Diamond Cut

Cut is probably one of the least understood and one of the most important of the four C’s.

Cut is not to be mixed up with shape. Cut refers to the angles and percentages that diamonds are cut to reflect the maximum amount of light. To understand cut, first you must understand the basic parts of a diamond.

  • Table: Octogonal flat facet on the top of the diamond
  • Crown: Portion of the diamond from the girdle to the table
  • Girdle: The flat section seperating the crown and pavilion
  • Pavilion: Portion of the diamond from the girdle to the culet
  • Culet: The point at the bottom of the diamond
  • Diameter: The measurement of different points of the girdle usually given a minimum and maximum millimeter measurement
  • Depth: The measurement from the table to the girdle
  • Kite Facet: The large kite shaped facet on the crown
  • Upper Girdle Facets: The small secondary facets above the girdle
  • Star Facets: The small triagular facets on the crown surrounding the table
  • Pavilion Mains: The large inverted “V” shaped facets on the pavilion
  • Lower Girdle Facets: The smaller “V” shaped facets on the pavilion
  • Crown Angle: The angle of the kite facet using the girdle as 0°
  • Pavilion Angle: The angle of the pavilion main using the girdle as 0°
  • Depth Percentage: The percentage of depth based on the diameter
  • Table Percentage: The percentage of table based on the diameter

rough diamond planning

When a diamond is cut, the diamond cutter will mark out the shape of the diamond on the rough crystal so that he may measure the shape and determine what the diamond will weigh after it is finished.

The diamond cutter will rarely cut for maximum light return. Usually the diamond cutter will try to cut the heaviest diamond possible from the rough he has been given.

He will measure the diameter and the depth of the marked drawing. If for example the diameter measurement is six millimeters, and the diamond is cut to good proportions the finished diamond should weigh about 0.80 carats. If the diameter measures six and a half millimeters, and the diamond is cut to good proportions the finished diamond should weigh one carat.

Chances are the diamond cutter will be cutting for weight retention. The cutter knows he can sell a one carat diamond for considerably more than a three quarter carat. Using the example from above, if the marked drawing measures six millimeters in diameter he only needs to cut the pavilion deeper and the crown higher therby maximizing the weight retention and making the finished diamond weigh one carat.

The effect on light return however is substantial. The total depth of the diamond has been increased as well as the pavilion and crown angle being increased which will cause the diamond to leak light as opposed to reflecting it back to your eye (see below).

light performance ray

Ray path inside of a well proportioned diamond vs one that is poorly cut.