Cutting a Diamond
When polishing a rough diamond, cutters must strike a balance between achieving an ideal cut (which provides exceptional appearance) and maximizing carat weight. Due to market demand, many customers lean towards larger diamonds with fair cuts over slightly smaller diamonds with superior cuts. This preference often pressures cutters to prioritize weight over appearance.
Determining Depth
Diamond depth is a key element of a diamond’s cut. It is the height (in millimeters) measured from the culet (the bottom tip) to the table (the flat, top surface). On a grading report, depth is typically represented in two forms. The first is the actual depth in millimeters, while the second is the depth percentage, which compares the diamond’s depth to its width. This percentage is calculated by dividing the total depth by the average diameter and multiplying by 100.
Light and Depth
Once light enters a diamond, the diamond’s depth dictates the amount of light that reflects back to the observer’s eye. If the depth is too shallow, light hits the pavilion facet at a low angle and exits through the bottom, causing light leakage. Conversely, if the depth is too deep, light reflects off the first pavilion facet, hits the second at a low angle, and escapes through the bottom. An ideal diamond depth, however, allows light to strike the pavilion facets at angles that reflect most light back to the top, enhancing brilliance.
Table and Depth
Both diamond depth and table are essential in crafting a stunning diamond. The table is the flat facet on the diamond’s surface visible when viewed face-up. As the largest facet, the table is crucial for brilliance, as it refracts incoming light rays and reflects them back into the observer’s eye.
Diamond Table and Depth
| Shape | Ideal Table % | Depth % |
|---|---|---|
| Round | 53-58 | 59-62.3 |
| Oval | 53-63 | 58-62 |
| Emerald | 61-69 | 61-67 |
| Princess | 67-72 | 64-75 |
| Asscher | 61-69 | 61-67 |
| Pear | 53-63 | 58-62 |
| Marquise | 53-63 | 58-62 |
| Radiant | 61-69 | 61-67 |
| Cushion | 61-67 | 61-67 |
| Heart | 53-63 | 58-62 |
Table Percentage
Akin to depth percentage, the table percentage of a diamond is determined by dividing the table’s diameter by the average diameter of the girdle. For fancy-shaped diamonds, this percentage is derived by dividing the table width by the widest part of the stone.
Ideal Round Diamonds
The ideal table and depth percentages can vary based on the diamond shape. For instance, the optimal depth for round diamonds ranges from 59.5% to 62.9%, while the ideal table percentage lies between 56% and 63%. For princess-cut diamonds, the depth ranges between 64% and 75%, with a table percentage between 67% and 72%. Oval diamonds’ ideal depth falls between 58% and 62%, with a table percentage between 53% and 63%.
Diamond Cut Grading
The cut grade of a diamond is influenced by both table and depth. Among the 4 Cs of diamonds, cut is the most intricate and technically demanding to evaluate. Laboratories assess cut by calculating the facets’ proportions affecting the diamond’s face-up appearance, analyzing how the diamond interacts with light to produce brightness, fire, and scintillation—all critical to the diamond’s brilliance. Cut grade also accounts for the diamond’s design and craftsmanship, including its weight relative to its diameter, girdle thickness, symmetry, and polish quality.
Based on these attributes, the diamond’s cut is graded on a scale that varies by laboratory. The Gemological Institute of America (GIA) and European Gemological Laboratory (EGL) use a scale of Excellent, Very Good, Good, Fair, and Poor. Meanwhile, the American Gem Society (AGS) employs a numerical scale from zero to ten.
Given that cut significantly impacts a diamond’s overall quality, it serves as an excellent starting point when selecting the perfect diamond. Thoroughly researching the ideal cut for your desired diamond shape is essential.
