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Home >> Diamond Grading >> Diamond Shapes >> Diamond Cut >> Ideal Cut >> AGS Guidelines

History of the Ideal Cut: The earliest guidelines for diamond fashioning were based more on aesthetics than science, but in 1900 the round brilliant had evolved into something very close to its current form. No formal work on the relationships between optics and diamond cutting appeared until the twentieth century. Then much later, in 1919, Marcel Tolkowsky -- a member of a Belgian cutting family -- published a short paper entitled Diamond Design. This was the first analysis of diamond cutting based on modern science theories of light behavior.

Although Diamond Design was first published in England, Tolkowsky’s design is often called the “American Ideal Cut” because US cutters were the first to produce it in significant quantities. In the e 1950’s, AGS adopted Tolkowsky’s model as its standard for grading cut.  The only modifications to the basic design were establishing limited ranges for table size, crown height, pavilion depth and girdle thickness.  In 1955, the updated model was renamed the AGS Ideal Cut.

The demand for AGS Ideal has increased substantially and today numerous cutters around the world are producing designs loosely referred to as “Ideal Cuts.” The standards for these “ideals” vary significantly, and as a result, the ability to recognize and evaluate diamond cutting variations is even more important than it was a decade ago. The popularity of “ideal cuts” and the increased consumer demand for verification of this quality factor were among the primary reasons for establishing the AGS Laboratory . Opened in 1995, the lab has grown quickly because it is the only US facility that addresses cut grading in diamond in Diamond Quality Documents.  (GIA Gem Trade Laboratory), the primary industry source for diamond quality documentation does not address the issue of cut grade in its reports.

American Gem Society (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

  • proportions
  • symmetry
  • polish

Proportions are the sizes and angles of the diamond’s main parts. Symmetry is the balance and evenness of its faceting and shape. Polish refers to the diamond’s surface quality, including the presence or absence of characteristics such as abrasions, scratches, nicks and polish wheel lines

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

AGS 0 is only assigned to a diamond in which correct proportions, precise symmetry and fine polish are combined to produce an optimum display of brilliance, scintillation and dispersion. The impression is a harmonious 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 begins to diminish. For example, a diamond with a cut grade of 1 or 2 (very fine cut) are very close to 0 in appearance. A cut grade 5 diamond has variations that detract significantly from overall appeal. It may appear somewhat “washed out” or slightly dark through the center. Cut grades 10 are the worst examples of proportioning, symmetry and polish; so they have little visual “life.”

There are five factors to consider in evaluation proportions:

  • Table Size
  • Crown Angle
  • Girdle Thickness
  • Pavilion Depth%
  • Culet Size

Diagram shows AGS cut grade 0 (ideal), AGS grade 1 and 2 (very fine) Highlighted in Gray

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

We suggest selecting a diamond that is cut grade 0 (ideal) or cut grade 1 or 2 (very fine). If you desire a cut grade 0 (ideal cut), it will usually cost 10 to 15% more than most diamonds with the same color and clarity grades with cut grades 1 or 2 (very fine) The added cost you pay for a 0 grade (ideal) is a result of the additional manufacturing time the cutter is forced to expend when finishing a diamond to exact tolerances and the small supply of 0 grade (ideal) diamonds that are available. AGS 0 grade (ideal) diamonds in large sizes and high qualities over 1 1/2 carats in size are difficult to find in the market today.

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