Diamond Cut Quality

If you’re searching for the perfect diamond, then please contact me, and let me know your budget and what you’re looking for. I’ll sift through hundreds of thousands of diamonds online from vendors like James Allen and Blue Nile, and find the perfect stone for you and your budget. Unlike the other sites, I’m not looking to sell you anything – my advice is objective and in your best interest.  You have nothing to lose and a larger diamond or saving hundreds of dollars to gain.

Bottom Line Recommendation:

  • Diamond Cut Grade: For GIA Certified Diamonds, a cut grade of “Very Good” will look great.  You will, however, be able to notice an improvement in brilliance by upgrading to “Excellent.”  For AGS Certified Diamonds, a cut grade of “Excellent” will suffice, but you will notice added brilliance by upgrading to “Ideal”
  • “Triple Excellent” or “Triple Zero” look pretty on paper, but you shouldn’t pay extra for Excellent (or AGS Ideal) Polish or Symmetry.  You cannot detect the difference between Good (AGS Very Good) Polish and Symmetry and Excellent (AGS Ideal) Polish and Symmetry with your naked eye.  In most cases you need a microscope to detect the difference.
  • For Round Brilliant Cut Diamonds, don’t give too much credence to an online vendor’s cut grade.   Only focus on the GIA or AGS cut grade on the certificate.

Diamond Cut – a Definition

Diamond Cut refers to how well proportioned the diamond is.  For example, what percentage of a diamonds diameter is its depth?  What are its various angles and how do they interact with one another?  While these may seem like esoteric questions, these are the essential factors that determine how beautiful your diamond will be.  For a great visual representation of why these issues matter, have a look at James Allen’s page on Diamond Cut.

Diamond Cut Grade — All that Matters

Until January 1st, 2006, you basically had two options when it came to diamond cut grade.  You could either buy a diamond with an AGS certificate and trust their diamond cut grading system, or you could learn about the various proportions of diamond cut and trust your own eduction about what numbers translated into a beautiful diamond.  On that day, though, the GIA introduced a new certificate format that included their very own diamond cut grade.  They claim that their Diamond Cut Grade system is based on 15 years of research testing and retesting different combinations of measurements with real life light performance tests.  ags_ogi_reportAs opposed to the old AGS system which simply defined what an “ideal” diamond is and then gives lower grades the farther away from that “ideal” the parameters are (see table to the left), the GIA system does not have any one single definition of perfection.  They claim that in their research various differing combinations of proportions equally produced diamonds that reflected the most light.  So while in the old AGS model, a diamond with a table size of 60% is automatically penalized to a Diamond Cut Grade of “2,” (on a scale from 0 to 9), with the GIA model, there’s still a chance the diamond could receive an “Excellent” grade if the rest of the parameters are the best possible parameters that combine with a 60% table.

To be fair, in the middle of 2005, AGS also realized that their way of doing things was antiquated.  So beginning on June 1st, the AGS lab began offering its certificates with a new light performance-based cut grade.  As it would turn out, though, this new method made it even more difficult for stones to receive the coveted “Ideal” grade for cut.  Thus, when the GIA cut grade was released a half a year later with its more elegant solution, AGS lost much market share to the GIA.

Realizing their error and almost facing extinction, the AGS lab in 2008 decided to copy the GIA and began offering a “new” proportions based cut grade.  I write “new” in quotation marks because, really, there was nothing new about it.  The AGS cut grade prior to 2005 had always been proportions based.  They simply re-introduced it, just this time with more flexibility. They made the smart decision to mimic the GIA and award Ideal cut grades to different non-concentric combinations of proportions.

In my opinion, the GIA & AGS systems are clearly a much more elegant solution to the question of what cut proportions produce the most beautiful diamonds.  And the fact is, it’s a more elegant solution than your typical diamond dealer’s instincts, as well.  What I mean is, before GIA introduced their cut grade, most diamond dealers thought about cut grade the same way the AGS did.  They had in their mind what was the perfect set of parameters, and basically, diamonds got uglier the further they strayed from that ideal.  This revelation of how GIA Diamond Cut Grade worked was a boon to diamond manufacturers as well.  Now, the cutters had more options when assessing a piece of rough for cutting.  If a diamond with a 57% sized table couldn’t fit into a certain piece of rough and still maintain the weight category, then they could try a diamond with a 60% table and see if that would maintain the weight.

If you have any questions, please post them in the comments below.  I will usually respond within 24 hours.


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  1. Cindy     Reply

    Hello, can you give me your opinion on this diamond:

    GIA 2146268900
    Price: $8,896
    Carat weight: 1.20
    Cut: Very Good
    Color: G
    Clarity: IF
    Depth %: 74.7%
    Table %: 71%
    Polish: Excellent
    Symmetry: Very Good
    Girdle: Thick
    Culet: None
    Fluorescence: None
    Measurements: 5.68 x 5.65 x 4.22 mm
    Length/width ratio: 1.01

    Thank you.

    • Mike     Reply

      The cut looks fine. The price is fine for an IF, but I would find an eye-clean VS to save money.

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