Jewellery

The Four Cs of Diamonds Explained: Carat, Cut, Colour and Clarity

11 November 2025

Katie Miller

Buying a diamond can feel overwhelming. Whether you're searching for an engagement ring, evaluating a family heirloom or considering a purchase at auction, you'll quickly encounter a term used throughout the jewellery industry: the Four Cs.

Developed by the Gemological Institute of America (GIA), the Four Cs provide a framework for assessing a diamond's quality and value. They refer to carat, cut, colour and clarity.

While these characteristics help specialists compare diamonds, they are not a formula for determining whether a diamond is "good" or "bad". Some collectors prioritise size, others favour colour, while many are drawn to antique cuts that would not achieve top grades by modern standards.

Understanding the Four Cs is therefore less about finding the perfect diamond and more about finding the right diamond for you.

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What Are the Four Cs of Diamonds?

The Four Cs are the internationally recognised system used to evaluate diamonds.

C	What It Measures	Why It Matters
Carat	Weight	Influences rarity and value
Cut	Quality of faceting	Affects brilliance and sparkle
Colour	Presence of colour	Impacts appearance and rarity
Clarity	Internal characteristics	Influences transparency and value

Each category contributes to a diamond's overall appearance, but no single factor should be considered in isolation.

THE FOUR Cs

Carat: Understanding Diamond Weight

Carat is often the first characteristic buyers ask about, but it is also one of the most misunderstood.

A carat is a unit of weight equal to 0.2 grams. The term originates from the seeds of the carob tree, which were historically used as counterweights for measuring gemstones.

While carat weight contributes significantly to value, it does not necessarily determine how large a diamond appears when worn.

Two diamonds of identical weight can look very different depending on their proportions and cut. A deeper stone may carry more of its weight below the surface, while a shallower stone may appear larger when viewed from above.

This is why carat weight should always be considered alongside cut and overall proportions.

Does a Higher Carat Mean a Better Diamond?

Not necessarily. A well-cut 1.50-carat diamond may appear more impressive than a poorly cut 2-carat stone. Carat contributes to rarity, but beauty depends on a combination of factors.

THE FOUR Cs

Clarity: What Are Diamond Inclusions?

Clarity refers to the internal characteristics present within a diamond.

As diamonds form deep within the Earth under intense heat and pressure, tiny crystals, mineral deposits and structural features can become trapped inside them. These natural characteristics are known as inclusions.

Far from being flaws in the everyday sense, inclusions are evidence of a diamond's geological formation.

To assess clarity, gemmologists examine diamonds under 10x magnification and assign a grade according to the GIA grading system.

Diamond Clarity Grades Explained

Grade	Meaning
FL	Flawless
IF	Internally Flawless
VVS1-VVS2	Very Very Slightly Included
VS1-VS2	Very Slightly Included
SI1-SI2	Slightly Included
I1-I3	Included

Many inclusions are invisible to the naked eye. In practice, a VS or SI diamond may appear completely clean when worn.

Which Clarity Grade Should You Choose?

The answer depends on personal preference.

Some buyers seek the highest possible clarity grades, while others prioritise size, colour or cut. Many diamonds with visible inclusions remain beautiful and highly desirable.

THE FOUR Cs

Cut: The Character of a Diamond

‘Round’ is the shape of the diamond and ‘brilliant’ is the faceting style. A diamond's cut grade is determined by how well the facets are placed by the artisan. It shows how well the diamond was cut.

Diamond cutting is an art in and of itself. The rough material is rarely uniform and seeing its potential takes practice and skill. Diamonds are an unforgiving material and once a portion is cut off or polished out, it cannot be replaced. The quality of the cut is responsible for much of the beauty of a faceted diamond and is one of the most complex and technical aspects of the Four Cs.

While this certainly seems like a heavy topic, the real judge of the quality of the cut of a diamond is the viewer. There are ratios and equations that one can follow to determine if what they are looking at is a technically top-quality cut, however, the quality of faceting is apparent when the diamond is examined. A poorly cut diamond will look it.

When judging cut, the variables one should consider are brightness, fire, and scintillation.

Brightness is the white light that is reflected from a diamond. This is the light that is reflected both internally and externally and gives the white flash when light hits a diamond.

Fire is the refractive quality of a diamond when it splits light. This is what causes the tiny rainbows one might see when looking into a diamond.

Scintillation is sparkle and is caused by well-placed facets bouncing light around the inside of the diamond.

All these variables can be judged from a diamond’s face-up appearance. When a diamond is of poor cut it will appear dull or have heavy ‘extinction’ which is when light passes through a diamond without reflecting out and occurs when facets are improperly placed.

Diamond shapes that are particularly difficult to facet well are pear and oval cuts. These elongated shapes can have what are termed ‘bow-ties’ which are points of extinction that look like a bow-tie through the centre of the diamond. Bow-ties have minimal scintillation and can appear grey.

The best way to judge if a diamond is well cut and faceted is to look down at the top, rock the gem back and forth, and see how it catches and reflects the light. The most important thing to consider though, is personal preference.

Some faceting styles emphasise fire over brightness, for those who prefer the rainbow flash, while others focus more on scintillation. When purchasing a diamond either for oneself or for another person, determining personal preference and developing an opinion for the type of sparkle is just as important as having a preferred shape.

THE FOUR Cs

Colour

This is perhaps the simplest of the Four Cs as it is exactly what it sounds like. This is the colour of the diamond. The colour scale for diamonds ranges from D to Z. D represents colourless and Z represents the most colour-saturated a diamond can be without being a ‘fancy colour’.

Traditionally, colour is graded when a diamond is unmounted. The gem is placed against a white card or compared against a set of masterstones that represent the various tones in the scale.

The colour of a diamond can only be accurately graded when it is outside of its jewellery mounting because the colour of the surrounding metal can influence the apparent colour of the diamond. When purchasing a diamond, it is therefore important to consider the final look of the jewellery, yellow-toned diamonds appear warm and buttery when worn in yellow gold but show out as off-white when worn in either white gold or platinum.

Fancy-coloured diamonds are what we think of as Canary Yellow or even Pink. Diamonds are one of the few gemstones that come in a full rainbow spectrum of colour and fancy-coloured diamonds have their own grading system. Personal preference is one of the most important factors to consider when judging colour, while D is at the top end of the colour scale, fancy-coloured diamonds can sell for extremely-high prices and low-toned diamonds have their own warm charm.

Which of the Four Cs Is Most Important?

There is no universal answer.

For many collectors:

Cut has the greatest impact on appearance.
Carat has the greatest impact on rarity.
Colour influences overall character.
Clarity becomes important once inclusions are visible.

The ideal balance depends entirely on individual priorities.

Buying Diamonds at Auction

One of the advantages of buying diamonds at auction is the opportunity to compare different stones, cuts and styles side by side.

Auction specialists can provide guidance on diamond grading, condition and value, helping buyers understand how the Four Cs apply to individual pieces. Importantly, auction buying also encourages collectors to look beyond certificates and grades. Exceptional craftsmanship, period design, provenance and individuality can be just as significant as technical specifications.

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Diamond Jewellery FAQs

Carat, cut, colour and clarity.

Many specialists consider cut to have the greatest impact on appearance.

No. Proportions and cut influence apparent size.

Some can, but many are invisible to the naked eye.

Generally yes, although rare fancy-coloured diamonds can be worth significantly more.

The Four Cs of Diamonds Explained: Carat, Cut, Colour and Clarity

Discover our Jewellery Department

What Are the Four Cs of Diamonds?

Carat: Understanding Diamond Weight

Does a Higher Carat Mean a Better Diamond?

Clarity: What Are Diamond Inclusions?

Diamond Clarity Grades Explained

Which Clarity Grade Should You Choose?

Cut: The Character of a Diamond

Colour

Which of the Four Cs Is Most Important?

Buying Diamonds at Auction

Looking to Buy Diamond Jewellery at Auction?

Katherine Miller

Diamond Jewellery FAQs

What are the Four Cs of diamonds?

Which of the Four Cs is most important?

Does a higher carat diamond always look larger?

Can diamond inclusions be seen without magnification?

Are colourless diamonds more valuable?