The Cut of a Diamond
Diamond cut generally refers to two different aspects of diamonds: 1) The diamond's shape or style; and 2) the diamond's proportions and finish or make.
Shape (Style)
Because of a diamond's extreme hardness, for years the way a diamond could be shaped was by rubbing two diamonds together or by rubbing the diamond against a file charged with diamond powder. There are very few things which can cut a diamond besides another diamond. Although laser-cutting techniques are also now employed, many diamonds today are still cut and polished with saws and polishing wheels that are charged with diamond powder. Lasers allow cutters to extend the range of possible shapes which were unattainable before. The round brilliant cut diamond is still one of the most popular of all styles, but many fancy shapes are popular as well. Often the shape of the rough diamond determines which "style" the diamond will be cut. Most styles have one of three basic facet arrangements: brilliant, step, or mix. Many diamond experts believe that brilliant cuts display maximum brilliance, while step cuts display maximum color, and mixed cuts demonstrate a combination of the two.
Brilliant cuts include Rounds, Marquise, Oval, Pear, Heart, Princess and Trillion TM while Stepped cuts include Emerald, Baguettes, and Triangle. The less common mixed cuts would include, the Barion Cut, Flower Cuts, and Royal Cuts.
 |
 |
 |
 |
| Round | Marquise | Oval | Pear |
 |
 |
 |
 |
| Heart | Princess | Trillion | Emerald |
Proportions and Finish (Make)
As noted in previous sections (carat, color and clarity) every aspect of a diamond is measured in subtle and minute differences. Weights are measures in tolerances less than 1/10,000 of an ounce, color in subtle nuances, and clarity under ten-power magnification. This same precision is found in a finished diamond of proper make. A diamond's proportion and finish are the only human-controled factors of the 4 Cs, yet they directly affect the weight, color and clarity of a finished stone, and are the single biggest factor in a diamond's brilliance, fire, and scintillation- the factors which make diamonds uniquely beautiful. Although each diamond style has proportions which yield that shapes maximum brilliance, we'll focus on the round brilliant diamond because of its popularity and symmetry (which produces an even display of brilliance, fire, and scintillation).
A round brilliant diamond generally has 58 facets (flat cuts)-- 33 on the crown (upper portion of the diamond) and 25 on the pavilion (lower portion). In addition a diamond's refractive index (in this case determined by its chemical composition), the placement, size, symmetry, and angle of these facets help determine the overall diamond's brilliance, fire and scintillation. Let's define these three beauty factors.
Brilliance is the total amount of light reflecting to the eye from within the diamond and from its surface.
Fire or Dispersion is the rainbow of colors, which are seen when white light separates in a prism effect.
Scintillation is the white flashes of light reflected from a stone's facet when you, or the light moves.
These three beauty factors are determined by a diamond's proportions as follows:
Table Size
The table is the window to the heart of the diamond, but size plays an important factor in dispersion. Many cutters like to cut large tables to retain more of the original rough weight, but a table which is too large, not only unbalances scintillation (its reflection creates a flash that overpowers the reflection from other facets) but also reduces dispersion. Most experts agree that a table that is approximately 54% the width of the diamond is the ideal size. In a table this size the table outline tend to bow into the center of the stone. When the table lines are straight, the table size is approximately 60% (if the star facets are of normal length). Table lines, which bow out, generally indicate a table size larger than 60%.
Crown Angle
The combination of table size and crown angle affect the brilliance of the diamond. The crown angle is the angle (from a side view) of which the crown raises above the girdle plane. The ideal crown angle is 34 1Ú2 degrees. (Thirty-four and one half talk about precision!) A crown angle which is too shallow, displays a loss of fire, and when combined with a large table, the diamond loses brilliance. A crown angle which is too steep, causes the light to exit the stone in a direction which is not viewable face up. Estimating crown angle is the most difficult proportion ratio to determine.
Girdle
An ideal girdle would be thin enough not to collect grease and grime (which thick girdles often do), but not so thin that it risks chipping (which is what very thin girdles do). Thick girdles also often are seen as fuzzy reflections in the table.
Pavilion Depth
The ideal pavilion depth is about 41 degrees or about 43% of the girdle diameter. A shallow girdle, of less than 40% often causes a girdle reflection known as a "fish-eye," whereas a deep girdle of 45% often causes a dark center known as a "nail-head." One of the best ways to estimate pavilion depth is to look for the reflection of the table in the bottom of the stone. (as seen face up)Ê If the reflection is about one-third of the way from center to the actual table corner, then the pavilion is about 43% depth.
When light enters a stone the depth and angle of the pavilion and crown must be very precise in order for the light to return to the eye. A diamond which is cut too shallow, causes the light to reflect at an incorrect angle and much of it is lost before it returns to the eye. A diamond which is cut too deep, cannot strike the first angle properly and it much of the light passes through the stone before it can reflect back to the eye.
Finish
A diamond's finish is divided into two categories: 1) Symmetry; 2) Polish. These factors are rated in five degrees-- excellent, very good, good, fair and poor. A well-made diamond has even symmetry and properly aligned and pointing facets. Less than ideal symmetry may leave diamonds with misaligned or misshapen facets, facets that do not come to points, off-center tables or culets, out-of-round girdles, tables not parallel to the girdle plane, or wavy girdles. A well-polished diamond will appear shiny and will not leave visible polish marks or blemishes. A less than ideal polish may leave a diamond with a fuzzy or dull look, polishing marks, and minor blemishes including scratches, nicks, pits, and rough girdles.
Classes
Diamonds are often grouped into Classes 1 through 4 (1 being the best). Below is a chart showing the differences in diamond classes. As you review this chart you might keep in mind that the Jewelry industry generally center on the Class 2 diamonds (in fact Class 2 stones are often the highest quality that many stores stock. Class 1 diamonds can cost 15% more than Class 2 stones, while Class 3 diamonds can cost 15% less than Class 2 stones. A Class 4 diamond can cost 50% less than a Class 2 diamond.
| Class I | Class II | Class III | Class IV | |
|---|---|---|---|---|
| Table Size | 53-60% (61-62% for under .50 ct.) |
61-64% | 65-70% Stone often "stretched" in attempt to achieve higher weight categories |
Over 70% Untrained eye can see something amiss even if unsure what is wrong |
| Crown Angle | 34-35 degrees | 34-35 degrees | 30-32 degrees | Less than 30 degrees |
| Girdle Thickness | Medium to slightly thick | Thin or thick | Very thin or very thick | Extra thin or extra thick |
| Pavilion Depth | 43% | 42-44% | 41-46% | Less than 41% or more than 46% |
| Culet | None to medium | Slightly large | Large | Very large |
| Finish | Very good to excellent | Good | Fair | Poor |
The question might be asked: Why aren't all diamonds cut to ideal proportions? The answer is cost per carat rough, verses cost per carat yield. For example: Suppose a diamond cutter buys a rough 1.00 ct. stone for $1000 per carat and he wants to make $100 profit. If he cuts the diamond to less than ideal proportions he may end up with a stone weighing .60 ct. He would sell that stone for $1100 (his cost plus his $100 profit). The .60 ct. diamond would thereby sell for $1833 per carat (.60 [ct.] x $1833 [per ct.] = $1100). On an ideal cut stone, however, the rough diamond may yield a stone of only .40 ct. The cutter still has his $1000 cost into the stone and he still wants to make his $100 profit, but a finished diamond of .40 ct. would thereby sell for $2750 per carat (.40 [ct.] x $2750 [per ct.] = $1100). To use an analogy, if you went to a restaurant and purchased two steaks weighing 16 oz. each after cooking- one with the fat already trimmed away and one with the fat intact- you'd pay more for the steak with the fat trimmed away. The reason an ideal cut diamond usually weighs less than one-half of its rough weight is because the diamond-- in effect-- is taken from the heart of the stone. You'll notice in the photos below that with the non-ideal cut there is plenty of room left above the diamond to cut another small stone. With the ideal cut, however, there is barely enough room for a very small diamond to be cut from the remaining stone. Quality control, expertise, and time are other factors of why not all diamonds are cut to ideal proportions. Where it may only take fifteen to twenty minutes to cut a commercial grade diamond, it may take from four to thirty or more hours to cut an ideal-cut stone.
The American Gemological Society (AGS) has developed a CUT grading scale of eleven different grades similar to GIA's clarity grading scale. Grade "0" is the best, or and "Ideal Cut." Grade "1" is "Excellent," grade "2" is "Very Good," grade "3" is "Good" and so on down the scale. Grade "10" is the lowest and poorest of all round brilliant cuts. Just as all other diamond scales are based on very minute differences, so likewise, the AGS Cut scale is based on very subtle differences. An "Ideal Cut" diamond would have measurements, which meet the exacting standards described above. A "Super Ideal Cut" diamond has zero deductions in all seven categories and is considered the highest achievable cut rating.
Trained experts can accurately grade the cut of a diamond. Just by sight, an expert can tell a diamonds table percentage, crown angle and pavilion depth to a surprisingly accurate degree. And although many experts can show a customer some generalities when looking for a well-cut stone, it's often difficult for the consumer to be able to tell accurately the different cut factors. You can buy a diamond from us with the confidence of knowing that trained experts from the strictest laboratories have graded your stone with the latest diamond grading tools to assure the most accurate grades. Few other competitors can boast that.
