One of the most important factors in determining quality in diamonds is the cut. Diamond cut is the only value factor that is a result of human skill. It is thus essential that you be well advised of the quality of the cut when purchasing a diamond.
The brilliant sparkle of a diamond comes from the finishing and proportioning of the stone.
Finish
Includes polish and symmetry:
Polish
Describes the condition of the surface of the stone and include blemishes that are not serious enough to affect the clarity grade.
Symmetry
Centered table or culet, regular shape of the table, round girdle, parallel girdle and table, pointing facets, aligned between the crown and pavilion.
Proportion
Gemologists agree that the best diamond cut is the one that follow a set of formulas calculated to maximize brilliance. These formulas can be seen in a diamond's proportions, most importantly how the depth compares to the diameter, and how the diameter of the table compares to the diameter of the diamond. The important proportions are:
- Table (the largest facet at the top) size
- Crown (the top part from the girdle to the table) height and angle (angle of the bezel facets with the girdle)
- Pavilion (the bottom part from the girdle to the culet ) depth and angle (angle of the pavilion facets with the girdle)
- Girdle (the narrow band around the widest part of a diamond) thickness
- Culet (the facet at the bottom tip) size. The preferred culet is not visible to the naked eye (graded small or none)
If the finishing and proportioning are at their best, the parameters that create the optical beauty of a diamond will reach their optimum state.
- Luster
- The quantity and quality of light reflecting from the surfaces of a diamond.
- Brilliance
- The amount of white light returned to the eye from the diamond.
- Dispersion
- The amount of rainbow colors returned to the eye from within the diamond.
- Scintillation
- The sparkle, which is the combination luster, brilliance, and dispersion when there is movement by the wearer or light source.
Most diamonds are cut round with a full 58 facets. The angles of the cuts create prisms and reflective surfaces. When a diamond is well-cut, light enters through the table and travels to the pavilion where it reflects from one side to the other before reflecting back out of the diamond through the table and to the observer's eye. This light is the brilliance a good cut has a spectacular flashing, fiery effect.
A Diamond's Main Types of Cut
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Here are the main types of diamond cut and their effects on diamonds' appearance:
Ideal Cut
A diamond cut to optimal proportions, with optimal polish and symmetry to produce maximum brilliance, dispersion, and scintillation. Diamonds cut to this standard are the most valuable as they are produced with the most weight loss (only about 5% of the round brilliant diamonds on the market are cut to this standard). It is the cut that enables a diamond to make the best use of light.
Well-Cut
Diamonds that have very good optical beauty.
The parameters are slightly different from the parameters of Ideal Cut diamond.
These diamonds are priced less than Ideal cuts because they are not as rare.
Deep Cut
This cut creates the illusion of a smaller stone than it actually weights because it is cut with a deep pavilion (bottom of the diamond) that does not reflect light back through the crown (top of the diamond). Light leaks out the pavilion producing a dark appearing diamond that lacks beauty. These diamonds are sometimes called nailheads due to their dark appearance.
Shallow Cut
Diamonds that are cut with shallow pavilions that do not reflect light back through their crown. The effect is that of a larger stone. The light leaks out from the pavilion, producing a watery appearance. These diamonds are sometimes called fisheyes, due to the dull appearance and the lack of brilliance.
Bow-Tie
It is an effect of a dark area in the center of some fancy-shaped diamonds. A bow-tie effect retracts from beauty and lowers the value of a diamond.
The ideal cut with correct proportions and angles will give a diamond the maximum amount of light reflection, refraction and sparkle. It maximizes the brilliance, fire and beauty. As diamond angles and proportion deviate from ideal ones, fire is reduced, although the diamond may still be quite brilliant. Even if a diamond has good color and good clarity its value could suffer if it has a poorly proportioned cut.
Many jewelers will not discuss cut proportions unless the customer specifically asks; a stone rich in carat weight but poorly proportioned can be deeply discounted giving the buyer a false impression of a great deal.
Beware: Sometimes cuts are described using different terms such as commercial cut. This is nothing but a cut made for commercial purposes, usually to deceive the eye. It is graded under the average cut.
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