What Makes A 'Good' Diamond?: The 4 C's of Diamond Quality Skip to content
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What Makes A 'Good' Diamond?: The 4 C's of Diamond Quality

Shopping for a diamond ring can be quite daunting. We all know a large part of a diamond's appeal is their fiery brilliance, but without the proper knowledge, it can be difficult to accurately pinpoint which exact characteristics can be used to tell a high quality from a diamond of poorer quality. Before the arrival of the 4Cs, which is a grading system developed by the Gemological Institute of America (GIA) in the 1950s, even diamond experts struggled to agree on how to classify diamonds. 

What are the 4c's?

The 4Cs are Carat Weight, Colour, Clarity and Cut. The GIA determined that these were the four most important factors that diamond experts and consumers should pay attention to when examining a diamond. The GIA also developed sub-scales to grade each 'C' - but we'll get more into this in just a moment.

This grading system made it easier to compare one diamond to another, a difficult achievement considering every diamond is unique, and for that reason the 4Cs are now the industry's most widely accepted method of diamond grading all around the world, commonly used amongst jewellers and shoppers alike.

So now that you know that a diamond's quality depends on it's carat weight, colour, clarity and cut, let's look into how each of these factors affect the overall appearance of the diamond, and the sub-scales that are used.

Carat Weight 

Carats are the most widely recognised of the 4Cs. A popular misconception is that carat weight is the most important, or even the only factor to consider when selecting a diamond. While some may prefer a heavier carat weight, it's crucial to consider the cut, colour and clarity in order to avoid disappointment.

Carats simply measure the weight of a diamond, with one metric carat being equal to 200 milligrams, or about the weight of a small paperclip. You'll often see carats abbreviated to 'ct.' 

It's important to also remember that a higher carat weight doesn't always mean a larger diamond, as diamond size can vary depending on the shape.

For example, a 1 carat pear cut diamond may be larger in terms of size when compared to a 1 carat round-brilliant cut diamond, purely because the pear shaped diamond is longer in length. 

The carat weight of a diamond, combined with the remaining 4Cs, have a direct impact on the diamond's value. Put simple, larger diamonds are rarer and therefore worth more. 
 The carat weight of a round brilliant diamond and its approximate size in millimetres. 


When looking at a diamond's colour, we're actually looking for a lack of colour. The more colourless a diamond is, the more valuable it is. This is because colourless or clear diamonds allow the most refraction of light through the stone, resulting in optimal sparkle and brilliance, which is one of a diamond's most desirable qualities.  
Due to the way natural diamonds are formed within the earth, many diamonds have a slight yellow tint, making colourless or near-colourless diamonds quite rare. 
Many of these colour distinctions are so subtle that they are undetectable to the untrained eye, but can have a huge impact on the price of a diamond.
Diamond colour is graded on a scale from D to Z, with D being colourless and Z being the worst colour quality.


Diamonds have tiny internal flaws called inclusions, which form within the stone while the diamond is being created. Diamonds can also have external flaws as a result of scratches on the diamond's surface - these external flaws are called blemishes.
The size, position and visibility of these flaws can have a significant impact on diamond clarity.
Diamond clarity is measured using a scale that grades the diamond based on the presence (or absence) of inclusions and blemishes, as well as their size, position and visibility under 10x magnification. A diamond with absolutely no inclusions or flaws is referred to as 'flawless,' abbreviated as 'FL.' Flawless diamonds are extremely rare and carry a very high price tag as a result.
It's important to note that inclusions are microscopic and typically only visible under 10x magnification, which means that a diamond does not have to be graded as 'flawless' to be 'eye clean.' When a diamond is 'eye clean,' it has no imperfections that are visible to the naked eye, which means you will not be able to notice the inclusions in an eye clean diamond unless you ask a qualified jeweller to examine the stone on your behalf. 
On the clarity grading scale, eye clean diamonds are classed as:
  • Flawless (FL)
  • Internally Flawless (IF)
  • Very Very Slightly Included 1 (VVS1)
  • Very Very Slightly Included 2 (VVS2)
  • Very Slightly Included 1 (VS1)
  • Very Slightly Included 2 (VS2)

At the lower end of the clarity scale, we have diamonds that have multiple inclusions and external flaws, which may visibly affect the way the diamond reflects light and as a result, affect the diamond's sparkle. These diamonds are classed as: 

  • Slightly Included 1 (SI1)
  • Slightly Included 2 (S12)
  • Slightly Included 3 (S13)
  • Included 1 (I1)
  • Included 2 (I2)
  • Included 3 (I3)



A diamond's cut quality depends on how well light passes through the diamond, which determines the diamond's brilliance. Diamond enthusiasts have been researching and developing new methods of diamond cutting for as long as diamonds have been worn as jewellery. The radiant cut, developed by Henry Grossbard in 1976, is an excellent example of diamond cut innovation. The radiant cut was developed with the intention of combining the fire and excellence of the popular round brilliant cut with the elegant shape of the emerald cut. 

A well-cut diamond is well-proportioned, symmetrical and well polished, allowing light to enter and reflect out of the stone for optimal brightness and scintillation. A well-cut diamond will appear sparkly and bright, while a poorly cut diamond will appear dull and lack-lustre. 

As a result, a larger diamond with a higher colour score that is poorly cut can potentially be less valuable than a smaller diamond with a lower colour score that is well-cut.

From left to right: diamonds with excellent, good and poor cut


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