Diamond Cut

A diamond’s cut is the single most important of the 4 C’s to evaluate before buying your engagement ring. Of course the carat size, color and clarity will each play their part in the outcome of a well rounded, quality stone. But if the cut grading is not of a high enough standard, your diamond just won’t be bright enough or sparkle like you want it to.

The 'cut' is not the shape of the stone, it actually refers to the diamond’s internal proportions, symmetry and polish.

At Kensington we stock 'Excellent' and 'Very Good' cut graded diamonds. We do not carry 'Good', 'Fair' or 'Poor' gradings as we consider the cut to be a diamond's most important attribute, and strive to only work with the brightest and best diamonds.

'Triple Excellent' (also known as '3EX') diamonds contain excellent gradings in all cut, symmetry and polish categories. They offer the very best light performance available.


Stocked by Kensington Diamonds.
Not stocked by Kensington Diamonds.



This is the relationship between the size, shape and angle of each facet of a diamond. A brilliant round diamond has fifty seven facets, if all facets are proportioned correctly at the right angle, when light shines into the diamond a maximized amount of light will reflect back to the eye.

This reflected light takes on three attributes: Brilliance, scintillation and fire. A diamond with an ‘Excellent’ cut grading is proportionally so well-balanced, it will display a perfect amount of each:

The Diamond’s ‘Brilliance' The sum total of radiant flashes of bright white light, reflected back into the eye from the top of the diamond.
The Diamond’s ‘Scintillation’ What people would describe as the diamond’s ‘sparkle’, intense flashes of black and white as you move the stone.
The Diamond’s ‘Fire’ Rainbow like flashes of vivid color, caused by the dispersion of light as it travels through the diamond.

If a diamond is cut too shallow then its diameter from the top down will appear wider, giving the impression a one carat for example may in fact be a larger stone. However due to its top heavy nature, light will enter in through the top, strike the diamond’s pavilion facet at a low angle and lose the vast majority of its light reflection out of the bottom. This results in a lack of brilliance and a lifeless sparkle.

Similarly, a diamond cut too deep will lose the majority of its light refraction out of the sides of the stone, creating a duller, darker appearance.


We strongly advise that customers treat the cut grading as the most important characteristic of the 4 Cs when purchasing a diamond. If you want a diamond that sparkles and looks alive, we would recommend buying ‘Excellent’ - this grade maximises brilliance and fire, offering exceptional light reflection back to the eye. ‘Very Good’ still offers great light performance at a lower price-point, but we would recommend not to consider any grade lower than this.

It would make more sense to sacrifice a grading of color or clarity, than it would to make any concessions on the cut grading.

EXCELLENT CUT Maximum brilliance and fire, will reflect almost all of the entering light, creating an exceptionally bright diamond full of life.
VERY GOOD CUT A superior brilliance and fire, will reflect the majority of entering light. An attractive option at a lower price point.
GOOD CUT Reflects a substantial amount of the light for an average appearance, however noticeably duller than its better ranked counterparts. We do not stock any diamonds below a 'Very Good’ cut grading.


A diamond’s ‘Symmetry’ grading measures how precisely the facets align and are symmetrical to one another on both sides. If there are even tiny mis-measurements then light will be reflected between facets at an incorrect angle, leading to a lessened brilliance when looking down at the diamond.

Once again, if you are looking for maximum light reflection from your diamond then we would recommend you select an excellent grade of symmetry. Very good still offers good light performance at a lower price-point, but we would recommend not to consider any grade lower than this.

EXCELLENT SYMMETRY No symmetry defects visible, even at 10x magnification.
VERY GOOD SYMMETRY Any defects are difficult to see, even under a microscopic lens at 10x magnification. An attractive option at a lower price point.
GOOD SYMMETRY Defects may still be difficult to see under 10x magnification, however in order to ensure no sacrifice is made to the brilliance, scintillation or fire of our diamonds - Kensington Diamonds do not hold any stock rated below a very good symmetry grading.


The 'Polish' grading measures how smoothly the outside of a facet has been polished.

Diamond producers take a great deal of care to ensure a diamond is polished to the highest standard possible, after investing so much time and effort into crafting it from a rough stone into an outstandingly cut piece of jewellery.

However varying standards still exist: An excellent grading will show no visible defects at all under 10x magnification. A very good grading may mean tiny defects such as nicks, scratches or burns could show up, but only after a trained expert has spent a while looking at it through a magnified lens. These are impossible to see with the naked eye.

Dropping down to a good grading would mean polishing defects are more numerous and easier to see under 10x magnification, but still almost always remain invisible to the naked eye.

So to conclude the polish grading doesn’t bear as much importance as the cut and symmetry of a diamond, however we still recommend to choose an excellent or very good grade where possible.

EXCELLENT POLISH No polish defects visible at 10x magnification.
VERY GOOD POLISH Any defects are extremely difficult to see at 10x magnification.
GOOD POLISH Any defects are difficult to see at 10x magnification. Kensington Diamonds do not hold any stock rated below very good polish grading.


When all three of the cut, symmetry and polish categories are graded excellent from the GIA (Gemological Institute of America) - a diamond is labelled a ‘Triple Excellent’ or ‘3EX’. These diamonds offer the top level of cut quality and outstanding light performance available.

(Example GIA grading certificate on a triple excellent diamond):
At Kensington Diamonds we can help you to source from a wide variety of triple excellent graded diamonds here.


Examining the cut grading of a round diamond is very straightforward, as the GIA outlines the cut parameters of their internal proportions.

For fancy shapes however (anything non-round, such as princess, oval, cushion, radiant, asscher, heart or pear diamonds) there is no standard cut grading, because there are simply too many variables to calculate within these different shapes.

Therefore it is important to instead look at the inner angles and proportions, to make sure you are getting a beautiful, sparkling diamond.

If you are considering a fancy shape instead of a round it is better to speak with an expert. Get in touch and we will show you exactly what you should be looking for.