Cut is the most complex and technically difficult factor to analyze.
Contrary to common belief, cut does not refer to shape of the diamond (i.e. oval, pear or round). Instead, a diamond’s cut grade is an assessment of how well it interacts with light and is comprised of factors like polish, symmetry and proportions.
Out of the 4Cs, Cut is arguably the most important C as it has the most significant bearing on a diamond’s physical appearance.
A well cut diamond will exhibit a great balance of these attributes and look breathtaking. In contrast, a poorly cut diamond will resemble frozen spit and look dull. This is why I always emphasize the importance of getting the best cut possible when you are selecting a diamond.
In today’s market, there are many gemological labs that provide diamond grading services for the industry. However, each lab has a slightly different way of representing the cut grade in a report.
To help you understand things better, we are going to explain how cut is represented by 4 of the most well-known labs and take a look at their respective grading reports.
When a gemological lab like GIA evaluates a round diamond for its cut quality, they assess the diamond’s proportions and inspect the diamond visually for its fire, brilliance and scintillation (contrast patterning). Here’s a quick explanation of what the terms mean:
Brightness: Brilliance that results from a combination of white light reflections from the diamond’s internal and external surfaces.
Fire: The way light is dispersed into various colors of the spectrum. It is typically seen as rainbow color flashes and found predominantly in the crown facets area.
Scintillation: Scintillation refers to the sparkle patterning a diamond displays when it is moved or tilted at an angle to the eye (shades of light and dark).
GIA Diamond Grading Report – From January 2006, GIA started to include the cut grading of round brilliants in their reports. This cut grade (on a scale of excellent to poor) is assigned based on a combined assessment of the diamond’s proportions, polish and symmetry.
The full GIA diamond grading report with a clarity plot of inclusions.
The GIA Dossier report is typically used for diamonds less than 1 carat in size.
AGS Diamond Quality Document – AGS was the first independent grading organization to utilize a numerical system in their reports – with 0 being the highest grade. As a diamond deviates further from having ideal light performance, so does the numerical grading value as it starts increasing from 1(Excellent), 2 (Very Good), through to 10 (Poor).
In the AGS report, the following aspects of a diamond’s cut are evaluated: Crown and Pavilion Angle, Pavilion Depth, Girdle Thickness, Table Diameter, Polish, Culet size, Performance, and Symmetry.
Compared to other labs, the AGS cut grading system follows a more scientific approach which provides better objectivity when assessing a diamond’s cut grade. More notably, they subject the diamond to a comprehensive ray tracing analysis and also evaluate the diamond’s light return with the ASET.
IGI Diamond Report – This report contains similar information found in a GIA report but doesn’t include a proportions diagram. The IGI report provides proportion measurements of the diamond in a numerical format and assigns cut grades within a range of Ideal, Excellent, Very Good, Good and Fair.
The five criteria that IGI primarily use for grading a diamond’s cut are: Total Depth, Girdle Thickness, Pavilion Depth, Crown Angle, and Table Width.
Note: IGI grading reports can come in various formats depending on the request.
EGL Report – If you are a consumer intending to make a purchase, stay away from diamonds graded by EGL. EGL is notoriously known for their leniency and lax grading standards.
If you had done some research, you probably found that EGL diamonds are usually priced lower than diamonds graded by other labs like GIA and AGS. However, this does not mean you are getting a good deal.
The truth is, the lower price is reflective of the lower quality diamond it really is. When looking at an EGL report, you can expect to discount 2-3 grades in the diamond’s color and clarity instead of taking the EGL report at face-value.
I don’t recommend buying diamonds with EGL reports as they are often used by unethical jewelers to rip consumers off.
For round brilliants, EGL USA offers the Diamond Analysis Report and issues cut grades within the range of: Ideal Plus – Ideal – Very Good – Good – Fair.
When a cutter is fashioning a diamond from a rough stone, he endeavors to strike a balance between “optimal” cut (which eventually determines appearance) and maximum yield (preserving carat weight from rough stone).
However, the fact that people are willing to pay more for a bigger poorly cut diamond than a smaller well cut diamond puts a lot of pressure on the cutter to preserve weight from the rough stone. Since the value of a diamond is directly proportional to its weight, cut quality is usually compromised for carat weight.
This is the reason why the majority of diamonds are often cut to poor proportions. It is also why you often see diamonds with precise carat weights at 0.70 or 1.00 carat instead of 0.67 or 0.96 since they sell for more!
At this point, I want to go on the record saying that you should only consider buying diamonds graded by GIA or AGS. They are the most consistent labs in terms of their grading standards and offers assurance that the diamond’s qualities have been accurately described.
Next, bear in mind that a diamond’s cut grade is a key factor for consideration when you are making selections. Also, you should note that the lab report isn’t an end all be all solution for selecting the best possible stone.
You see, the grading labs allow diamonds within a range of proportions to fall within their top tier cut category. However, just because a diamond’s proportions fall within “ideal” ranges, it doesn’t mean that the facets interact together as a whole to give the stone optimal light performance.
In order to help you determine this, the easiest method is to use light performance scopes like the ASET and Idealscope for assessment. To find out more, we had dedicated an entire section of the website showing you how to pick a diamond here.
Lastly, I want to share an interesting story with you before I end this article. In a recent trade show I attended, I had the opportunity to speak to people in the management levels from various labs such as EGL, GIA and AGS. I asked them the following question. “Would you buy a diamond graded by your own lab based on a certificate alone assuming that it has the best possible ratings in all aspects of cut?”
The answers were all unanimously: No. Mind you, these are all expert graders in the field and not some unknown John Doe. All of them stated that they either need to look at the diamond in person or require further data before they would commit to a purchase.
The moral of the story here is – you do require additional data beyond a grading report if you want to make rational buying decisions!
Magnified images, video and analytical cut data are provided in White Flash listings.