideal cut diamonds produce. The one pattern from one ideal cut diamond to the next will vary.