Basic Diamond Shapes
For a Round Brilliant Cut, there is a balance between brilliance and “fire”. A diamond cut for too much “fire” looks like a cubic zirconia, which gives out much more “fire” than a real diamond. A well executed round brilliant cut should reflect the most light out from the tabletop and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows.
In the past, the “Cut” quality of the “4 C’s” was the most difficult part for a consumer to understand when selecting a good diamond because a GIA or AGS certificate did not show the important measurements influencing cut (i.e. pavilion and crown angle) and did not provide a subjective ranking of how good the cut was. Only a trained eye could see the quality of a good cut. All of that has changed with the new GIA “Cut Grading System”.
The proportion and symmetry of the cuts as well as the quality of the polish are factors in determining the overall quality of the cut. A poorly cut diamond with facets cut just a few degrees from optimal will result in a stone that lacks the gem quality because the “brilliance” and “fire” of a diamond largely depends on the angle of the facets in relation to each other. An Ideal Cut or Premium Cut “Round Brilliant” diamond has the following basic proportions:
* Table Size: 53% to 60% of the diameter,
* Depth: 58% to 63% of diameter,
* Crown Angle: 34 to 35 degrees,
* Girdle Thickness: medium to slightly thick,
* Facets: 58 (57 if the culet is excluded),
* Polish & Symmetry: very good to excellent,
Basic Diamond Shapes
The shape of the cut is a matter of personal taste and preference. However, the quality of the cutter’s execution of that shape is of primary importance. The shape of the diamond cut is heavily dependent upon the original shape of the rough stone. The round brilliant cut is preferred when the crystal is an octahedron, as two stones could be cut from one crystal. Asymmetrical raw crystals are usually cut in a “Fancy” style. Several basic diamond shapes (Fig. 2) are listed below.
The “Round Brilliant” cut was introduced in the middle of the seventeenth century. The first Brilliants were known as Mazarins, and had only 17 facets on the crown. In the early 1900′s the 58 facet modern Round Brilliant was developed (Fig. 2 far right below).