Diamond cut is the most important of the four Cs, so it is essential to understand how the reflective quality of a diamond affects the value and properties of a diamond. A good cut will give the diamond its brilliance, which is the brightness that seems to come from the very heart of a diamond. Any diamond’s angles and finish determine its ability to handle light, which leads to brilliance.

(Please See Diamond Anatomy to explain the terms used in the following paragraphs.)

The images below show that light enters the table when a diamond is well-cut. It travels to the pavilion, reflecting from one side to the other before it reflects it from the diamond through the table and the eye of the observer. This light is the brilliance we mentioned, and this flashing, fiery effect makes diamonds so mesmerizing.

A poorly cut diamond has light moving through the table, reaching the facets, and then ‘leaking’ out from the bottom or sides of the diamond rather than reflecting the eye. Less light reflected to the eye means less brilliance.

Good Proportions Are Key

Most gemologists agree that the best-cut diamonds follow a set of formulae calculated to maximize their brilliance. These formulae can be seen in the diamond’s proportions, most notably how the depth compares to the diameter and how the table’s diameter compares to the diamond’s diameter.

If you opt to buy a diamond without an HRD or GIA certificate, spend some time looking at certified diamonds (where you know the Cut Grade) and train your eyes to identify the better cuts (by their “sparkle”). The cut makes a huge difference to the appearance of a stone.

The variance in the proportions between a poor diamond cut and an ideal Cut can be hard to tell apart from a casual observer.

Because cutting is so important, various grading methods have been developed to help buyers determine the cut of a particular diamond. In general, these grades are:

•         Ideal
•         Excellent
•         Very Good
•         Good
•         Fair & Poor

Which Grade Of Diamond Cut Should I Buy?

Selecting the grade of cut is a matter of preference. You need to understand the variety of grades available to choose the best selection. Please note that the descriptions we have below are general guidelines.

Ideal Cut

This cut is intended to maximize brilliance, and these diamonds’ typically smaller table sizes can create a great deal of dispersion or ‘fire.’ Ideal quality diamonds are ideal for those who love knowing they have one of the finest things money can buy. This category applies only to round diamonds.

Excellent

For round diamonds, many Excellent Cut diamonds have cuts equal to any Ideal Cut diamond, though they are available for slightly lower prices than AGS Ideal Cuts. They provide maximum fire and brilliance. Like the Ideal Cut, these are also for the person who enjoys knowing he has one of the finest things money can buy.

Very Good

The very good-grade diamonds reflect most of the light that enters them, creating great brilliance. These diamond cutters have chosen to stray slightly from the preferred diamond proportions to create a larger diamond. As a result, these diamonds will fall slightly outside most of your customer’s preferences regarding, say, the table size or girdle width. However, in most cases, many of the parameters of diamonds in this range will overlap with specific parameters of diamonds in the excellent and ideal ranges. Generally, the price of these diamonds is slightly below that of the Excellent cuts.

 Good

Diamonds reflect most of the light that enters them. Their proportions fall outside the preferred range because the cutter has created the largest possible diamond from the original rough diamond crystal rather than cutting the extra weight off to create a smaller diamond in the excellent range. Diamonds in the Good range offer excellent cost savings to customers who want to stay on a budget without sacrificing quality or beauty.

Fair & Poor

A diamond graded as poor or fair reflects on a small proportion of the light that enters it. These diamonds are often cut to maximize the carat weight over most other considerations.

The Characteristics of a well-cut diamond are Superior Fire, Brilliance & Scintillation.

•         The Brilliance of the diamond relates to the reflection of white light.
•         Fire, on the other hand, is the dispersion of light into the colors of the rainbow.
•         Finally, Scintillation is the play of contrast between light and dark areas—it’s the sparkle.

Diamond Anatomy

Wondering what on earth is the diamond’s pavilion? Table? Culet? The graphic and supporting text below explains a diamond’s various “parts.”

Diameter

The width of the diamond is measured through the girdle.

Table

This is the large, flat top facet of a diamond.

The Crown

This is the upper portion of a cut gemstone above the girdle.

Depth

This refers to the height of a gemstone (Diamond) from the culet to the table.

Girdle

The narrow rim of a diamond separates the crown from the pavilion. It is the largest diameter of any part of the stone.

Culet

The culet is the tiny facet on the pointed bottom of the pavilion and is the portion of a cut gem below the girdle.

Pavilion

The lower portion of the diamond is below the girdle. It is sometimes referred to as the base.