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Diamond Cut

Diamond Cut

As the single human contribution to a polished diamond's beauty, cut is perhaps the most important, yet most over-looked, of The Four C's of diamond quality. How does cut affect a diamond's value and beauty? A good cut gives a diamond its brilliance, its dispersion, its scintillation-in short, its life. And brilliance is what a diamond is all about, especially in the eyes of the consumer.

The particular angles and finish of any diamond are what determine its ability to handle light, which leads to brilliance. Several factors are considered:

A well-cut diamond reflects light back to the eye evenly in the face-up position, with no dark areas. Dark or 'dead' areas are due to poor cutting, and should not be confused with the faint "bow-ties" which are typical of fancy shapes; in the case of fancy shapes, bow-ties are where the main brilliance and life of the diamond are least apparent.

As you can see from the illustrations below, when a diamond is well-cut (either a fine cut or an Ideal cut), light enters through the crown or top portion of the diamond and travels all the way to the pavilion where it reflects from one side to the other - intensifying in the mirror-like facets as it travels - before reflecting back out of the diamond through the crown and to the observer's eye.

This brightness that seems to come from the very heart of a diamond is known as brilliance. It is the effect that makes diamonds unique among all other gemstones. While other gemstones also display brilliance, none have the power to equal the extent of diamond's light-reflecting power.

In a poorly cut diamond, however, the light that enters through the crown reaches the pavilion facets and then 'leaks' out from the sides or bottom of the diamond rather than reflecting back to the eye.

It refers to the qualities imparted to a diamond by the skill of the diamond cutter. The term "finish" covers every aspect of a diamond's appearance that is not a result of the diamond's inherent nature when it comes out of the ground. The execution of the diamond's design, the precision of its cutting details, and the quality of its polish are all a consideration when a gemologist is grading finish. If you examine a diamond's grading report, you will see its finish graded according to two separate categories: polish and symmetry.

It refers to any blemishes on the surface of the diamond that are not significant enough to affect the clarity grade of the diamond. Examples of blemishes that might be considered as 'polish' characteristics are faint polishing lines and small surface nicks or scratches.

It refers to variations in a diamond's symmetry. The small variations can include misalignment of facets or facets that fail to point correctly to the girdle (this misalignment is completely undetectable to the naked eye).

Major symmetry problems are often seen in diamonds graded as Fair or Poor; they can include severe misalignment of facets, a noticeably off-center table or culet, a noticeably 'wavy' girdle, or a table which is noticeably not parallel to the girdle. However, these types of problems are not a consideration when buying a diamond from Jewelry Depot, Inc. (JD Houston) because we do not sell any diamonds graded as Fair or Poor.

In this technological and mechanized age, diamond cutting is still done by hand, not by machine. Professional cutting requires knowledge of the stone, a precise touch and flawless judgment.

Diamond cuts are broadly graded as Ideal, Excellent, Very Good, Good, Fair or Poor.

Jewelry Depot, Inc. (JD Houston) will classify a diamond as Ideal only if it meets the highest qualifications established by the American Gem Society's Gemological Laboratories. These are strict standards set for proportion, symmetry and polish. Be wary of retailers who call a stone Ideal without a Diamond Quality Report (DQD) from the AGS Labs to back up their claim.

We sell only those diamonds which are graded as Excellent (AGS Ideal) through Good. Excellent and Very Good diamonds are true works of art-perfect examples of the beauty and brilliance that a skilled cutter can impart to an already beautiful gem. Good diamonds are also a credit to the cutter's skill; though there are minor finish or symmetry characteristics in such diamonds, they are undetectable to the naked eye.

Jewelry Depot, Inc. (JD Houston) does not sell Fair or Poor quality diamonds, and we strongly recommend that you avoid these qualities, no matter where you ultimately choose to purchase your diamonds. In the long-run, the cost savings of buying such diamonds does not make up for the loss of brilliance or life in the stone.

Well Cut or Not To determine if a diamond is well cut and proportioned you will need an understanding of how a diamond actually 'works.'

The table is the largest and top-most facet on the diamond's crown. The table percentage is the value which represents how the diameter of the table facet compares to the diameter of the entire diamond. So, a diamond with a 53% table has a table which is 53% as wide as the diamond's outline. For a round diamond, gemologists calculate table percentage by dividing the diameter of the table, which is measured in millimeters (this millimeter measurement does not appear on diamond grading reports) by the average girdle diameter (an average of the first two millimeter measurements on the top left-hand side of a diamond grading report). For a fancy shape diamond, table percentage is calculated by dividing the width of the table, at the widest part of the diamond, by the millimeter width of the entire stone (this total width measurement is the second of the three millimeter values in the top left-hand corner of the diamond grading report.

Contrary to popular misconception, having a small table percentage (53% to 57%) does not make a round diamond any more brilliant than a diamond with a larger table. Rather, the table percentage plays a far more subtle role in the interaction between a particular diamond and the visible light surrounding it. It is meant to reflect and return white light to the eye, creating those quick flashes of light you see as a person tilts the diamond back and forth during normal movement. These quick flashes of light are known as scintillation. Arranged around the table are several smaller facets (bezel and star facets) angled downward at varying degrees. These facets, and the angles at which they are cut, have been skillfully designed to break up white light as it hits the surface, separating it into its component spectral colors-red, blue, green and the like. This effect, which appears as a play of small flashes of color across the surface of the diamond as it is tilted, is what we refer to as the diamond's dispersion (also called "fire"). This play of color should not be confused with a diamond's natural body color (normally white, though sometimes yellow, brown, pink or blue in the case of fancy color diamonds) which is uniform throughout the entire diamond, regardless of whether it is being tilted or not.

If you are still concerned that a diamond with a larger table might somehow look 'less beautiful' than a diamond with a smaller table, please consider the following examples of the difference between two table sizes: in a 1 carat diamond, the difference between a 57% "ideal" table and a table of 59% (which is just outside the traditional ideal range) is a mere 0.13 millimeters - this is just slightly more than the thickness of a single human hair! And while the difference between a diamond with a 57% table and one with a 62% table might sound dramatic, even this represents a difference of less than 0.30 millimeters. These subtleties are very hard to detect with the human eye.

As you may have noticed, brilliance was not mentioned at all in the above explanation. This is because brilliance is not really a consideration when discussing the table. To understand brilliance, we must look at another part of the diamond -the angles of the crown and the pavilion.


Most of the information you hear about diamonds refers to the most common and most traditional cut, the round brilliant. In general, the same facts are true of fancy cuts, though there are a few differences.