- If you are searching for a round brilliant diamond, ONLY search for “Ideal / Excellent” grade diamonds. Ideal and Excellent are the highest cut grade obtainable from AGS and GIA, respectively.
- Whenever available, use the certificate’s cut grade over and above the retailers branded cut grade (i.e. Astor by Blue Nile)
- Whenever possible, leverage an IdealScope – a diamond cut grade tool which showcases light returned (i.e. see red hearts and arrow images). The more light returned, the better the diamond’s cut.
- A smaller ideal cut diamond returns more light than a slightly larger diamond of lesser cut quality and may look larger to the naked eye.
- Focus on buying a well-cut diamond. It will have more life and sparkle than one of lesser cut quality.
Examples of Real Cuts
Before we get into the science around cuts and how they affect light performance, have a look at the 3 diamonds below. Each diamond has a different cut and exhibits a different behaviour in terms of sparkle and liveliness. Click on any image and use the 360 view to see how each diamond performs.
The shallow cut diamond is larger (at 6.64 x 6.55mm) but looks glassy and lifeless without any sparkle. The deep cut diamond is smaller (6.17 x 6.21mm) and exhibits a lack of sparkle in the center. The ideal cut diamond is what we’re after with brilliance and sparkle all around.
Why is a diamond’s cut so important?
A diamond’s cut greatly influences its allure and brilliance. A well cut diamond exemplifies a high degree of brilliance, sparkle and liveliness thanks to a high percentage of light being returned from the pavillion (bottom of the diamond) back to your eyes. Cut poorly, the same diamond may exhibit less luminosity and appear lifeless due to light being leaked.
When a diamond has a high quality cut (ideal cut), incident light will enter the stone through the table and crown as shown above and travel toward the pavilion where it reflects from one side to the other before bouncing back out of the diamond’s table toward you. This phenomenon is referred to as “light return” which affects a diamond’s brightness, brilliance, and dispersion. Any light-leakage caused by poor cutting, will reduce the amount of light returned, and how good the diamond looks.
When jewelers judge the quality of a diamond cut, a lot of times they rate it as “The most important of the 4 Cs”. Diamond cut is regarded so highly as it actually influences the other C’s.
- TIP: The better a diamond’s cut, the more difficult it is to discern its color grade
- TIP: The better a diamond’s cut, the larger the diamond will appear (relative to a similar diamond with lesser cut grade)
What this means for the average shopper is that buying a diamond with a high quality cut will yield you a high quality diamond, regardless if the color or carat weight are of a lesser grade.
Why different diamond cut grades exist
The way a diamond is cut is primarily dependent upon (1) the original shape of the rough stone, (2) location of the inclusons and flaws to be eliminated, and (3) the preservation of carat weight. Diamond cutters always apply a cut which will maximize the value of the diamond when completed.
How diamond cut grades are assigned
A diamond’s cut is evaluated by trained graders who assess a stone’s symmetry and proportions and assign a cut grade based on how closely the diamond matches the particular “ideal” cut used as a benchmark. The closer the diamond matches to the ideal benchmark, the higher the cut grade.
Diamonds are assigned a cut grade based on a number of factors namely proportion, craftsmanship and light performance. No standard cut grading scheme exists so grading scales will vary between retailers and institutions. The most common cut grade used are GIA and AGS and are as follows:
- Ideal (AGS highest cut grade obtainable)
- Excellent (GIA highest cut grade obtainable)
- Very Good
Branded Ideal Cuts from popular retailers:
Many online diamond retailers have their own branded ideal cut diamonds. As each retailer will have their own criteria into what passes for their signature ideal, it is difficult to compare one brands signature ideal to another brands signature ideal. For this reason, always refer back to the cut grade on the certification (GIA / AGS).
Diamond Cut vs. Diamond Shape
For clarification, diamond cut grade is not to be confused with a diamond’s SHAPE (round brilliant, oval, princess,). Diamond cut grading rather refers to the symmetry, polish, and overall proportions of a diamond. Cut does not refer to shape (pear, oval), but rather the outward appearance, cut of the facets, symmetry, polish and all other aspects of a diamond that makes it scintillate.
The cut of a diamond greatly impacts a diamond brilliance, this means if it is cut poorly, it will be less luminous. A diamond cut too shallow lacks in brilliance giving it a very cold appearance. In contrary, diamonds cut too deep will appear dark.
When starting your search for a loose diamond, don’t be skimpy on cut. We recommend not going below a cut grade ‘Ideal (0)’ for AGS and ‘Excellent’ for GIA. The reason is this: a well cut diamond will appear larger than a poorly cut diamond. What this means is that a .9 carat diamond with Excellent cut will appear larger than a 1-carat diamond with good cut. This means money saved (as there is usually a premium on 1-carat diamonds and above).