As the single human contribution to a polished diamond's beauty, cut is perhaps the most important, yet most over-looked, of the Four Cs 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:
Proportion:
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 most 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 table 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 table 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 table reaches the pavilion facets and then 'leaks' out from the sides or bottom of the diamond rather than reflecting back to the eye.
The illustrations above show how light behaves in different cuts of diamond. Note how the light 'leaks' out of the bottom and sides of diamonds that are too deep or too shallow. Well-made diamonds such as Ideal cuts and other fine cuts of diamond return light back to the eye, through the table, for maximum brilliance.
Finish: Finish 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.
Polish:
Polish refers to any blemishes on the surface of the diamond which 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.
Symmetry:
Symmetry 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, a noticeably 'wavy' girdle, or a table which is noticeably not parallel to the girdle.
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.
The better diamond retailers 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.
Diamonds rated Excellent and Very Good by AGS 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.
First, you 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.
Diamonds have many wonderful natural properties - their unique and incomparable hardness for one - but they are not particularly brilliant or glittery when they first come out of the earth. What, then, brings out the brightness from within the heart of these stones? The key to it all lies in the angles of the crown and pavilion.
The crown:
For a round diamond, in order for the crown to provide sufficient fire, the bezel facets should be cut within a specific range of angles (usually between 33 and 35 degrees). However, this range is merely a guideline, not a hard-and-fast rule that must be adhered to in every case. At the outer points of this range, you might find diamonds with crown angles of as little as 31.5 degrees and as much as 35.9 degrees which are still very attractive. These angles do not affect the diamond's table percentage in any way. It is possible for a diamond's crown to have any combination of crown angles and table size that a cutter desires.
The pavilion: The most overlooked part of the diamond:
The pavilion is the part of the diamond that lays just below the girdle. It is easy to see why people often neglect to consider it's contribution to a diamond's beauty; when a diamond is set, typically only the crown stands out prominently, and the girdle and pavilion are hidden beneath prongs or bezels. They seem to serve only the utilitarian purpose of providing a way to hold the diamond in place. However, it is this hidden part of the diamond that is the key to brilliance.
So, how does brilliance work exactly?
The secret is in the pavilion angles, which, in a round diamond, should typically be between 40.5 and 41.5. Unlike crown angles, variations in pavilion angle can produce drastic and, in some cases, devastating differences in the appearance of a diamond. However, even here, the rules allow some leeway for a cutter who is trying to perfect his art. For example, according to AGS, a round diamond may have a 40.25 degree pavilion and still be considered an "ideal cut." The best diamond retailers generally avoid carrying diamonds with even this subtle degree of variation, as it sometimes creates a mild "fish eye." A fish eye is the reflection of a diamond's girdle that is visible through the table; it appears as a faint white ring in the center of the diamond (the effect looks like a fish's eye, hence its name). Even though we generally prefer to avoid these diamonds, we want to emphasize that having a 40.25 degree pavilion angle does not necessarily mean a diamond will display a fish eye or that it will be 'ugly' in any way. Diamond cutting is an art, not a science, and cutters learn, through years of experience, to consider all aspects of their finished product. While a certain pavilion angle may not achieve the proper look in combination with one set of crown angles and table sizes, when the same pavilion angle is paired with a different arrangement of crown facets, the result can be stunning.
That said, there are still some variations on pavilion angle that are very definitely unacceptable. Cutting a pavilion of 40 degrees (just ? degree shallower than the standard!) produces what is considered industry-wide to be a very clear-and very undesirable-fish eye. And on the deeper side of the spectrum, while a 42 degree angle can still produce a beautiful diamond, anything deeper than that will create a "nail head"-a dark, lifeless spot in the center of the stone caused when the light entering the diamond is lost in the bottom of the pavilion and fails to reflect back through the crown to your eye.
Ovals, pears, hearts, marquises, emerald cuts, princess cuts, radiants and trilliants
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 which you ought to keep in mind:
Table percentages and crown angles on a fancy shape:
As with round diamonds, the table percentage and crown angles of a fancy shape diamond do not affect its brilliance. While some people may have personal aesthetic preferences for smaller or larger tables on round diamonds, these same percentages do not apply to the fancy shapes. For example, while an 75% table would be unthinkable on a round diamond, it is quite common and quite attractive on a princess cut. In this sense, the standard or 'ideal' proportions for a round diamond do not apply to the fancy shapes. Because of their unique designs, there are many more variations possible for the fancy shapes than for rounds (i.e. how many pavilion facets they have; the length-to-width ratio; the prominence of their respective lobes and wings; whether their points are cut as French tips or standard tips). Therefore, there is no equivalent of an 'ideal cut' among the fancy shapes. Though there are most certainly acceptable and unacceptable ranges for each shape, attractive proportions are based more often on judgment calls and personal taste.
The myth of the 'bow-tie free' fancy shape:
Theoretically, in a round diamond, all angles and facets are perfectly symmetrical. This creates an even brilliance and play-of-light throughout the diamond. With fancy shapes, however, pavilion angles differ not only from diamond to diamond but also from one part of a diamond to another part of the same diamond. This is because, in order to meet at the same point, angles running from the [longer] length of the diamond to its center must be shallower than the angles running from its [narrower] width to the center. As a result, the light reflected back to the eye from the pavilion differs from point to point within any given diamond. This effect is manifested in the form of small patterns, known as bow ties, in the diamond's center. They are so-called because they often look like two little triangles attached to one another in the shape of a man's bow tie.
These bow ties are not an option, but rather, an integral part of every fancy shape. While some people incorrectly regard bow-ties as a negative aspect of fancy shape diamonds, the truth is that they are the main source of brilliance and life in these diamonds. A good cutter does not try to minimize their appearance; rather, he craftily uses angle variations to expand these bright bow-ties and to bring out similar levels of brilliance throughout the rest of the diamond.
As with round diamonds, careful design of a fancy shape relies heavily on the pavilion. Most fancy shapes require deeper pavilions than round diamonds do in order to achieve the same amount of brilliance.
With round diamonds, a total depth percentage in the upper 50s or lower 60s results in a beautiful diamond. However with princess and radiant cuts, this depth would create a diamond that looked like glass - not at all like the diamond you would expect. This is because more of the weight, and more of the depth, in a fancy shape must be dedicated to the pavilion in order to create the proper angles for light to be reflected back to the eye. Therefore, in a princess or radiant cut with a proper crown, a total depth of 70% or more is not uncommon for well-made diamonds. These two shapes generally require the greatest depths of all the fancy shapes.
Emerald cuts differ a bit from most of the other fancy shapes. Rather than having facets that radiate out from the diamond's center to its edge, emerald cuts have facets that are arranged in concentric rows around the diamond. These types of facets reflect light in a different way than the other shapes do. They also require a slighter greater depth percentage than rounds.
Despite the fact that some shapes require greater depth than others, you should not obsess too much over total depth percentage. Remember that, in the end, brilliance is based less on the total depth of a diamond than on how that depth is distributed, and on how the depth interacts with the particular crown and pavilion angles of the diamond.
Finally, keep in mind that most of the 'facts' that you hear about diamonds are really just the opinions and preference of one party or another. Different jewelers have different theories on what makes a diamond beautiful; they market these ideas to customers in order to create the sense of a unique brand of diamond that their customers can feel comfortable with. These theories are not necessarily 'wrong,' but they are also not the only theories that are 'right'. Whenever you see a chart that says the a diamond should be between x% and y% to be beautiful, keep in mind that these boundaries are merely intended as rough guidelines for consumers; you do not automatically risk choosing between a 'good' diamond or a 'bad' diamond in you choose something that lays outside these parameters. These ranges represent only an approximation of the average beautiful diamond. Ultimately, it is up to you to do your homework…..look at a few diamonds and get to know your own personal tastes before you decide to buy.
