Diamonds are cut in many forms. However, the classic cut is the round brilliant. It is the perfect cut which transforms the insignificant rough stone into a fiery, scintillating gem.
Theoretical Basis
Diamonds are cut in many fancy shapes: there are navettes, baguettes, pears, square- or emerald-cuts. Among them, however, the classic is the round brilliant of eightfold symmetry. This style of cut has probably experienced the longest and most intensive history of development; it began as long ago as the first century B.C. and only in this century did it attain its zenith in the form of a circular brilliant cut. This style of cut is already so closely associated with diamond that today the latter is generally called a "brilliant" irrespective of the form in which it is cut Strictly speaking, however, the brilliant is a style of cut which is sometimes used with other gemstones too, for instance, with small rubies, sapphires and zircons.
Uncut diamonds give no hint of the unique optical properties of the cut stones. Rough diamond hides its beauty beneath a yellow, brown or grey tinted "coat", a non-transparent skin which covers many rough stones. Only cutting can transform the unattractive "pebble" into that crystal-clear stone which, in clarity, luster and magical scattering of prismatic colors, surpasses all other precious- stones and has fascinated men for centuries.
The beauty of a cut diamond resides not only in an innately favorable body color, by which the human eye is generally first attracted. It lies, rather, in its superlative optical properties, particularly its high refractive index and color dispersion. The brilliant displays these properties in a fascinating manner, for in the cut state all those factors are in operation which, in optical harmony with one another, create the highest degree of brilliance.
Maximum brilliance - the interwoven concord of luster, light refraction, total reflection, color dispersion and scintillation - is not only the result of the practical experience and masterly craftsmanship of the cutter: what is needed, rather, is the knowledge and application of physico-optical laws in developing an optimal form of cut.
Only when precisely calculated planes and angles are used in the brilliant cut does the stone attain its greatest possible beauty. The following sections, therefore, are concerned with the physical fundamentals, in so, far as they are necessary for. understanding the processes in and on a diamond.
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- Girdle diameter
- Table diameter
- Table ratio measurement
- Table comparison method
- Total height
- Crown height
- Estimation of crown height - Examination of pavilion facets
- Estimation of crown angle - Estimation of the profile
- Girdle thickness
- Pavilion depth
- Sideways reflection to estimate pavilion depth
- Table reflection to estimate pavilion depth
| Brilliance |