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Cut is the result of a craftsman's skill in transforming a rough diamond into a breathtaking gem. A diamond has facets that allow light to enter it, become refracted, and exit in a rainbow of colors. So it follows that a better cut diamond does a better job of dazzling us with its beauty. Here's the 'secret' to how a diamond sparkles:
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The Way Diamond Handle Light
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As you can see, the diamond with the correct proportions does a more effective job of refracting light out the top of the stone to your eye. The less-than-ideal cut diamonds allow some light to become lost out the bottom.
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Diamond Properties
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There are many measurements that go into creating a diamond that truly maximize the refraction of light. Facets must be cut at exactly the right angles relative to one another; the top and bottom halves of the stone must have the proper depth relative to each other; the table, or flat surface on the top, must be the correct size, relative to the overall size of the stone. And, of course, the facets on the top (crown) and bottom (pavilion) must align correctly with each other. Here is a diagram showing a diamond's basic proportions:
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These measurements and percentages are different for each diamond, and are all taken into account in the evaluation of a diamond's cut. In fact, each diamond shape (heart, round, oval, emerald, etc.) has its own set of guidelines for what makes a Premium or Good cut.
An 'ideal cut' is a specific set of guidelines that delineate the proportions that give a diamond the highest amount of fire and brilliance.
Although the proportions of an ideal cut vary depending on the source you talk to (from jeweler to jeweler, country to country), there are certain ranges that are generally accepted as capable of evoking the most desirable fire and brilliance from a stone. These ranges must cause the light entering the diamond to be reflected and dispersed through the table (top), not through the sides or bottom.
But most of all, an ideal cut diamond must be cut to bring out the stone's brilliance and fire, not retain the most weight from the rough cut stone.
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Round Brilliant Diamond Cut Grades
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| GRADE |
TABLE PERCENTAGE |
DEPTH PERCENTAGE |
| Ideal |
53% - 57% |
59% - 62% |
| Premium |
58% - 63% |
58% or 63% |
| Good |
64% - 65% |
57.5 or 64% |
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It's important to note that some independent grading laboratories do not grade a diamond's cut, while others do. The Gemological Institute of America (GIA), for example, will only give an evaluation of the quality of a diamond's cut for round brilliant diamonds. For all other diamonds, only the shape and measurements of the stone are part of the report. It does, however, give the proportions of the diamond (depth and table percentages), girdle thickness, and culet size (if any) as well as a general rating of the stone's finish, including its polish and symmetry.
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Symmetry
Symmetry describes several factors: how the facet edges align with each other; whether the corresponding facets from opposite sides of the diamond align with each other or not; and whether the facets from the crown, or top of the diamond are properly aligned with the corresponding ones on the bottom (pavilion). When choosing a diamond, look for Excellent, Very Good or Good ratings on the grading report, if symmetry is graded.
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Fluorescence
When exposed to ultraviolet light, small percentages of diamonds fluoresce, or emit light, which may be yellow or blue. Fluorescence does not necessarily affect a diamond's value, however it is listed on a diamond grading report.
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The bottom line
When it comes to judging cut, the most important thing to remember is that quality and craftsmanship are more important than size, since these characteristics can mean the difference between a positively radiant, lively diamond, and a lifeless, lackluster stone (that may, in fact, be larger). Remember, diamonds have more value if they have been cut to maximize their brilliance, not their size. All in all, cut must be balanced along with the rest of the 4Cs in order to find the highest quality diamond your budget will allow.
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