Shopping Cart (0)
My Diamonds (0)
My Jewelry (0)
My Diamond Pairs (0)
Last Visited Products
By  , Tuesday, July 25, 2006


It’s important for buyers to know that aspects of the 2006 GIA diamond cut grading system are skewed to favor mass manufacturers over consumers.   

GIA performed studies for 15 years then enlisted human diamond observations.  Problems arose when only 58% of the human results correlated to their prior research:  Those observations were made primarily by trade people and demonstrate a bias towards mass manufacture and mass sales.  GIA adapted their prior research to accommodate the trade observations.  The result is a system which favors mass manufacturers over consumers. 

Are all GIA EX diamonds bad? 

The system uses external measurements (proportions) to predict how well a diamond will sparkle and reflect light internally.  Some proportions sets agree with proven systems. 

What should the diamond buyer beware? 

(1) The width of the EX grade, (2) abundant steep/deep combinations.  Also, be aware of the ‘rounding’ that occurs on GIA diamond grading reports; the angles you see are not reported to the tenth of a degree like AGS reports or Sarin/Helium scans.  There are other issues, but these are the main ones to look out for when considering a GIA ‘EX.’ 



Using the proven AGS 11-level system for comparison, GIA’s top grade is extremely wide.  Alone, it spans the top 5 AGS grades.  A diamond graded GIA Excellent may be an AGS4 as easily as an AGS0.   Further, each lower AGS grade leads to extra weight within the same GIA grade.  Mass manufacturers will cut the heaviest possible GIA Excellent.  This means when a consumer is buying a GIA Excellent the statistical chance of him buying an AGS4 will be high.  GIA may tell you that within their top grade there is no visible difference but AGS will tell you it can be divided into 5 different grades. 

EXAMPLE A:  Wide EX grade

  • 57t 62.9d 35c 41.6p 45s 80lh m-st vg/vg (GIA-rounded)
  • Equivalent to AGS2
  • Received 'Very Good' symmetry - but has an extra facet plotted on the crown
  • Even worse combinations are allowed







Steep/deep is positive for manufacturers but negative for buyers.  As the diamond is made steeper weight is added and spread is reduced, so the diamond looks smaller than it should for its carat weight.  Steep/deep combos also leak light so performance is reduced.  Very steep/deep entraps body color, so a diamond graded F may actually appear like a G or H. 

EXAMPLE B:  Light leakage and reduced performance 

GIA Excellent - the same diamond as in Example A.  There is enough light leakage that the holder’s finger can be seen through the table of the stone.

  • ASET, On Finger, Ideal-Scope (below)



  • Actual IS, simulated IS and cut quality estimate (below)
  • From dmc file:  56.8t 62.9d 35.28c 41.44p dmc file
  • GIA Sarins should have rounded to 41.4 and 35.5 rather than 41.6 and 35 (?)



For more specific questions ask our experts
Live chat by BoldChat

Continue shopping at

  • Follow Us
  • Sign up for our Newsletter:
    Whiteflash rating :
    4.80 Rating based on 4251 reviews. Read all testimonials
  • Contact Us
    Give us feedback Give us feedback
    Telephone 1-877-612-6770
    Outside USA 1-832-252-6770
    2150 Town Square Pl
    Sugar Land,
    TX 77479 USA
    Winner of the 2015 BBB Pinnacle Award
    Best Jeweler in Houston, Texas

Welcome to Whiteflash!

We cordially invite our Houston area clients to visit our beautiful boutique style showroom for a very special experience. Come see our A CUT ABOVE® diamonds and designer engagement rings in person and meet our friendly and knowledgeable staff of jewelry professionals.

Book your appointment now by visiting our Showroom Page where you can schedule your visit and learn more about the special venue we have created for our Houston area clients