The cut of a diamond is by far the largest factor that determines its beauty. The better the cut, the better the brilliance and sparkle of the diamond. If the stone is cut is too deep or too shallow, light that enters the diamond will leak through it. This is why poorly cut diamonds often look darker and lifeless.
Cut is said to be the most important C as it has the greatest bearing on the gem’s appearance. Personally, I fully agree with this statement. After all, why would you even want a diamond that is dull and resembles frozen spit?
Cut grade is the objective assessment of the gem’s proportions and finishing. In grading reports, the cut grade is assigned as a combined rating of these 2 aspects. Using the GIA system as an example, diamonds can be classified into various grades such as Excellent, Very Good, Good, Fair, and Poor. As much as your budget allows, you should ALWAYS strive for a better cut grade in a diamond.
Ok, I know you are probably thinking… “Why are you telling me this? I know that cut is important. As long as I choose a GIA triple excellent diamond, wouldn’t all my problems be solved?”
Here’s what most people don’t know. While the GIA grading system can provide a fairly good assessment of the diamond’s brilliance, GIA also allows a wide range of proportions to exist within their triple excellent ratings.
This means that 2 diamonds with GIA triple excellent ratings might not necessarily look and perform the same. Ultimately, the subtle differences in proportions and facet alignment will affect the stone’s interaction with light.
To help you decide which diamond has better performance, you need to go beyond what the grading report says and perform a deeper analysis.
When you are looking for diamonds cut for performance, the proportions (down to every 0.1° or 0.1%) matter because of light physics. Even if a diamond has the slightest deviation in angles (e.g. a 41.2° pavilion angle), it WILL impact light performance adversely.
As mentioned in the earlier section, grading labs like GIA allow a broad spectrum of proportions and varying degrees of light performance. The fact is, most cutters know this and consciously cut diamonds for maximum carat weight yield instead of performance.
The following table of proportions is designed to help you filter out the mediocre diamonds that reside within the GIA 3Ex grading range.
Follow these proportions guidelines when shortlisting diamonds.
|Table %||54.0% to 57.0%|
|Depth %||61.0% to 62.5%|
|Crown Angle||34.0° to 35.0°|
|Pavilion Angle||40.6° to 41.0°|
|Lower Girdles||75% to 80%|
|Star Facets||50% to 55%|
|Girdle Thickness||T – M – ST|
Before you get too carried away by numerical numbers, there’s something you need to be absolutely clear about. I will re-emphasize: this table of proportions is meant to be used for weeding out poorly cut diamonds. Just because a diamond has proportions that fall into those stated above doesn’t make it an auto-pick.
Why? Even if 2 diamonds has similar proportions on paper, they would still handle light differently in real life. The objective of filtering and eliminating diamonds via their proportions would leave you with a manageable number of diamonds for further investigation.
So, what’s next after you narrow down your initial selections based on the ideal proportions above? How do you take the analysis of your shortlisted diamonds to the next stage? Thankfully, there is a simple tool called the Idealscope which allows you to determine a diamond’s optics in an objective manner.
Find out more on the next page…