The Quality of the cut is the most important factor in determining how well the diamond will sparkle.
| If the cut is too shallow, light escapes through the pavilion before it can be refracted. | If the cut of the diamond is too deep, some light escapes through the opposite side of the pavilion. | When a diamond is cut to good proportions, light is refracted from one facet to another and then dispersed through the top of the stone. |
The two prime factors in assessing quality of cut are depth and table.
Depth affects the amount of light reflected back to a viewer's eye. If a stone is too shallow, the light will pass right through it; if it's too deep, the light gets lost.
Table and symmetry are also very helpful to ensure the proper sparkle in your diamond. Polish refers to the overall finish of the diamond. A diamond with poor polish looks like looking into a foggy windshield. The symmetry of a diamond is based on how well the facets of your diamond match up. Referring to the diagram below, the "Pavilion facet" should line up with the "Bezel facet." All bezel, star, upper, lower, and pavilion facets should be the same size. When symmetry falls under the "Very good" or "Excellent" ranges, your diamond will have the best fire and brilliance.
| Cut | Preferred | Too Long | Too Short |
| Emerald | 1.50-1.75:1 | >2.00:1 | 1.10-1.25:1 |
| Heart | 1.00:1 | >1.25:1 | <1.00:1 |
| Triangle | 1.00:1 | >1.25:1 | <1.00:1 |
| Marquise | 1.75-2.25:1 | >2.50:1 | <1.50:1 |
| Oval | 1.33-1.66:1 | >1.75:1 | 1.10-1.25:1 |
| Pear | 1.50-1.75:1 | >2.00:1 | <1.50:1 |
| Princess | 1:1 | >1.50:1 | <0.75:1 |
