Diamond Grading – The Four C’s of Diamonds

Someone selecting a diamond with tweezers from a tray of diamonds

What makes a good diamond?

A diamond is measured on its quality and rarity.

The better the quality, the rarer the diamond and therefore the more sought after and valuable it is.

To help with consistency, the Gemological Institute of America (the GIA) devised a diamond grading system that would be universally recognised.

With clear guidelines, this ensured that you can accurately rely on the grading demonstrating the quality of the stone.

Jewellers all over the world will use this grading system and recognise the terms used.

The Four C's

There are four significant factors in grading diamonds to determine its quality (or lack of) which are known as the Four C’s.  

These four factors consist of:

  1. The Cut of a Diamond
  2. The Colour of a Diamond
  3. The Clarity of a Diamond
  4. The Carat of a Diamond

We will talk about each in turn, below. 

Man grading a diamond through a jewellers eye loupe

But what, exactly, are the Four C’s or these four key areas? 

Each of these four factors works together to influence the grading and desirability of any precious gemstone but in particular for this most precious of gemstones and the birthstone for April, the Diamond.

One of the four is not more important than the other, although a better cut may outweigh the other factors in enhancing the beauty of a diamond.

In this blog, we are going to look at these factors, known as the Four C’s.


1. The Cut

The cut, as well as the shape, of a diamond influence how much light can pass through the gemstone. It also demonstrates how much light is reflected back out of the top surface, known as the crown.

The shape of a diamond is a separate thing from the cut, although the shape often has a particular number of facets.

The shape is the outer form and shape of a diamond. The cut refers to the angles and facets cut into the diamond to best angle, reflect and refract the light to increase brilliance and fire. 

When cut well, a diamond can refract the light very successfully.

The idea is for the light to enter the diamond and pass through before being directed back out of the crown.

If, after diamond cutting, the diamond is too shallow or too deep the light will pass into the gemstone and be directed out of the base (called the Pavilion) or the side. 

Therefore, the cut of a diamond is a critical factor in enhancing the stone’s brilliance and fire.

In fact, the cut is probably the most important part of giving the gemstone its sparkling qualities.

Diagram demonstrating the way light is reflected through different cuts of diamonds
Diagram of gemstones with pattern of facets cut into the stone

Diamond Cutters have studied the art and craft of cutting diamonds to get maximum light into and directed out of the diamond in such a way that enhances the beauty of the stone.

First and foremost the cut needs to display symmetry and pleasing angles and proportions to the eye. It will also give the gemstone sparkle and ‘fire’ – in other words, it allows the stone to dazzle.

The gem cutter will want to retain as much as the carat weight of the diamond and provide the best visual appearance and brilliance to the stone.

The rough diamond will have inclusions which an expert cut will with remove or minimise.  A diamond cutter will study the rough diamond carefully to ascertain the best way to divide and cut the stone to get the best gemstones from it. 

As you can see getting the perfect cut to a diamond is a delicate balancing act in making the most of the stones best qualities, hiding or removing imperfections. 

A certified diamond is judged on the cut being able to display six qualities to the best ability.  The six qualities which is important to achieve in the cut are:

  • Brightness
  • Fire
  • Scintillation
  • Weight
  • Durability
  • Polish
  • Symmetry

The most popular shape for a diamond used in jewellery is the brilliant round diamond.  There are other shapes, such as pear-shape, marquise and oval and these are known as fancy-cut diamonds.

The cut of the diamond in the Four C’s refers less to the shape of the stone, but more to the facets cut into the gemstone.

This is what will bring about the qualities talked about in this section.

Diamonds cut into different shaped stones

2. The Colour

A perfect diamond will be colourless. Indeed the better diamonds are indicated by their degree of lack of colour.

The colour has a big impact on the price of a diamond.

The difference in colours can even be noticeable to the naked eye. 

The GIA grades the colour of diamonds against a stone of a known colour in strictly similar lighting and conditions.

All white diamonds are graded on their colour on a scale range from D-Z, with a colourless, perfect, diamond graded D.

Diagrame demonstrating different colours of diamonds and their grading
The Grading of Diamonds on their Colour

Colourless Diamonds are classed as being grades D, E and F.

Near Colourless are G, H, I, J and K.

Noticeable Coloured diamonds are those graded L, M, N.

The poorest colours (being more yellow or brown) are graded between letters S-Z 

Most diamonds in a jewellery shop will usually range between colourless to nearly colourless.

Be careful not to confuse the grading of white diamonds with coloured diamonds such as pink, black or blue diamonds which are prized and highly valued gemstones in their own right because they are so unusual.

3. The Clarity

Almost all stones have inclusions, or blemishes, within them.  Some of these inclusions are not visible to the naked eye.

A flawless diamond is incredibly rare with even most jewellers have never seen one.

Even diamonds which have few, if any, inclusions are very rare and sought-after and therefore are extremely valuable. 

The grading on the Clarity of a gemstone reflects how many inclusions it has.

There are 11 grades in the Clarity of a diamond – with most diamonds being certified falling into the VS range (Very Slightly Included).

The Clarity grading uses letters with FL being the best (and most rare, therefore the most sought after and valuable) to Included. 

The grading is as follows:

  • FL – Flawless
  • IF – Internally Flawless
  • VVS1 – Very, Very Slightly Included 1
  • VVS2 – Very, Very Slightly Included 2
  • VS1 Very Slightly Included 1
  • VS2 – Very Slightly Included 2
  • SI1 – Slightly Included 1
  • SI2 – Slightly Included 2
  • I1 – Inclusions 1
  • I2 – Inclusions 2
  • I3 – Inclusions 3

The idea of having as few inclusions as possible is that it will not interfere with or impede the light passing through the gemstone.

Diagram showing the grading of diamonds on Clarity
Diamond Grading based on Clarity

4. The Carat

The Carat refers to the weight of the diamond, measured in the metric form of a carat.

The Carat got its name from the carob seed. Early gem traders noticed that a carob seed seemed to have a reasonably stable weight. So they used carob seeds as counterweights when weighing their gemstones.

A one Carat diamond will weigh 200 milligrams (0.2 grammes). Therefore 1 carat = 0.2 grammes.

A 1-carat diamond is also equivalent to 100 points. The Gemological Institute of America has a fantastic analogy of the single Carat is divided into 100 points, just like British Pound (or a US Dollar) divided into 100 pennies (or cents). 

Therefore a ¼ carat diamond is the same as a 25 point diamond.

Diamonds of the same weight can be cut in different ways and will be a different size.

The size of of a diamond should not be confused with the Carat- remember the Carat is the weight not the size.

Indeed the size would be one of the least important factors to consider when grading diamonds. A smaller weight diamond but with a better cut will be more desirable than a larger diamond with a poor cut.

A customer recently looked at a .58 carat H VVSI1 Princess-cut diamond ring with us (that is a H Colour and ‘Very, Very Slightly Included 1’ Clarity) . But she had set her sights on a 0.7 carat ring, which we didn’t have in stock at the time. Encouraged by us, that weekend she went window shopping and saw a .7 carat ring (the size she desired) in another jewellers. She returned the following week saying that the colour of the other, larger diamond ring, even in the jewellers window, was noticeably yellow, and nowhere near as beautiful as the one she tried with us. She promptly purchased the better, but slightly smaller, diamond with us and is still delighted with it.

We mention this story to highlight the difference in the beauty of a very slightly smaller stone but with better colour and Clarity. It will always be rarer, more valuable and sought after as well as looking more beautiful.

Which is the most important in the Four C's?

Which of the Four C’s are the most important to go for?

Each of the 4C’s work together but the brilliance (ie the cut) and the appearance (in the colour and Clarity) will far outweigh the carat weight. A smaller but well-cut stone near-colourless diamond with fewer inclusions will look far nicer on the eye and be much more sparkly than a much larger but dull, yellow-tinged diamond.

Evaluating a Diamond Yourself

In evaluating a diamond yourself, there are a few things to look for, having read the information in this blog it should give you a good idea of what to look for overall. 

Overall Appearance

Look at the overall appearance of the cut – is it symmetrical?

Does the diamond sparkle?

As you turn the diamond does it flash and have ‘fire’?

Look at the colour

You will notice if the colour looks dull or slightly (even noticeably) yellow.

Check the Clarity

Check if the diamond looks clean and unmarked.  You can always ask to borrow the jewellers loupe to look at the diamond through the eye-piece.  

Does The Size of the Stone Suit Your Hand?

Does the size suit your finger and hand?  An often overlooked factor is that going up in carat weight means that a bigger stone will also sit higher on your finger, which can not only be impractical but may not suit your hand at all. 


Diamond Grading Report

Many diamonds in diamond-set jewellery you see in a jewellers will not carry a certificate. These gemstones are perfectly good diamonds,  however, the best quality diamonds are certified to show precisely where on the scale in each of the four key areas – Cut, Clarity, Colour and Carat – they sit. 

A Diamond Grading Report details the Four C’s of the diamond you are looking at, as well as detailing the country of origin of where the diamond came from.

The Diamonds we Sell

The Raphael collection of diamond rings we sell in our store and online all come in a minimum standard of F/G Colour and VS Clarity.

Each ring style, or other jewellery, is available with a choice of diamonds with regards the clarity and colour. 

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