In the world of round diamonds, a stone that scores an excellent rating in all three aspects (3Ex) of polish, symmetry and cut is often considered to be the pinnacle of well-cut diamonds. In fact, consumers with a better awareness of cut tend to buy diamonds specifically within the triple excellent (3Ex) standards.
It's no coincidence that jewellers make use of the GIA triple excellent "branding" to market their inventory and charge a higher premium for such diamonds. However, one common misconception consumers have is that as long as they buy a GIA triple excellent diamond, they will be getting the most brilliant and most well-cut diamond.
The truth is, most jewellers and sales staff mislead consumers during a pitch just to close a sale. Diamonds are NOT created equal. A diamond with 3 excellent ratings in a GIA lab report doesn't necessarily mean that it has the best possible optical performance nor does it mean that it is the best looking diamond.
If you buy a GIA triple excellent diamond, you definitely won't get an "horrible" looking stone. This is because each diamond has to pass through a visual inspection for fire, brilliance and scintillation during the GIA grading process.
Instead, it now becomes a matter of how precise the diamond is cut and the degree of light performance the diamond has. In this regard, a lab report by itself will not tell you anything meaningful when you make comparisons between 3Ex diamonds:
Did the diamond barely made it to an excellent cut grade?
Was the diamond cut so well that it sits on the zenith of the excellent grade?
An in-depth analysis to explain why the above examples fail to meet the criteria, are shown below:
Well-cut diamonds look bright because the facets position themselves to handle and return light to the viewer's eye.
When choosing a round brilliant cut diamond, you need to place emphasis on the angles and proportions as they play a huge role in determining optical performance. Steep pavilion angles (> 41.0 degrees) will usually cause light leakage beneath the table facet. To illustrate this, look at the idealscope image of the diamond below:
An idealscope is a simple and portable tool that anyone can use to analyze a diamond's light performance. The red areas represent light return while the white areas indicate light leakage which is undesirable.
Unlike steep pavilion angles example, a deeper cut diamond that has a depth percentage of 63.0% or more will mean that you get a smaller looking stone since its weight is hidden in the profile view.
Also, deeper cut diamonds tend to exhibit light leakage under the table as indicated by the idealscope image below:
Taking a closer look at the third diamond in its face up view. Note that this GIA diamond had been assigned the highest rating (excellent) in its symmetry grade.
How can a diamond with an excellent symmetry grade look like this? It doesn't even show a symmetrical patterning at all! Even for a layman, it's obvious there is an uneven contrast patterning across the diamond. Why is this so?
The truth is, GIA grades diamonds in controlled environments and lighting conditions under 10X magnification. In the lab, the grades in which a diamond can be assigned will have a range of tolerances. This means even if a diamond achieves the highest grade of excellent, it doesn't mean it is "perfect".
In reality, a diamond with an excellent symmetry rating can still have slightly misshapen facets or misaligned facet junctions. When these minor deviations add up, it can result in a slightly wonky appearance as seen below.
Compared to the earlier diamonds, this idealscope image shows only a little light leakage. However, the unpleasant scintillation pattern this diamond displays makes it a poor choice. This is a classic example of a diamond that barely makes it into the triple excellent ratings and also shows you why buying blind is a bad idea.
To most people, buying a diamond involves significant financial and emotional investments. Everyone wants to get the most sparkly and beautiful diamond for their budget. As a benchmark for you to do comparisons, the following diamond is an example of a truly well-cut diamond, with perfect hearts & arrows (H&A).
Did you know that the information found in this guide is actually facts that most jewellers would never share with you for a couple of reasons?
One, most jewellers don't have a good understanding of cut mechanics themselves. How would you expect them to properly advise you when they can't even comprehend these things themselves? Don't be surprised by the amount of jewellers and sales people who have poor knowledge of cut despite being in the trade for years.
Two, truly well cut diamonds are rare. Even if the occasional jeweller has indepth knowledge about cut, most would never tell you about the true performance of their diamonds. Why? The more you begin to understand cut, the more their inventory would appear inept and inferior.
Most jewellers are in the business of making money even if it is done at the expense of the consumer. It won't make sense for jewellers to place themselves in your perspective and risk losing a sale by over-educating you.