The Ideal Cut diamond is one in which the light entering from the top and sides of the diamond is reflected back through the top to the viewer. This gives the most brilliance and sparkle and is how a diamond is really supposed to be.
This is achieved by the cut. The light rays from all sides should bend towards the center and reflect back through the top in a blaze of light.
If the diamond is poorly cut, say too narrow or too deep, then not all the light rays will do so and some will be lost resulting in a less brilliant stone. In a diamond that is cut too deep in fact it may even appear black in the center of the stone due to lost light. In a shallow cut stone the light ‘leaks’ through the bottom and the diamond will give off a dull reflection.
The ideal Cut is achieved through a special mathematical formula designed for cutting diamonds to a specific set of proportions discovered by Marcel Tolkowsky in 1919.
It is important to know this when buying a diamond as, for example, although a deeper stone may have more carat weight but would not be such a desirable stone as the ideal cut with a lesser carat weight. Care should be taken when buying discounted diamonds because of this. A jeweler promoting the higher carat weight may omit to inform you of the deeper cut and the resultant less reflection and brilliance of the stone and corresponding less value. In short it may not be such a bargain after all.
For the technically minded the actual proportions needed to produce the maximum brilliancy consistent with a high fire quality in a round diamond are computed as a percentage of the girdle diameter, are as follows: total depth, 59.3% (without provision for girdle thickness); crown depth, 16.2%; pavilion depth, 43.1%. The bezel angle is 34° 30% and the pavilion angle is 40° 45%.
Ask the jeweler or dealer if the cut is a Ideal Cut and get him or her to put it in writing.
There is no substitute for getting a independent appraisal also and doing your own due diligence.
That way you can be sure you are getting the ideal diamond in the form of an Ideal Cut!