Cut is a vital characteristic of any diamond, determining how well its facets capture and reflect light. A well cut diamond will sparkle with the brilliance and fire diamonds are famous for, while a poorly cut diamond may appear lifeless, even if highly graded in colour or clarity.
In this guide we’ll outline how cut is graded, and explore why cut makes diamond jewellery dazzle…
What is diamond cut?
Although you might hear phrases such as ‘pear cut’ or ‘emerald cut’ diamond, when it comes to the 4Cs, cut refers to how well a diamond has been shaped and faceted from its raw form. When a diamond is expertly cut, light enters through the top, bounces around inside and exits through the top again - a process called refraction. This is what gives diamonds their incomparable sparkle and life.
The secret to a well cut diamond is proportion. For round brilliant cut diamonds, there are defined ideal proportions. The closer a diamond adheres to these parameters, the better its cut.
How is diamond cut graded?
Diamond cut is graded on a scale from Excellent to Poor, with proportion, symmetry and polish determining how the cut is graded. The better these elements work together, the more light the diamond reflects.
What effect does diamond cut have?
A diamond’s brilliance is almost entirely a product of its cut. The more precisely cut the angles and facets, the more light the diamond will reflect. This refraction of light is what creates that eye-catching sparkle that diamonds are famous for.
A well-cut diamond demonstrates three qualities:
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Brilliance: bright, white light reflected internally and externally
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Fire: flashes of rainbow colour
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Scintillation: vibrant sparkling when the diamond moves
Together, these qualities are what make diamonds so unique. No other stone, however it is cut, will glitter the same way a diamond does. On the other hand, even a beautifully clear and white diamond will not sparkle well if cut badly. A poor cut allows light to escape from the bottom or sides of the diamond, lessening the brilliance.
How diamond cut is graded
Only round brilliant cut diamonds have an official grading for cut, based on a scale developed by the GIA (Gemological Institute of America). The scale covers:
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Excellent
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Very Good
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Good
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Fair
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Poor
An Excellent cut diamond will reflect nearly all the light that enters it, creating beautiful brilliance and sparkle. A Poor cut allows much of the light to leak out, causing the diamond to look dim or glassy.
At Harper Tait, we sell only Excellent and Very Good cut grades, ensuring that every diamond you buy from us sparkles to its full potential! At grades Good and below you will begin to visually see a difference in the sparkle of your diamond - and that’s a disappointment best avoided.
How is cut grade determined?
An expert diamond grader will determine a diamond’s cut based on its visual brilliance, fire and scintillation, as well as four other parameters:
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Ratio (or proportion)
For every RBC diamond there are set proportions that indicate a well cut diamond. Displayed in percentages (see image), the ratio shows how each part of a diamond relate to one another.
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Durability
If a round diamond’s girdle is too thin it may be susceptible to damage. A high cut grade is your protection against this risk, downgrading stones will a too-thin girdle.
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Symmetry
Symmetry refers to how balanced and uniform the diamond is.
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Polish
The final process of cutting a diamond is its polish. A well-polished diamond has a smooth and even surface, ensuring nothing obstructs the flow of light through the facets.
The diamond shape vs diamond cut
Although only round brilliant cut diamonds have an official grading, cut impacts all diamond shapes. Whether a brilliant cut or step cut, the precision and balance with which a diamond has been cut makes a real difference to its appearance and sparkle.
Each diamond shape has its own individual priorities when it comes to cut. For instance, symmetry is particularly important in a princess cut. That’s where our expertise comes in…
We hand select all our diamonds, looking at how they perform visually and their recorded proportions. Whatever shape you choose, only beautifully cut diamonds end up in our engagement rings!
Diamond Cut FAQs
Why is diamond cut considered the most important of the 4Cs?
While the other Cs (colour, clarity, and carat) matter, cut has the biggest influence on how a diamond looks. Diamonds are famous for their sparkle - and for this, a diamond must be well cut, regardless of its size, colour or clarity.
How does diamond cut impact price?
Higher cut grades like Excellent and Very Good naturally increase a diamond’s price, but the difference is worth the investment. We almost always advise compromising on another characteristic, such as choosing a smaller carat weight/size, instead of cut.
What is the best cut grade for engagement rings?
At Harper Tait, we recommend Excellent or Very Good cut grades for engagement rings to ensure the diamond looks as beautiful as possible. In fact, these are the only cut grades we offer in our jewellery.
What is the difference between diamond cut and shape?
Cut refers to how well a diamond’s facets are proportioned, polished, and symmetrical, while shape refers to the overall outline, such as round, princess, or pear.
How can I tell if a diamond is cut well?
Side by side, the difference between a beautifully and badly cut diamond will be obvious. A poorly cut stone will not have the same life you would expect from a diamond. However, we’d suggest - if you can - coming to view some diamonds in person, where we can talk you through what to expect and look for in a stone. Please feel free to visit us and our beautiful Hatton Garden diamonds!
If you are buying a diamond without seeing it, such as online, be sure to choose an Excellent or Very Good cut. If you choose one of these grades, you won’t be disappointed.
Download our guide to diamond cuts here for further information.
