Cut: A Diamond’s Most Important Value Factor

"I saw the angel in the marble and carved until I set him free." - Michelangelo

A diamond cutter is like a sculptor.  He has a piece of rough diamond in front of him, and he must envision the finished diamond.  He asks himself many questions: What shape diamond will best fit this piece of rough?  Should I cut the rough into one larger diamond and sacrifice cut quality, or should I cut two diamonds of smaller size but of finer cut quality?  How can I maximize the value of the finished diamond(s) that will come from this piece of rough?  This planning stage can take days, weeks, months, even years if the piece of rough is of great importance.  He polishes a window to see into the stone, and he looks for the angel within.

Cut is the Most Important Human Contribution to a Diamond's Value

Unless a diamond undergoes treatments in a laboratory, man cannot change the color or clarity of the diamond rough.  He can just cut around inclusions and work to minimize the impact of a rough diamond's color.  The diamond cutter, however, has complete control over the cut of the diamond.  If he has a colorless, flawless rough diamond and cuts it to poor proportions, the diamond will be lifeless and dull.  But if he cuts the diamond to more exact, precise proportions with a fine finish, the angel will be set free from within the diamond.

Factors Affecting the Cut of a Diamond

There are many important factors in a diamond's cut that are precisely measured and weighed against carefully determined guidelines.  Round brilliant diamonds are the only diamonds that receive a final cut grade through the GIA cut grading system.  Polish and symmetry grades are given on all diamond cuts.  Here is a list of those factors that you will most likely come across:

  • Table size
  • Total depth percentage
  • Crown height
  • Crown angle
  • Star facet length
  • Girdle thickness percentage
  • Girdle thickness verbal description
  • Pavilion depth
  • Pavilion angle
  • Lower girdle facet length
  • Culet size
  • Polish
  • Symmetry

Each one of these factors has many different possible values that are considered in order to end up at the final cut grade.  They are all weighed equally with the exception of polish and symmetry.  Polish and symmetry grades are bumped up one grade when determining the diamond cut grade.  For example, a diamond can receive a GIA Excellent cut grade and have Very Good polish and symmetry grades.

Value of a Diamond

So how is that you can have 10 1.00-carat, G-color, VS1-clarity, round brilliant diamonds all graded by GIA and they each have different values (read: prices)?  The cut grade is most likely the answer.  All other factors being equal, a diamond with an Excellent cut grade is worth far more than one a lower cut grade.  These diamonds sell at a premium because they are the most coveted round brilliant diamonds.  A well-selected diamond with a Very Good cut grade can also be a great value, as usually there is one cut factor that through off the grade.

To maximize your diamond budget while getting the most beautiful diamond you can, I recommend a GIA cut grade of Excellent or Very Good.

Originally posted by me to on 4/6/2010.

Leave a Reply