When it comes to the 4C grading system for diamonds (for both natural diamonds and lab grown diamonds), there's no question that cut has the biggest impact on a diamond's sparkle and fire. But why is it that fancy-cut diamonds, such as heart-shaped, oval, and pear-shaped diamonds, don't have a cut grade like their round-cut counterparts? The answer lies in the fact that the International Gemological Institute (IGI) and Gemological Institute of America (GIA) only provide cut grades for round brilliant-cut diamonds, while the American Gem Society (AGS) provides cut grading for round and princess-cut diamonds. Both of these well-known grading systems were established relatively recently, in the 2000s.
So why can't fancy-cut diamonds be graded in the same way as round-cut diamonds? If it's possible to grade round brilliant-cut diamonds, why not establish a comprehensive grading system for oval or pear-shaped diamonds? One might assume that it wouldn't be too difficult to create such a system. But the reality is, it's not that simple.
The fancy cutting of diamonds is based on two main cutting styles: brilliant cut and step cut. By lengthening, shortening, adding or removing facets from the crown and pavilion of the gemstone, there are almost infinite ways to adjust the shape of the diamond to maximize its sparkle, fire and brilliance.
Some cutting styles are used to create a "crushed ice" effect, which makes the diamond shimmer from every angle; by adding shorter facets to the pavilion, the light is reflected and refracted back to the viewer's direction at a higher speed. Other styles that feature elongated facets can emphasize the subtle glow of traditional old-cut diamonds, and their intense fire is particularly prominent in light.
Each of these styles has its own beauty, but which one has better cut quality? Some people prefer longer facet styles with strong fire and brilliance, while others prefer crushed ice styles. Although "beauty" is highly subjective and differs for each individual, everyone agrees that each shape should meet certain criteria to be called "ideal."
Fire, brilliance, and scintillation - these qualities all depend on adjusting the actual length and angle of the gemstone's facets through mathematical formulas to create a perfectly symmetrical structure that allows light to reflect accurately within the gemstone. This is the crux of the issue: how to evaluate the actual dimensions, depth, and crown angles of each diamond to ensure its cut is perfect.
A simple and easy-to-understand chart is used to illustrate the relationship between the grading of each fancy cut diamond's cut quality from "excellent" to "good" and the diamond's depth and table percentages. The total length of the diamond's facets or the diamond's total depth divided by its diameter gives us the percentages of the table and depth of the diamond, respectively. For example, if a diamond has a total depth of 5.6mm and a diameter of 10mm, its depth percentage would be 56%. This formula can help us determine the diamond's brilliance as it is adapted from the ideal cut proportions formula for round diamonds, which can be graded. By examining the facet style of the diamond's crown and referring to its clarity chart, we can roughly assess the diamond's cut quality.
ROUND | DEPTH 60.1-61.9% | TABLE 55-58.5% |
PRINCESS | DEPTH 64-73% | TABLE 65-74% |
EMERALD | DEPTH 60-68% | TABLE 57-69% |
ASSCHER | DEPTH 59-68% | TABLE 57-69% |
So why don't these fancy cut styles have official ratings from GIA and IGI? It's simply because there are too many variations that can occur with each shape, making it difficult to evaluate each one individually. Each year, new styles are derived from existing shapes, resulting in increasingly diverse brilliance and beauty. However, this situation is changing as the jewelry industry gradually agrees that specifications such as diamond depth percentage, facet percentage, length-to-width ratio, etc., should be followed, and cut grading for different gemstones will become standard practice.
However, for now, the beauty of fancy-cut diamonds can only be evaluated subjectively. The overall appearance of a diamond must be stunning, with dazzling brilliance and fire. If possible, it's recommended to choose a diamond with excellent polishing quality and symmetry, as this indicates that the facets are arranged neatly and polished smoothly, allowing light to pass through the different parts of the stone clearly. You can seek advice from a jeweler or a gemologist to learn which combination of facet and depth percentages can create the most beautiful cut ratio and which length-to-width ratio can make the diamond's shape appear most natural.