Diamonds, like people, are individual and unique yet they have certain basic structural features in common with one another. Every aspect of a diamond has a special name and one’s understanding of how each individual part of a stone contributes as whole will aid you in selecting the perfect diamond to meet your needs. Such features as the brilliance, dispersion, scintillation and proportions of the diamond combine to make it a basic and unique structure.
There are eight standard features common to all diamonds.
The proportions of a diamond refer to the complex, wide-ranging interaction among the shape, angle and size of each facet as it relates to the others of the same stone. For starters, a fifth of all light that falls on the stone is reflected off its surface.
Of the remaining four-fifths of light, some will escape through the bottom of the diamond, and this goes unnoticed by the viewer. A superbly proportioned diamond with all facets well placed and angled will maximize the amount of light reflected back through the crown or top of the stone, to the viewer’s eye. It is this light which is referred to as fire, brilliance and scintillation.
In the illustrations below, three distinct patterns of light can be observed. The light passing through a diamond will either refract or bend, as it passes through the stone, or it will reflect as it bounces off the stone rather than passing through it. The actual cut of a diamond is of great importance since the angle that the light hits the facets will determine if the majority of light refracts or bends.
Should the cut of a diamond be too shallow, light upon entering will hit the facet of the pavilion at too low an angle and refract or pass through the stone’s facet and then exit from the bottom rather than the top of the diamond.
Should the cut of the diamond be too deep, light will enter and hit the first pavilion facet, and then reflect to the second pavilion. In this case, the light striking second pavilion facet at too low an angle will cause it to refract, thus enabling the light to pass through the bottom rather than the top of the stone.
When a diamond is ideally cut, each pavilion facet will reflect most of the light back through the top or the crown of the diamond. And upon leaving the stone, it refracts the bent light to the eye of the beholder and, in the process, a dazzling fire effect is created.
The depth of a diamond is conveyed in mm’s as the distance between the culet located at the very bottom of the stone and the table, located at the very top, when the diamond is viewed from the side.
The measure of a diamond’s depth on a percentage basis is figured by dividing its depth by its width. For example, if the stone is 3.95mm in depth and 6.5mm in width, the percentage of the diamond’s depth is expressed as 60 percent. And the lower the depth as a percentage, the larger a certain carat weight will appear, but with most of a diamond’s depth being in its width rather than its depth.
To calculate a diamond’s table percentage, simply divide the diamond’s table facet width by the width of the diamond. For example, if the table facet measures 6mm in width and the diamond itself measures 9mm in width, its table expressed as a percentage will be 66.7.
The table % of a diamond is calculated by dividing the width of the table facet by the width of the diamond. So, if the table facet is 3.65 mm wide, and the diamond is 6.41 mm wide, its table % is 57.
Please Note: When purchasing a diamond, you should not base your decision solely on the depth or table%. However because the overall cut grade will already include both of these elements, it is recommended you use them as principle factors when selecting a diamond.
It follows that when comparing two diamonds with identical cut grades, the table and depth percentages can then be added to the mix as a further refinement.
All of Damasci’s diamonds are accompanied by a GIA, AGS or IGI grading report which include a diagram representing the outline of the actual diamond. The diagram displays all the proportions of the diamond such as the table and depth percentage, culet and girdle sizes, as well as additional measurements including the pavilion and crown angles.
Symmetry indicates the precision of the shape and how the facets of a diamond are harmoniously arranged. It is a general rule that with diamonds of great clarity, symmetry is essential, whereas diamonds of lesser clarity grades, over all symmetry is somewhat less important.
In the finest diamonds, the girdle is perceived as perfectly flat and parallel to the table.
The girdle will create a less than desirable wavy shape if the diamond cutter fails to properly angle the facets that meet the girdle.
In a perfectly cut round-cut diamond, the top point of the pavilion and the bottom point of the bezel facets align perfectly at the girdle. Any miscalculation resulting in misalignment is considered undesirable.
The positioning of the table, a diamond’s biggest facet, where white light enters and exists the stone, is best when centered at the top of a diamond while remaining parallel to the girdle. Uneven positioning will result when the table is off-center or unparalleled in relationship with the girdle. A table positioned in an off-centered way will results in an erroneous, off-centered look.
To determine if the culet is off-center, imagine 2 lines intersecting at the point of the culet viewed face-up. If the resulting four triangles are asymmetrical, then the culet is off-center. If the four triangles are perfectly symmetrical, then the culet is centered.
These can be found at any point on the diamond but typically appear on the pavilion, or close to the girdle. Extra facets usually occur when a diamond cutter attempts to remove or disguise an imperfection or natural by removing an external inclusion. Although the inclusion is disguised or removed, the diamond’s symmetry and light performance are compromised.
If the crown angle of a diamond is not perfectly parallel with its girdle, the table is perceived as off-center and undermining the symmetry of the diamond. Symmetry is very important for the light performance or brilliance of a diamond.
When a portion of the original rough surface of a diamond has not been polished, this is referred to as a natural. On occasion, naturals are left on the girdle and result in a heavier diamond. Naturals tend to dip towards the crown or towards the pavilion in most cases.
Please Note: Naturals, in essence, do not add size or beauty to the visible eye but rather add to the price.
A perfectly cut Round brilliant diamond best displays all 58 facets to perfection. Sometimes, however, the facets are improperly pointed and because of this fail to meet at a specific point.
A perfectly proportioned table will show an octagon shape of equal sides that are parallel to one another. This diagram displays a table that lacks symmetry due to the improper cutting of the facets.
Polish refers to the smoothness of individual facets of a diamond as measured by a trained gemologist. The finer the polish, the easier it is for light to pass through the stone. Microscopic imperfections created by the polishing wheel will reduce the diamond’s overall brilliance. In order to obtain the greatest possible shimmer, with maximum light passing through the diamond’s facets, an excellent polish is required.
Laboratory certification is helpful when purchasing a diamond. Make sure to select one with good, very good or excellent polish. Any grade below good, such as poor, is not recommended as microscopic imperfections created by the polishing wheel will reduce the amount of reflected light. One might wonder why a good diamond would possess a poor polish, and the answer is simply cost cutting. Excellent polishing requires more time and the greater the time involved, the greater the diamond cutter’s cost.
Diamond polish and diamond symmetry are graded in a similar fashion.
GIA laboratories highest polish grade is Excellent, followed by Very Good, Good, Fair and Poor. AGS and IGI highest polish grade is Ideal, and followed by Excellent, Very Good, Good, Fair and Poor.
Under magnifications, the difference the various polish grades becomes more obvious. The lower grades, including Fair and Poor, suggest that the irregularities in the polish are visible to the unaided eye, thus reducing the perfection and beauty of the stone.
Fluorescence is a naturally occurring phenomenon that a diamond displays when it is exposed to UV rays or black light. While wearing white, the same phenomenon or glow can be perceived under ultraviolet light. Similarly a diamond fluoresces when viewed under UV rays and approximately a third of all diamonds fluoresce to some degree.
There are four distinct categories of fluorescence: faint, medium, strong and very strong, with subtle variations between the various categories. When a stone has a faint grading, its glow is barely visible under UV light. On the opposite end, a very strong grade means the stone has the deepest possible glow which is seen as crystal clear when viewed under UV light. The categories vary and the colors do as well, with green, yellow and white seen while blue most common of the four.
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