The 4 C’s – The Complete Guide to Diamond Quality

If you are looking to buy a Diamond or just looking to learn more about these amazing gemstones, then you will no doubt have seen or heard the 4 C’s being mentioned but what do these mean?

Well, that is what I’m going to cover in this post as I will cover each of these 4 quality factors in detail and a couple of other quality factors that you need to know about.

But who am I? My name is Paul Haywood FGA DGA, I’m a qualified Gemmologist and Diamond Grader through the Gemmological Association of Great Britain and have taught Diamond Grading in the past, so I do know a thing or two about Diamonds, so let;s get started…

What Are The 4 C’s of Diamonds?

The 4 C’s stand for Color, Clarity, Cut and Carat and are the four main quality factors by which a Diamonds quality is assessed.

These quality factors also play a big part in a Diamond’s price as they better the quality of the Diamond, the more it is worth.

The 4 C’s – Color

The first of the 4 C’s is color and when we are talking about color in Diamond, there are two main categories:

1: Colorless Diamonds

Around 98% of all Natural Diamonds fall into the ‘colorless’ category (even though only a small percentage are actually colorless) and these are Diamonds that have either no color or a small tint of color, which is usually yellow or brown but can sometimes be grey.

And when we talk about colorless Diamonds, we are talking about how free from color the Diamond is and the less color in the Diamond, the higher the color grade.

The color grading chart that was developed by the GIA in the 1950s is by far the most commonly used within the industry and the colors range from D (colorless) to Z (light tint).

But what most people don’t know is that a Diamond’s color is graded by looking through the pavilion of the Diamond and not through the top as this gives a true representation of the color of the stone.

If you are looking to buy a Diamond, there is lots of ‘information’ out there about color that isn’t completely correct but some information that might be helpful is:

  • D, E & F Color Diamonds are completely colorless and the difference comes down to how bright they are, so a D color will be brighter than an F color
  • G Color Diamonds are also colorless (even though GIA say near colorless), they just aren’t as bright as D – F color
  • H Color Diamonds are colorless when viewed through the top of the stone, as you would see it in a setting and only a very faint hint of color can be seen in the pavilion
  • I Color Diamonds is the first grade where any hint of color can be seen through the top of the stone
  • M – Z Color Diamonds are often referred to as Tinted Diamonds and are actually quite difficult to buy

If you are looking to buy a colorless Diamond, then I would avoid I – M color stones and go for a F, G or H as they are colorless and if they are cut well, look absolutely amazing.

For the majority of buyers, the visual difference between a D/E and F/G/H isn’t going to be noticeable, especially when the Diamond is set and as D/E color stones attract a premium, it comes down to personal choice and budget as to whether the higher grades are worth paying for.

2: Fancy Color Diamonds

The other 2% of Diamonds are known as fancy color Diamonds and for a Diamond to fall into this category, it needs to:

  • Possess a rare color such as Red, Blue or Pink
  • For Yellows and Browns, the color must be stronger than a Z color on the grading scale mentioned above

And the method for assessing the color is different to colorless Diamonds as it is based on the:

  • Hue – which is the general appearance of the color, for example, blue or pink. There may be more than one hue present and you may see greenish blue on a report, in this case, the last color mentioned is the strongest body color seen in the diamond and the preceding colors are weaker hues that are visible
  • Tone – describes how light or dark the color is
  • Saturation – describes how strong the color seen is, from faint to vivid

It is the combination of these three factors that result in the description of color and the diagram below is how GIA grade fancy colors.

GIA Colour Grading

Ideally, when buying a fancy color diamond, you want the color to be either fancy, fancy intense or fancy vivid as these are when the stone possesses a strong, beautiful color that is not too light or dark.

There are some Faint, Very Light and Light Diamonds where it can be difficult to see the color, such as a Very Light Blue Diamond that I once looked at and if I hadn’t seen the report, I would have said it was colorless.

The 4 C’s – Clarity

The second of the 4 C’s is Clarity and the clarity of a Diamond is graded on how free the Diamond is from inclusions, with some people referring to this as how ‘clean’ the stone is.

If you aren’t sure what an inclusion is, it is basically an imperfection within the Diamond and can include things such as:

  • Crystal inclusions – this is where there is a small crystal within the stone, this can be another Diamond or other gemstones that form in similar conditions such as Garnet
  • Clouds – these are a number of small inclusions, usually very small crystals that are grouped together within the Diamond
  • Fracture – this is a non-directional breakage within the Diamond
  • Cleavage plane – this is a direction breakage within the Diamond (only found in I clarity Diamonds)

When it comes to grading the clarity of Diamond, the most commonly used grading chart is the one that was developed by the GIA and includes the following grades:

  • Flawless (F)The diamond is free from any inclusions or blemishes
  • Internally Flawless (IF) – The diamond is free from any inclusions but has a very small surface blemish
  • Very Very Slightly Included (VVS) – There are very very small inclusions within the stone that are very difficult to spot using 10x magnification
  • Very Slightly Included (VS) – Very small inclusions that are difficult to spot under 10x magnification
  • Slightly Included (SI) – The diamond has small inclusions that are easy to see under 10x magnification
  • Imperfect/Included (I) – The diamond has easily noticeable inclusions, sometimes visible to the naked eye, stone also has beauty and/or durability issues

And these grades are assigned by viewing the stone under 10x magnification, with inclusions visible through the top of the stone having a bigger impact than ones that can be seen through the pavilion.

As you can see in the image above, the VVS, VS and SI have two subcategories for each but why is this?

The official answer to this is that the size and location of the inclusions is a deciding factor but this doesn’t really explain it in my opinion and from experience, the difference a 1 and 2 is:

  • The inclusions for a 1 are generally located under the crown facets, making them more difficult to see
  • The inclusions for a 2 a generally more central and usually under the table, which makes them easier to see

For the I clarity grade, you will see that there are three subcategories but the reasons for these are different to the ones mentioned above as:

  • I1 Clarity Diamonds have inclusions that impact the beauty of the stone
  • I2 Clarity Diamonds have inclusions that notable impact the beauty or affect the durability of the stone
  • I3 Clarity Diamonds have inclusions that impact the beauty and durability of the stone

I generally recommend avoiding I Clarity Diamonds due to the looks and/or durability of the diamond being affected and instead, go for an SI1 or better.

The 4 C’s – Cut

Cut is arguably the most misunderstood of the 4 C’s as there are many people that think that Cut is the style of cut, such as Round Brilliant or Princess but what it actually is, is the quality of the cut and it is arguably the most important of the 4 C’s.

This is because the quality of the cut has a big impact on how the stone looks, with well-cut Diamonds having lots of life and sparkle and poorly cut stones looking dull and lifeless.

But what factors affect the quality of the cut, well there are three main things:

1. Proportions

Anatomy of a Diamond Cut

This is the most important of the three elements as these are basically the dimensions of the Diamond and includes:

  • Table width
  • Crown angle
  • Crown depth
  • Pavilion angle
  • Pavilion depth
  • Total depth
  • Girdle thickness
  • Culet size
  • Star facet length
  • Pavilion facet length

For each of these 10 factors, there are a range of parameters, which means that two Diamonds can have the same cut grade but different proportions and can result in the stones looking a little different.

Currently, only Round Brilliant Cut Diamonds have a set of ‘ideal’ proportions and are the only style of Diamond that is assigned a cut grade by the GIA.

2. Symmetry

The second factor is symmetry and this is broken down into two categories:

  • Proportional Symmetry – this is things like if the table is centered, the girdle is even all the way round and angles are the same on all sides
  • Facet Symmetry – this is basically do the facets on one side look the same as the other and includes things such as extra facets or facet edges not meeting properly

Basically drawing an imaginary line down the middle of the stone and seeing if one side looks the same as the other.

Some differences in proportional symmetry can affect how the stone looks as slight changes to angles etc can affect how light interacts with the Diamond.

3. Polish

This is the quality of the final polish as not all Diamonds are finished to the same standard and stones with a lower quality final polish may have:

  • Polishing lines of facet faces
  • Burn marks on the surface of the Diamond
  • Unpolished areas, either from the original crystal or earlier polishing stages

Some small polishing imperfections will only be noticeable under 10x magnification.

As I said above, currently only Round Brilliant Cut Diamonds are given a Cut grade and each of these three factors are individually graded from one of five grades:

  • Excellent
  • Very Good
  • Good
  • Fair
  • Poor

Diamonds that get an excellent grade across all the factors are sometimes referred to as Triple X stones and generally attract a higher premium.

The 4 C’s – Carat

Diamond Carat Weight
Diamond Carat Weight – Image Credit GIA

The last of the 4 C’s is Carat and this is weight, not the size of the Diamond.

This is the universal weight measurement for Diamonds and Gemstones and 1 carat is the equivalent of 0.2 grams.

Carat also plays a big part in a Diamond’s value, just like three other C’s but Diamonds are sold by their weight, with each stone having a price per carat and with all other factors being equal, it is the carat weight that will have the biggest impact on a Diamonds value.

There are certain thresholds that can cause a big increase in a Diamonds price, these are most notable at round numbers such as 1, 2 or 5 carats, for example:

  • Assuming all other factors are equal, a Diamond weighing 1.01 carats will have a much higher price per carat than one weighing 0.98 carats, even though there is basically no difference in the size of the stones

This not only applies to buying a Diamond but also when selling one as well as stones over these thresholds are much easier to sell.

Also be sure to know the difference between total carat weight, often displayed as TCW and the weight of the main stone. If the stone is set with lots of small diamonds, they may advertise the TCW as 1 carat but the main stone may weigh less than half a carat.

What Is The Most Important Of The 4 C’s?

While all of the 4 C’s are important, Cut is arguably the most important as this has a big impact on the look of the Diamond, followed by Clarity, Color and Carat.

But when it comes to buying a Diamond, you should look to get the best balance of the 4 C’s and unless you have a budget to buy the very best, the best balance can be found in:

  • Diamonds with a F, G or H color grade as these are all colorless when viewed through the top of stone
  • A clarity grade of VS1 – SI1 as you won’t be able to see the inclusions in a VS1 or VS2 and the inclusions are generally under the crown facets on an SI1 and depending on their location can be hidden by the setting
  • A cut grade of Excellent or Very Good, some diamonds with a Good cut can look really good but I generally recommend going for higher cut grades.

As for Carat, this will all depend on your budget but a lot of the Diamond buying process comes down to your own personal preference and when it comes to buying your perfect Diamond, buy what YOU like! Not what the salesperson says is the best or what other people like, you will be the one wearing it so make sure you like it before spending your hard-earned money.

Other Diamond Quality Factors

Most posts on the 4 C’s generally stop at the 4 C’s but in the modern world, there is more than just those 4 things to think about when it comes to a Diamonds Quality and I’m going to cover these below.


diamond fluorescence

Fluorescence in a Diamond is something that is misunderstood as there are many people (including people who work in the industry) who believe that having any kind of fluorescence in a Diamond is a bad thing.

But in the majority of Diamonds, fluorescence has no notable impact on the look of the Diamond and without shining a UV light on the stone, you probably wouldn’t have any idea whether the stone has fluorescence or not.

The only time that fluorescence is a negative is when it impacts on the beauty of the Diamond and this sometimes happens in some Diamonds with very strong fluorescence as it can give the stone a milky appearance.


Another quality factor to consider is whether or not the Diamond has been treated as this can have a big impact on the value of the stone as untreated Diamonds are worth considerably more!

But how are Diamonds treated?

Clarity Treatments

Some Diamonds are treated to reduce the appearance of some inclusions but these treatments don’t improve the Diamond’s clarity, they just arguably look better than they did before being treated and there are two main ways this is done:

  1. Fracture filling: this is where they fill any surface-reaching fractures with a high lead content glass, which reduces the appearance of the fracture. The problem is that fracture filling is not a permanent treatment as the glass can be removed from the stone and fracture filled Diamonds aren’t given clarity grades by reputable gem labs
  2. Laser drilling: this is where they drill a laser down to a dark inclusion within the stone and either burn away or bleach the inclusion to make it less visible. But this treatment actually adds another inclusion in the form of the laser drill channel but as this treatment is permanent, laser drilled Diamonds are usually given a clarity grade but it is usually an I grade

On some occasions, both treatments can be done to a Diamond.

Color Treatments

Something that has become more common over the last few years is color treated Diamonds, with two of the most popular ways of doing this being:

  • High Pressure High Temperature (HPHT) – this treatment is often done to natural brown diamonds as the treatment fixes the cause of the brown color and in many cases, the Diamond will be completely colorless after being treated and the color change is permanent
  • Irradiation and Annealing – these treatments are done to create fancy color diamonds, so if you are planning on choosing a pink, blue or orange then always check the diamond report to see if the color is natural. The process involves the diamond first being exposed to radiation which alters the color, commonly to green but also bluish greens and black. If another color is desired then the stone may subsequently be heated to between 500°C and 1200°C to produce yellows, oranges, browns and pinks

But don’t worry, irradiated Diamonds aren’t radioactive once they have been treated.

Treated Diamonds usually cost less than untreated ones but there is good reason for this as there is less demand for them and they can be difficult to resell, which is why I always recommend buying untreated Diamonds, especially for engagement rings.

Lab Reports (Certificates)

While they are often referred to as certificates, the correct terminology is a lab report and it is an important document as they can contain a lot of information about the Diamond, including:

  • Color
  • Clarity
  • Cut
  • Carat
  • Dimensions
  • Origin (mined or lab-grown)
  • Any treatments
  • Fluorescence

And I always recommend buying a Diamond that comes with a report from a reputable gem lab such as the GIA, Gubelin, IGI or HRD as they all have high standards for their Diamond grading and all their staff a experienced qualified gemologists.

GIA Lab Report

But it should be noted that Diamond reports are the opinions of the people who grade the stones and are not facts, which is why they are reports and not certificates.

This is also why if you see the document accompanying a Diamond saying certificate or certificate of authenticity, then you should run away from that stone as quickly as possible!


The 4 C’s are the most important factors when assessing the quality of a Diamond and having a better understanding of what these 4 C’s are and the terminology around them can make the process of learning about or buying a Diamond a whole lot easier.

I'm Paul Haywood FGA DGA, the owner and founder of Haywoods Gems, I'm a fully qualified Gemmologist and Diamond Grader from the Gemmological Association of Great Britain.

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