Diamond Cut Education

The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance.

The width and depth can have an effect on how light travels within the diamond, and how it exits in the form of brilliance.

  • Too Deep: Light escapes out the sides causing the diamond to appear dark and dull.
  • Too Shallow: Light is lost out the bottom causing the diamond to lose brilliance.

 

Cut Determines Brilliance

Determining a diamond's cut grade, however, goes beyond simple measurements of width and depth. Using an optical measuring device, a three-dimensional model is created to determine the diamond's proportions and angles. The interrelations between these various dimensions will greatly affect how light reacts once it enters and how it behaves once it exits; by using sophisticated computer modeling, it is possible to trace light behavior and measure its levels of brightness, fire and scintillation - the face-up appearance.

  • Diameter: The width of the diamond as measured through the girdle.
  • Table: The largest facet of a gemstone.
  • Culet: The facet at the tip of a gemstone. The preferred culet is not visible with the unaided eye (graded "none" or "small").
  • Girdle: The intersection of the crown and pavilion which defines the perimeter of the diamond.
  • Pavilion: The bottom portion of a diamond, extending from the girdle to the culet.
  • Crown: The top portion of a diamond extending from the girdle to the table.
  • Depth: The height of a gemstone measured from the culet to the table.

Polish and Symmetry Affect Sparkle

Polish and symmetry are two important aspects of the cutting process. The polish grade describes the smoothness of the diamond's facets, and the symmetry grade refers to alignment of the facets. With poor polish, the surface of a facet can be dulled, and may create blurred or dulled sparkle. With poor symmetry, light can be misdirected as it enters and exits the diamond. The polish and symmetry grades are clearly listed in each diamond detail page and within the GIA or AGS diamond grading report. For the most beautiful diamond, look for a symmetry grade of excellent (EX), very good (VG), or good (G) for a GIA graded diamond, and ideal (ID), excellent (EX), very good (VG), or good (G) for an AGS graded diamond. Avoid diamonds with symmetry grades of fair (F) or poor (P), as the alignment of their facets may misdirect light so severely that it affects the brilliance of the diamond.

Diamond measurements are calculated and applied to a cut grading scale that makes it easy to understand how well each reflect light:

  • Ideal cut: Represents roughly the top 3% of diamond quality based on cut. Reflects nearly all light that enters the diamond. An exquisite and rare cut.
  • Very good cut: Represents roughly the top 15% of diamond quality based on cut. Reflects nearly as much light as the ideal cut, but for a lower price.
  • Good cut: Represents roughly the top 25% of diamond quality based on cut. Reflects most light that enters. Much less expensive than a very good cut.
  • Fair cut: Represents roughly the top 35% of diamond quality based on cut. Still a quality diamond, but a fair cut will not be as brilliant as a good cut.
  • Poor cut: This includes all diamonds that do not meet the performance standards of a fair cut. These diamonds are generally deep and narrow or shallow and wide and tend to lose most of the light out the sides and bottom.

Which Cut Grade is Best?

Buying a diamond may be one of the most important purchases of your life. For most people, the engagement ring is the first, and surely the most important, diamond they will ever buy. I want to make you get the right one. A Diamond is a commodity when purchased right. There are many grades of diamonds, and each of them has a different value. And also very importantly, Dealers are trying to make as much money from you as they can. Many of these dealers started out as the middlemen in the diamond industry and even though they may sell directly to you they can fool you in many ways. Don’t get fooled. Follow my steps to finding the right diamond within your budget and get a great value at the same time.

Here you go.

  • #1 Budget - Know what you are willing to spend and stick to it.
  • #2 Expectations - Listen to her. Try to understand her that her expectations are so that you don’t feel so over whelmed. Also you will need her left hand ring finger size.
  • #3 When – Give yourself enough time to learn about the diamond and ring design so that you can plan the perfect proposal.

Looking for the right diamond. Note my information sources are GIA & AGS.

ROUND SHAPE AND THE BEST CUT

  • TABLE % TO BE GIA 52-58%             AGS 52.4-57.5%
  • CROWN ANGLE GIA  33% or more     AGS 33.7-35.8%
  • GIRDLE THICKNESS GIA Thin to Med AGS Thin,Medium Slighty Thick
  • PAVILION DEPTH GIA 42-44%           AGS 42.2-43.8%

PRINCESS SHAPE

  • LENGTH TO WIDTH RATIO 1.00 THROUGH 1.10 TO 1 RATIO
  • TO CALULATE LENGTH TO WIDTH RATIO OF FANCY CUT DIAMONDS, YOU SIMPLY DIVIDE LENGTH BY WIDTH.
  • FOR EXAMPLE, 4.8mm by 4.7mm =1.02

OVAL SHAPE

Note you want very little or no BOW TIE

  • LENGTH TO WIDTH RATIO 1.30 THROUGH 1.60 TO 1 RATIO
  • TO CALULATE LENGTH TO WIDTH RATIO OF FANCY CUT DIAMONDS, YOU SIMPLY DIVIDE LENGTH BY WIDTH.
  • FOR EXAMPLE, 6mm by 4mm = 1.5

PEAR SHAPE

  • LENGTH TO WIDTH RATIO 1.40 THROUGH 1.75 TO 1 RATIO
  • TO CALULATE LENGTH TO WIDTH RATIO OF FANCY CUT DIAMONDS, YOU SIMPLY DIVIDE LENGTH BY WIDTH.
  • FOR EXAMPLE, 7mm by 5mm = 1.4

MARQUISE SHAPE

  • LENGTH TO WIDTH RATIO 1.75 THROUGH 2.25 TO 1 RATIO
  • TO CALULATE LENGTH TO WIDTH RATIO OF FANCY CUT DIAMONDS, YOU SIMPLY DIVIDE LENGTH BY WIDTH.
  • FOR EXAMPLE, 11mm by 5.5mm = 2

RADIANT SHAPE

  • LENGTH TO WIDTH RATIO 1.20 THROUGH 1.50 TO 1 RATIO
  • TO CALULATE LENGTH TO WIDTH RATIO OF FANCY CUT DIAMONDS, YOU SIMPLY DIVIDE LENGTH BY WIDTH.
  • FOR EXAMPLE, 6mm by 4mm = 1.5

EMERALD SHAPE

  • LENGTH TO WIDTH RATIO 1.30 THROUGH 1.60 TO 1 RATIO
  • TO CALULATE LENGTH TO WIDTH RATIO OF FANCY CUT DIAMONDS, YOU SIMPLY DIVIDE LENGTH BY WIDTH.
  • FOR EXAMPLE, 8mm by 6mm = 1.33333333