Cut - How it Affects Brilliance


Cut is different than shape. Cut refers to how a diamond is proportioned. Shape refers to the outline of the diameter. Some popular shapes are round, oval, square, pear, rectangular, trillion, and heart shaped. Each of these shapes can be cut in different styles of faceting. For instance, when a square shape is cut with triangular and kite shaped facets the cutting style is known as princess cut. When the same shape is cut with long rectangular facets, the style of cut is known as a step cut or an emerald cut. Round diamonds are usually cut in a style with 57 facets known as a brilliant cut.


Proportions determine brilliance. A properly cut diamond will reflect nearly 100% of the light entering the surface. If cut out of proportion, some of this light is lost through the bottom or side of the stone. If a diamond is cut too deep, light goes through the top and out of the side, making the stone look dark. If it is cut too shallow, light goes straight through the top and out of the bottom making it look lifeless.

Diamonds can dance with light. When light enters the flat surface of the table and exits through the angled facets of the crown, a flash of prismatic colors can occur. This is called “dispersion”. When light bounces off the perfectly polished surfaces of diamond facets, a rapid fire spark of white reflected light can occur. This is called “scintillation”. A diamond must be fashioned to catch every beam of light and choreograph its movement perfectly within the stone. If the dance is successful, the light is released back to surface where it is caught by the eyes of those who admire it. This total display of light is known as brilliance.

diamond_cut_clip_facet.jpgA round diamond is not always round. In fact, diameter is usually listed as two measurements, the most narrow to the widest. The flat surface facet called the table may look like it is in the center, but look again. It may not be. Facet corners should meet but they don’t always. The point of the diamond, or culet, should be in the center but sometimes it’s not. When facets are not shaped or positioned exactly how or where they are expected to be, light must find a different path. These variations in symmetry affect brilliance.

One thing affects the other. It’s the combined sum of all the angles, depth, symmetry and polish that will determine how much sparkle your diamond will exhibit. For instance, a larger table will make the diamond look brighter but reduce the dispersion of colors from the smaller crown facets. The effects of a deep pavilion may be camouflaged by a larger table. These are decisions that are carefully considered by the highly trained cutter. In order to achieve the best proportions, he may have to remove up to 50% of the rough diamond.

Differences in Cut are easy to see but not so to define . A diamond that is well cut will seem to inhale light and breathe fire. A diamond that is deficient in cut will be obvious next to such a dazzler. Since there are so many variables in determining the ideal cut, grading in this category has been subject to years of debate. Listed below is a range that most experts would agree upon as the measurements of a beautifully cut diamond. Get the numbers but trust your eyes. Consider the cut with as much emphasis as you would the carat weight, clarity, and color.

Round Diamonds:

  • diamond_cut_clip_size.gifTable diameter: 53-59% of total stone diameter
  • Crown depth: 14-16.5% of total stone depth
  • Pavilion depth: 42-44% of total stone depth
  • Total depth: 58.7-62.3% of diameter
  • Crown angle: 33-36 degrees
  • Pavilion angle: 40-41.5 degrees
  • Girdle 1.5-4.5% (very thin to thick)

Pear, Heart, Oval, Marquise Diamonds:

  • Table percentage of diameter:
    53-62% excellent 62.1-64.0% very good
  • Total depth percentage of diameter:
    59.0-63.0% excellent, 63.1-65.4% very good

Preferred shape (but personal preference rules):

  • Pear: length=1.50-1.75 to width of 1.00
  • Marquise length=1.75-2.25 to width of 1.00
  • Heart length=0.98-1.02 to width of 1.00
  • Oval length=1.33-1.66 to width of 1.00

Emerald and Radiant Cuts:

  • Table percentage of diameter: 59.0-65.0% excellent 65.1-69.0% very good
  • Total depth percentage of diameter: 60-65% excellent, 65.1-69.0% very good
  • Preferred Shape (personal preference is the rule): Length=1.5-1.75 to width of 1.00

Princess Cuts:

  • Table percentage of diameter: 59.0-72.0% excellent 72.1-77.0% very good
  • Total depth percentage of diameter: 64-75% excellent, 75.1-80.0% very good

Mills Jewelers Diamonds are selected for superior cut. Every diamond is individually chosen by our own Graduate Gemologist (GIA) to meet the highest standards for brilliance.

We require certificates of origin through the "Kimberly Process" to insure all diamonds from
Mills Jewelers are "Conflict Free."