What is diamond cut?

Diamond 'cut' is often mixed up with diamond shape which refers to the outline form of a diamond after it has been cut. Diamond cut denotes how well a diamond's proportions have been finished.

For example, how deep has the diamond been cut? How do the angles of the diamond interact and produce light? Are there any defects on the surface? etc. Although this sounds a little over the top, cut determines the overall beauty of a diamond. In other words, the better the cut, the more a diamond will sparkle!


Factors that affect diamond cut quality

Subtle differences in a diamond cut greatly impact the overall appearance and therefore cost of a diamond. As you can imagine, there are a lot of factors that can change the appearance so, to make things simple, we've grouped them into 6 of the most important:

1. Proportions

By far this is the easiest to identify with the naked eye because proportions directly affect a diamond's ability to reflect light. If it is cut well, a round shaped 'ideal' cut diamond will show no dark areas when looking down through it from the top.

What if the cut is too deep?

If looking at a deeply cut diamond there won't be any sparkle showing in the centre. This is because all the light is being lost though the lower facets and nothing is being reflected back through to the top.


What if the cut is too shallow?

When a diamond is cut too shallow, is looks darker around the outer edges of the stone due to the light being reflected by the sharply angled lower portion.


How to tell if it's ideal

An ideal cut diamond ensures all the light is captured and thrown back through the top of the diamond, meaning lots of sparkle. If you can see little to no dark areas when looking through the diamond, it is well cut to optimise its light performance.


2. Symmetry

Symmetry measures how precisely the facets of a diamond are aligned. If they are misaligned it can cause light to be reflected in a different way or sometimes not at all. Sometimes when symmetry is slightly off, it can be done on purpose to cut out an imperfection. The job of a diamond cutter is to get the best out of a diamond, if it has defects which will appear more unsightly than slight lack of symmetry, then this is often a compromise.


3. Brightness

Sometimes referred to as 'brilliance', brightness is the amount of white light a diamond reflects back through the stone; the less light leakage, the better the brightness.


4. Fire

Fire refers to the 'dispersion' of light that often looks like flashes of the colours of the rainbow. A well cut diamond displays a lot of fire when the diamond is seen in low light.


5. Scintillation

Often referred to as the 'life of a diamond', scintillation is the flashes of light that are visible when the diamond is in motion. In other words, scintillation is a diamonds sparkle and the pattern of that sparkle.


6. Polish

Polish is the measurement of the smoothness of a diamond's facets. When a diamond is polished it can create surface defects which can disrupt 'light performance' and interfere with brightness, fire & scintillation.


Diamond cut scale - How cut is measured

Like the other aspects of a diamond, the cut is graded on a sliding scale from poor to excellent. An excellent cut diamond means that the proportions of the diamond are extremely well cut and other quality factors are optimal to produce maximum sparkle.

For example, even with a high colour and clarity grade, if the cut of a diamond is poor then the diamond won't have the same brightness of a well cut diamond. As long as a diamond has a good/ very good or excellent cut grade it will create a good level of sparkle.


An excellent cut means there are no or very insignificant features visible on the diamond surfaces and you should struggle to see them under 10 x magnification.

Very Good

Very good cut means there may be small features which can be seen under 10 x magnification.


On a good cut diamond there are some noticeable features which are visible under 10 x magnification. The overall lustre of the diamond may be impacted.


Dropping down to a fair cur means any flaws in the cut are obvious under magnification. It will also affect the overall lustre of the diamond.


The flaws in the cutting process will be visible without the use of magnification. The lustre of the diamond will be very affected.

Why are some diamonds better cut than others?

You might be thinking at this point, if a well cut diamond holds the highest value, why would anyone cut it badly? Well, diamond cutting can be complex, and cut is just one quality factor, other factors need to be balanced depending on the size of the rough diamond and the desired outcome.

For example, a 1 carat diamond will yield a higher price than a .90 carat diamond, so a jeweller may have to compromise on the cut of a diamond by faceting the diamond differently to preserve carat weight by keeping raw material on a diamond, rather than producing a better cut but a lower carat weight.

In other words, because diamonds are so valuable and rare, diamond cutters have to calculate and plan how to get the best out of the raw material they have.


Expert Buying Tip:

We regard cut as something you should consider over anything else because we believe it is the biggest factor when it comes to overall beauty. Question your jeweller and ask them to show you the diamond loose before it has been set if possible so you can look through it from the top and bottom to check if it behaves the way you want it is appealing to your style.

Our recommendations for buying the right diamond:


  • Round brilliant cut diamonds hold the highest premium because they have always been the most popular. This has led to unique and more refined cutting techniques which makes this diamond shape hold a higher price.
  • Ask your jeweller to show you the diamond in different light situations if possible. Flaws in the cut may not be immediately obvious and can look different in varying light scenarios.
  • Fancy cut diamonds (all other shapes apart from round) don't have 'ideal proportions' when they are cut, so don't concentrate too much on the scaling and go with your gut on these diamonds.
  • Look for shadowy looking dark areas in a diamond, if there are large dark areas avoid them as generally speaking, they simply won't sparkle as they should.
  • Look for fire or 'colours of the rainbow' being reflected out the top of a diamond. This is the great sign of a well cut diamond.

Have A Question?

Contact us by phone at 0141 221 5855 or by email at [email protected]. We love our work and will be happy to help you with your query, we can also book a convenient time for a consultation to find the exactly what you need.


Simon Porter

Director, James Porter & Son

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Simon is the 5th generation Porter to look after the day to day running of the James Porter & Son store since its inception in 1858. Working alongside his father since 1995 and eventually taking over the reins full time in 2007.

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