The 4 C's - Evaluating Diamond Quality

diamon quality

In simple terms, in order to establish the value and grading of diamonds, you need to understand what is known as the 4 C's, which is Colour, Clarity, Cut, and Carat. 

This remains the universal language that was first introduced by the Gemological Institute of America, known as the GIA, and then launched by De-Beers. Working on all of the 4 C's then determines the rarity and value of a diamond, and rather like a human fingerprint, each diamond has its own individual characteristics.

There are several important factors to observe before you decide your best options when buying diamonds. As a common rule, the higher the quality of a diamond of carat weight, then the higher its actual price.

In assessing the 4 C's, you can see why it's important to understand the role they play when purchasing diamonds.


The 'cut' is fundamentally the most important feature of diamond quality as it impacts the beauty of the diamond. It refers to the proportion, facets, brilliance, fire and scintillation within the finishing details. In simple terms, let's look at each of the Cut categories:

  • Facets: These are the flat surfaces on the geometric shape of the diamond, which can have as many as 58 facets.
  • Brilliance: The amount of internal and external white light transmitted from an individual diamond.
  • Fire: Denotes the amount of light transmitted like the vibrant colours of the rainbow.
  • Scintillation: The quantity of sparkle and reflection the diamond produces.

The GIA grades diamonds as the following: Ideal, Excellent, Very good, Good, Fair and Poor.

How light reflects through a diamond

Cuts vary extensively among diamond cutters, even if two diamonds are given the same grading on a cut chart. Sometimes a cutter may aim for the maximum carat weight and leave the diamond too shallow for maximum light reflection. Alternatively, a diamond may be cut to minimise the number of inclusions and improve the clarity, but forgoing the maximum sparkle. However, it's essential to ensure that Cut is the main aspect of your diamond selection as it's the most significant factor in the beauty of the diamond. 


The GIA grades all diamonds from D to Z, with D being the least colourless and Z containing traces of brown or yellow tints. 

Generally, a completely colourless diamond will command the highest price, whereas the ones that are graded D are the rarest, most expensive, but also have the best colour.

  • D-F Colour Diamonds are near-colourless in appearance, with no apparent colour, and are of excellent value for the quality.
  • G-J Colour Diamonds offer a tint of colour diamonds. These are inexpensive and go well with yellow gold.
  • K Colour Diamonds have a definitive colour. 

It is important to remember that different diamond shapes reflect colour at varying strengths, so your choice of most favourable colour, balancing the diamond's appearance and diamond's price, will depend greatly on what particular diamond shape you've chosen.  

Essentially the most decisive aspect with colour is whether it appears colourless with regard to the setting, as you need to establish whether there's any hint of colour that may detract from white and coloured light reflections. It's interesting to note that certain coloured diamonds are very valuable stones, such as a pink or a green diamond. A diamond colour chart varies enormously, and the exact colour you choose will depend on your budget.

Did you know?

Red diamonds are the rarest of coloured diamonds, with only 20-30 existing in the entire world! They get their magnificent red colour from an extremely rare process obtained during their formation, which changes the crystal make-up of the diamond and in turn allows light to pass through it differently from colourless diamonds.

Also extremely rare, most green diamonds get their colour from natural radiation in the rocks around them. Usually, only the outside or surface area of the diamond is green, with the colour rarely making it to the centre of the diamond. 

Let's not forget a mention of the magnificent 59.60-carat Pink Star diamond worth around $1.2 million per carat, the diamond was mined by De Beers in 1999 in South Africa, and weighed 132.5 carat in the rough. The incredible Pink Star is the largest known diamond, having been rated Vivid Pink.


The GIA follows the diamond clarity chart set out below.

  • 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)

Interestingly, no diamond is absolutely pure, but the better it is for absolute purity, the better the overall clarity of the stone. 

Many imperfections are invisible to the naked eye, and only experts can clarify the exact quality and clarity. Clarity will affect how the diamond sparkles and attracts the light, and fewer inclusions mean the diamond will shine and sparkle more brightly under the light, remembering, of course, that no two diamonds are exactly alike. 

'Eye-clean' is an expression used in the industry to describe the clarity of a diamond that is visibly clear to the naked eye. This is an important consideration when it comes to purchasing a diamond. So many diamonds sold online disappoint, so it's vital to understand the diamond clarity chart.

SI2 diamonds tend to have more imperfections and more obvious inclusions than superior grades, such as the SI1 and VS2, but every so often, you can find an 'eye-clean' stone. If you can find an 'eye-clean' SI2 diamond, you'll most certainly get the maximum for your budget.  

An 'eye-clean' diamond offers excellent value, being much less expensive than flawless (FL) or internally flawless (IF) diamonds, which are extremely rare and therefore command a higher price.

To avoid confusion by wondering which the best clarity is, it's interesting to note the most accepted clarity today. The most popular diamond clarity grade in the marketplace is VS1, closely followed by VVS2. These diamond clarity grades offer the greatest value because they cost less than the rare grades, such as flawless and internally flawless, but still offer an eye-clean appearance.

Also, bear in mind that clarity characteristics are much harder to detect within small diamonds. However, a large diamond weighing 2 carats, 3 carats, or 4 carats with SI1 clarity characteristics will, of course, show inclusions more easily owing to the large table size. 

Evaluating Diamond Quality

Carat Weight

This is often mistakenly confused with the actual size of the diamond when in fact, it refers to the weight of the diamond. For example, an A1 carat diamond equals 200 milligrams, or 0.2 grams, and weighs around the same as a quarter of a raisin. Also, depending on the shape of the diamond and the Cut, then two 1 carat diamonds may be totally different in size. 

Comparison in round cut diamond

Essentially everyone wants to purchase and own an outstanding diamond, both in setting and brilliance, but equally, you need to examine the carat, depending on your budget. As an example, a 1.5-carat diamond will not shine as brightly as a stunning sparkling 1.0-carat diamond, irrespective of its weight. Therefore, it's advisable to choose a diamond with an excellent cut or an ideal cut in the shape and design of your choice. 

Which is the most important of the four C’s?

  • Cut:  This remains the most important of all the diamond characteristics as it most readily conveys a diamond's beauty. Look for high levels of brilliance and fire, and perhaps reduce your budget in other areas like clarity or colour to ensure an exceptional Cut.
  • Colour:  The most probable essential aspect to focus on is colour. A diamond should appear white or colourless to the naked eye. Make sure the colour does not distract or obstruct with any white and coloured light reflection.
  • Clarity:  Again, this is an important characteristic to consider. Most certainly choose a diamond that is 'eye clean'. Blemishes and any inclusions should not divert from the brilliance, sparkle or fire of a diamond.
  • Carat:  Last but not least. It's always down to budget but take time to consider what is important for you. If you're choosing a diamond in an engagement ring and impressing your love, that's fine, but remember that brilliance and beauty will outshine the weight each and every time. Consider lowering your carat weight to ensure you purchase a stunning glittering diamond.

So, remember, a diamond is forever, as the slogan goes, so it's imperative to get things right at the onset. Diamonds will always hold their value and are a sign of never-ending love and remain a treasured possession to this day. 

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