Monday, August 3, 2015

Circular Brilliant Cut Diamonds

Circular Brilliant Cut is a new name for an antique stone. You've likely heard of the popular antique nomenclatures Old Mine and Old European (Old Euro) diamonds. You've also probably heard of the ubiquitous Transitional Cut. However, unless you pay very close attention to the buzz about GIA gemstone grading, you might not have heard of the Circular Brilliant Cut.

Prior to late 2013, this cut did not have parameters associated with it. Circular Brilliant Cut stones would have been labeled as transitional, and if graded by the GIA on the Cut Scale, would have received a "Fair" or even a "Poor" grade.{1}

Under pressure from dealers who felt these antique stones were being "judged by standards that they were never fashioned to meet," the GIA agreed to create a new category, which they named the Circular Brilliant Cut.{2}

The parameters for a diamond to qualify for this new cut grade are as follows (adapted from Duncan Pay's article dated December 20, 2013 on the GIA blog):

  1. The lower half length of the stone must be less than or equal to 60%.
  2. The star length must be less than or equal to 50%.
  3. The culet size must be medium or larger.
All three requirements must be met for a diamond to qualify. 

As a comparison, Old European Cut diamonds, which are also eligible for a cut grade on a GIA grading report, must meet the following criteria (adapted from the same article in 2013):
  1. The table size must be less than or equal to 53%.
  2. The crown angle must be greater than or equal to 40 degrees.
  3. The lower half facet length must be less than or equal to 60%.
  4. The culet size must be 'slightly large' or larger.
Before the advent of the new Circular Brilliant Cut, a diamond which fell outside the parameters for an Old European or Old Mine cut, were compared, typically unfavorably, against the parameters of a Modern Round Brilliant Cut. These parameters are as follows{3}:
  1. The lower half facet length must equal 80%
  2. The star length must equal 55%.
  3. The culet size should be 'NON' to small.
Perhaps you have or plan to purchase a transitional cut diamond that has been previously graded (prior to 2013) as 'poor' or 'fair', or which does not have a cut grade listed on your GIA report. If that is the case, may we recommend contacting the GIA to inquire as to whether your stone might qualify for a reevaluation according to these fairly new Circular Brilliant Cut guidelines?

~Angela Magnotti Andrews, Staff Writer


  1. Pay, Duncan. "Describing 58-facet Round Brilliant-Cut Diamonds at GIA," GIA Blog, December 20, 2013.
  2. Ibid.
  3. "Estimating a Cut Grade," GIA Grading System, accessed July 24, 2015.

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