Discover how cut can transform the beauty of a diamond and impact its price and desirability.
What’s in a cut? It’s an aspect of diamond buying that you may not have spent an awful lot of time thinking about. Often buyers fixate on their dream number of carats or perhaps the shape of the precious stone they are searching for.
Cut can quickly become an afterthought. It shouldn’t be. Cut is the single most important factor in releasing the beauty and sparkle of a diamond. Even the most impressive natural stone will appear dull and murky with a poorly executed cut.
Understanding how a great cut transforms a stone, and enhances its natural brilliance and fire, can help you select a diamond that truly dazzles. Explore our expert guide to diamond cuts and improve your diamond knowledge, below.
What is Diamond Cut?
It’s sensible to start with just what we mean when we talk about the cut of a diamond. Cut refers to the proportions, angles, and overall symmetry of a stone.
It is these minute differences in angles and proportions that impact how a diamond interacts with light, determining its brilliance and sparkle. What, on paper, is essentially maths, is the number one determining factor in your diamond’s beauty.
A well-cut diamond will attract much greater prices than a poorly-cut one. And you should never buy a diamond without carefully examining the cut or receiving expert advice.
When we look at a diamond to review the quality of its cut we are looking at a range of factors, including:
• Proportions - These include the table, width, and depth of a stone.
• Symmetrical Facets – This includes the mirrors, windows, and steps of a diamond.
• Fire – How a diamond disperses coloured light.
• Scintillation – The sparkling flashes a diamond reflects as it moves through light.
• Brilliance – The reflection of white light by a stone.
• Finishing Details – Any final treatments or polishing processes a diamond has undergone.
What is The Difference Between Diamond Cut and Shape?
Diamond cut and shape are often confused as one and the same. So, before we dive deeper into cut, it’s useful to outline the different meanings of these words when applied to diamonds.
Shape is used to refer to the overall outline of a diamond, for example, pear or heart-shaped. Cut refers to the dimensions, symmetry, and reflective qualities of a stone. Cut and shape are sometimes used interchangeably, but you should keep these distinct meanings in mind.
To learn more about diamond shape, read our article Diamond Shape: The Ultimate Guide.
Understanding the Proportions of a Diamond
The proportions of a diamond are determined by its table, width, and depth. We take a closer look at each of these factors, below.
A diamond’s table percentage is calculated by dividing the width of the top surface area (or table) by the width of the diamond. For example, if the width of the table is 2.5mm, and the width of the diamond is 5mm, the table percentage would be 50%.
The ideal table percentages can vary depending on the shape of the diamond, so it’s useful to get an expert opinion on the ideal percentage range for the shape you are searching for.
Too large a table percentage and light won’t properly reflect from a diamond’s facets, too small and the light will be absorbed and fail to be properly reflected towards the eye.
A diamond’s width is measured across its widest point. This measurement is important for determining how proportionate a diamond is in reference to its shape and calculating its table percentage.
The length to width ratio is calculated by dividing a stone's length by its width. So, if you have a diamond with a length of 6mm and a width of 4mm, its ratio is 1.5.
Desired ratios vary depending on the shape of the diamond under review, and you should consult a jeweller for the ideal ratio bracket for the type of diamond you are looking for.
Depth measures the height of a diamond from its base (culet) to the top of the table. Diamond depth can be measured in millimetres or as a percentage calculation (depth divided by width).
A shallow diamond may appear larger, which can be useful for making a smaller weight of stone go further. However, a shallow depth may also inhibit reflection of light and make a diamond shine less brightly.
Why do Diamond Proportions Matter?
The proportions of a diamond are the most important factor in the way a stone reflects the light. Poorly planned and executed proportions in a diamond cut can make a stone appear less brilliant and scintillating.
Finding the right proportions for a diamond is a case of carefully balancing angles, facets, and ratios. These complex calculations need to be carried out by a diamond expert, as even a slight error can significantly impact the overall look of a diamond.
What is The Best Diamond Cut?
There is no one single cut or set of proportions that is the ‘best’ for all stones and shapes. Essentially a well-cut diamond is one that effectively reflects light back towards the eye, rather than absorbing light that then leaks out of other parts of the stone.
The GIA (Gemological Institute of America) describes the highest possible grade of cut as ‘excellent’. While the AGS (American Gem Society) call it ‘ideal’. These terms are used to describe a well-proportioned diamond that provides optimal reflection of light.
‘Excellent’ cuts are highly sought after and valuable. We would always recommend choosing cut over carat size when picking a diamond, as cut has such a significant impact on the beauty of a stone.
Shallow and Deep Diamond Cuts
One of the biggest factors that can affect the beauty of a diamond is how shallow or deep the cut is. A shallow cut means that light hits the stone at a low angle, often travelling through the stone rather than reflecting back towards the eye.
On the other hand, a cut that is too deep creates sharp angles. These can cause light to reflect back onto another part of the diamond and, again, pass through the stone and away from the eye. The perfect depth of diamond cut lies somewhere in-between these two extremes.
Grading and Certification of Diamond Cuts
The Gemological Institute of America or GIA is one of the world’s leading authorities on diamonds, using well-defined scales and measures to grade diamonds from around the world.
A non-profit organisation, the GIA provides independent, expert diamond advice and certification. Their scale for diamond cut is rated from excellent and very good through to fair or even poor:
Excellent cut diamonds have the highest level of fire and brilliance. Almost all of the light is reflected through the table, allowing the diamond to radiate with outstanding sparkle.
Very Good cut diamonds have exceptional brilliance and fire. A large majority of the light reflects through the diamond’s table. To the naked eye, Very Good diamonds offer similar sparkle to those with an Excellent grade.
Good cut diamonds display brilliance and sparkle, with a lot of the light reflecting through the table to the viewer's eye. These diamonds offer beauty at a lower price point. They really are special and provide sparkle and love for of the light reflects through the table to the viewer’s eye. These diamonds offer beauty at a lower price point.
Fair cut diamonds deliver little brilliance, as light can easily escape through the bottom and sides of the stone. Diamonds with a Fair Cut may be a satisfactory choice for smaller carats and to use as side stones.
Poor cut diamonds yield practically no sparkle, brilliance or fire - light escapes from the bottom and sides of the diamond.
You should always ask whether a diamond is certified before you buy and enquire about its cut grading. However, there are many reasons a diamond may not be certified and an expert opinion on the quality of diamond cut should also be sought from a trusted jeweller.
We wouldn’t recommend investing in a diamond with a cut grade less than very good. The stone will simply never sparkle in the way you expect, and you may be disappointed.
How is Diamond Cut Quality Assessed?
Assessing a diamond cut is complex and it takes years of expertise to be able to fully appreciate and understand the cut of a beautiful stone.
Jewellers and diamond experts will evaluate proportions, symmetry, and overall polish in their assessment of a stone, carefully looking at it under a bright lamp and daylight to understand how well it reflects light.
However, you can begin to understand the quality of cut, by observing how a diamond behaves under the light, looking for dark spots within the stone, and assessing any signs of dullness and flatness.
Make sure you examine a diamond carefully and don’t rush into a buying decision without first examining a stone under both natural and artificial light. A good jeweller will provide their expert opinion on diamond cut before you buy, allowing you to better understand the stone you are considering.
How Does Cut Quality Affect Price?
The short answer is greatly. Cut has everything to do with a diamond’s ability to sparkle, and without that magical brilliance and fire, it simply isn’t very desirable.
An excellent cut will increase the value of a diamond more significantly than any of the other Cs and it should always be at the top of your wish list.
If you have a tight budget, we recommend investing in an excellent cut over clarity, carat, or colour. An exacting cut really is the secret to a beautiful diamond.
Looking to invest in diamond jewellery?
Our expert team at Burrells can help. Step into one of our stores today for friendly and knowledgeable support and advice on diamond buying. What’s more, we have an impressive range of stones and diamond jewellery to explore, carefully hand-picked by our Head Diamond Buyer Adam Gillary DGA.