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DIAMOND CUT REVIEW 

Matt Ubertini GIA Gemologist At DreamStone

By Matt Ubertini
Staff Gemologist

Matt has a vast experience working with top diamond manufacturers and jewelers in NYC's diamond district for over 18 years. With graduate gemologist degrees from the Gemological Institute of America and International School of Gemology, Matt uses real world examples to help simplify the understanding of diamonds.  



The diamond cut grade refers to the cut quality of the diamond and can be as straight forward or as complicated as you want it to be. In a nutshell it is how a diamond cutter polishes the facets of a diamond.  The aim is to angle the facets in such a way where they act as mirrors channeling the light that comes through the top of the gem and returning it back out the top to your eye. As the diamond refracts the light it splits the rays just like a prism so that you can view the incredible rainbow of colors hidden within visible light. This is what people refer to as a diamond having “life”, “fire”, or “sparkle.” If this sounds like an important attribute, it is in fact the cut grade of a diamond and is just as important (some might argue the most important) factor out of the 4’C’s because it exhibits the “brilliance” of a diamond. The good news is over 1/2 of the diamonds today are cut to “ideal” proportions.  Often times, you don’t even have to pay a premium for them either.

Here are the cut grades provided by GIA accompanied by images:

 

 

DreamStone Ideal

Excellent

Very Good

Good

Fair

 

ROUND DIAMOND CUT GRADE

The first thing you should realize is that round diamonds are the only shape that GIA provides a cut grade for and it was added to the grading report only in the last 15 years. All the other shapes, called “fancy” shapes, do not have a dedicated “grade” for cut on the GIA grading report. The reason for this is because the round shape being a perfect (or close to perfect) circumference means that regardless of the diamond’s depth, or table, the round shape will always be, well… precisely round and therefore will adhere to one of the universal proportions for each cut grade. Other shapes like cushions, ovals, princess cut, radiant, emerald, marquise, asscher, etc..  can vary dramatically in ratio and overall make and so you can have two completely different styles within the same fancy shape. With that said, there are well established industry standards for what is considered “poor”, “good”, and “very good” for some of the fancy shapes. We just don’t have any unbiased third party labs to keep things consistent across the board so every retailer may tweak the measurements a little differently to come up with their own cut grade for fancy shapes.

RECOMMENDED RANGES (FOR ROUND DIAMONDS)

  • Depth percentage between 63%-59%
  • Table width percentage between 60%-54%
  • Crown angle between 35%-33%
  • Star length of 50%
  • Girdle of 4%-2.5%
  • Girdle thickness of thin to thick, thin to medium, medium to medium, medium, or medium to thick
 

IDEALSCOPE & ASET TOOLS

Here is where the whole cut grading business can get a little hairy. Remember that the cut grade is an overall summary of how well a diamond is cut and from a practical standpoint you can stop right there and be happy as can be with your choice of cut grade. For those who want to step further into the abyss, you’ll discover a whole new topic called “light performance.” Laboratories in the diamond industry have developed tools that are supposed to give you indications of a diamond’s brilliance, light return, and leakage as well as contrast and scintillation. Idealscope and ASET (Angular Spectrum Evaluation Tool) are two examples of simple tools that have gained popularity online with websites displaying colorful static snapshots of the actual diamond taken with one of these tools. There is a plethora of information on the internet filled by armies of blog and forum contributors about this topic, but what you’ll end up discovering is that there is no unanimous agreement among any of them. One person may swear by one tool and another may promise the world with another. Although Idealscope and ASET are different devices, they basically try to accomplish the same goal. Both are lens encased in a bright colored reflector with a viewing hole. This creates a controlled light environment for the observer to see. They may be used as a simple optical symmetry grading tool to view the Hearts and Arrows in a diamond or advanced users can try to gauge the amount of fire a diamond might have. What neither of these tools can do is tell you anything about a diamond’s carat, color, or clarity. More importantly, neither can measure a diamond’s true sparkle and beauty. They are at best one additional layer for those who insist on using some basic scientific gadget to gain insight into these twinkly little objects.

MARKETING VERSES VALUE

I think the industry has gotten carried away with the terminology for premium cut diamonds.  There are countless companies claiming the crown for the nicest cut diamonds and label them with ever convincing names. There is a definite portion of what I see as pure marketing to set apart one brand from another promising that their formula guarantees the most brilliance. There is no doubt that GIA’s “excellent” cut grade is too broad and within the spectrum of “excellent” cut diamonds there is a narrower range of measurements that would be more desirable, but sometimes the branding dresses up what is just typical ideal cut diamond so don’t get too excited by the cool names.

SPARKLE & BEAUTY IS SUBJECTIVE

For decades a diamond’s cut was considered subjective and while technology improved to offer us a set series of numbers to determine the cut grade of round diamonds, I think there is still a bit of subjectivity left to enjoy. There are some online tools available that take a diamond’s crown angle, girdle percent, and depth pavilion among other factors to yield a score for the diamond’s scintillation and sparkle. I’m not a huge fan of these tools and its not because there is anything wrong with them, but rather that they cause users to be fixated on the trivial.  The benefit of a perfect score verses near perfect score is something you can hardly appreciate with the naked eye and as I mentioned earlier could cause you to jeopardize on another important factor just to meet the criteria of some particular calculation. It also robes you of personal preference. One algorithm may favor smaller tables in the 53-57% range while I personally love bigger tables in the 59-60% range.  It allows you to see all the facets clearly and to my eye its just a more pleasing visual affect. When I compare it to a 54% table it just doesn’t do it for me. I prefer to have a slightly larger window into the diamond. The point is these online tools have pre-set figures developed by someone else’s expert opinion and while one mechanism tests results lead you to one place, another may lead you to a different set of results. What new technology will come along tomorrow that will try to tell us they have discovered the holy grail in diamond brilliance?

Once a diamond is considered “excellent” cut by GIA, the brilliance factor is already within 90% of the best preforming brilliance possible. If you take it a step further and fine tune your selection to say Excellent Cut, Excellent Symmetry, and Excellent Polish, and stay within the recommended ranges for table and depth, you’ll get even closer to maximum brilliance. Beyond this point is diminishing returns. Trying to hunt down a diamond with the best score that some online tool suggests can greatly limit your options. Imagine you were taking a test that was divided into 4 sections, math, reading, writing, and verbal, each section represented 25% of the overall score. Would you want to score 100% just on math, and only 50% on reading?  The same goes for the 4C’s, if we divide, cut, color, clarity and carat weight each with the same 25% importance factor of the overall diamond, and you found a diamond that has an “excellent” cut grade akin to a 90%+ score for cut and you have everything else you wanted to go with it in the carat, clarity, and color department why would you forgo this option just to find another diamond with an infinitesimal higher degree in cut score and compromise on something else?

CONCLUSION

Go for a excellent cut grade and take all the chatter about light performance with a grain of salt. You can easily fine tune your search to diamonds with excellent cut grade that also have excellent polish and excellent symmetry and still have plenty of results.  As far as limiting your results to specific range of tables, depths, crown angles, pavilion depths, girdle percentages, knock yourself out as long as these details don’t cause you to forgo other attributes that are important to you. But, narrowing your search to an even smaller pool of numbers within these recommend ranges for the best cut diamonds just to chase after score could cause you to miss another mark.





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