Reading Diamond Certs :: Crown Angle

The Crown Angle in the diamond below is shown on the left, indicating 34.5 degrees.


These numbers are significant because they determine a lot of how the light that enters the top of the diamond will :

  1. enter the diamond through the crown
  2. reflect off of pavilion facets and travel within the diamond
  3. reflect back up to the eye, or…
  4. refract through the crown and disperse into the colors of the rainbow

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If these angles are not correct, the light will not reflect and refract properly, and the light performance will decrease.

In recent years, it has been determined that there is a range of crown angles that can be acceptable, even ideal, depending on the other angles and proportions of the diamond. The real factor is how everything works together, and never just about one number or measurement.

To give you an idea of how everything works together, here is a chart from the GIA website that tracks how the table %, pavilion angle, and crown angle interact to create the most beauty, as indicated by the EX (excellent) cut grade. Note these are all based on the fact that the other major factors are all kept precisely constant, namely… star facet length (55%), lower half length (80%), girdle thickness 3.0%), polish (VG or EX), symmetry (VG or EX), girdle min/max (THN-STK), culet size (NON-SML), and painting or digging out (none to negligible). Variations in any of these could result in a different cut grade.

Sample GIA Cut Grade Estimation Table(Click Image To Enlarge)

These charts show that a diamond can have a crown angle from all the way down at 26.5 degrees, all the way up to 38.5 degrees, depending on table and pavilion, and still have amazing light performance… enough to earn the Excellent cut grade from GIA!

You can also see the full set of GIA Cut Grade Estimation Tables.

These charts are also a factor in the GIA Facetware Cut Estimator.

Cut Grade Makes It Simple

This is very complicated stuff, but it can be very simple. Pay attention to the Cut Grade. When you look at the cut grade, you know how everything works together, and numbers like the crown angle are less important by itself. Therefore, always give the greatest weight to the cut grade, to know what the experts think about the overall Light Performance by measuring. Guessing from the crown angle will not be sufficient to know the beauty of the diamond.

NEXT :: Diamond Certificates :: Pavilion Angle

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