(618) 681-5688

— by Cullen Jewellery — Reading time 8 minutes

The 4Cs of Diamonds

What are the 4Cs of Diamonds?

Just like any two people, no two diamonds are alike; the facets of variation between each stone make each diamond’s beauty distinct.

Gemological labs such as GIA (Gemological Institute of America) and IGI (International Gemological Institute) use a universal system to describe a diamond’s appearance and officially grade its quality. A diamond’s grade is determined by the 4Cs: cut, colour, clarity, and carat.

Several factors determine the beauty of a diamond and contribute to its value. Understanding the 4Cs, and knowing what to look for in a stone, can help you to ensure your diamond is as beautiful as it is valuable.

The 4Cs of Diamonds

The 4Cs — cut, colour, clarity, and carat — are the four defining factors that determine a diamond’s grade. These characteristics describe diamonds in terms of their appearance — from their lustre to their sparkle — and also help to determine their price point.

It's important to consider the 4Cs when purchasing a diamond, because many of the factors that affect its value might not be apparent at first glance. For diamonds sold online, it can be even trickier to understand the value of a diamond from just a photograph, and it's best to check its grade to make sure you're making a fair purchase.

Let’s take a closer look at each of these categories:

Diamond Cut

A diamond’s cut refers to the balance of proportion, polish, and symmetry it possesses. Cut is the difference between a round brilliant diamond and a step cut emerald diamond. But cut is different to diamond shape, which dictates the overall silhouette of the stone. Cut is more about what's on the inside.

The way a diamond’s facets are cut will affect its light performance — or, in other words, how sparkly, bright, and reflective it is. Diamond quality really depends on cut. In fact, a diamond’s cut is arguably the most important category when determining the stone’s value.

The facets of a diamond bounce, scatter, and reflect light to create myriad effects. Each facet pattern creates something special, unique, and a little bit magical. That’s why jewellers have to be part artist, part mathematician, and part spellbinder — using precisely cut angles to create dazzling results.

A well-cut stone will reflect light straight up through its crown (its upper facets), displaying that characteristic, scintillating appearance diamonds are valued for.

If a diamond’s cut is too deep, shallow, or out-of-proportion, light can leak out of the pavilion facets (lower facets) of the stone, reducing its sparkle and making it appear dull.

A diamond’s cut is graded on a ten-point scale ranging from Poor to Ideal. At Cullen Jewellery, we exclusively stock diamonds that have an Excellent to Ideal Cut.

Diamond halo engagement ring. Source: Cullen Jewellery
Loose pear, oval, and round stones. Source: Cullen Jewellery
Round brilliant cut stone viewed from the side. Source: Cullen Jewellery

Diamond Colour

Emerald and oval stones. Source: Cullen Jewellery
Carmen ring, from the For Self collection. Source: Cullen Jewellery

Colour refers to the natural presence or lack of colour visible within a diamond. If a diamond appears cloudy or slightly yellow, it is said to have more colour. Typically, the clearer (or more colourless) the stone is, the higher its value.

Colour is usually an indication that different trace elements were present when the diamond was being formed.

Diamonds with more colour will exhibit a pale yellow or pale brown tint, which reduces their colour grade and value.

Subtle colour won’t always take away from the beauty of a diamond — it may even make it more unique. However, the more colour a diamond has, the more difficult it is for light to pass through it, which can result in a dark or dull stone.

When light enters a clear and colourless stone — it passes through easily, resulting in more fire and more brilliance.

In terms of colour, lab grown diamonds are in a completely different playing field to mined diamonds. In the controlled conditions of a laboratory, the mineral contamination that causes colour in a diamond is unlikely to happen.

Every diamond is professionally evaluated and graded according to a GIA scale ranging alphabetically from D (colourless) to Z (light colour). While mined diamonds can fall anywhere on this scale, lab grown diamonds are usually graded J (near colourless) or clearer.

Diamond Colour Grades


Absolutely Colourless or Icy White: The highest colour grade — extremely rare and the most expensive.


Colourless: Only minuscule traces of colour can be detected by an expert gemologist— a rare, high-quality diamond.


Colourless: Slight colour detected by an expert gemologist, but still considered a “colourless” grade — a high-quality diamond.


Near Colourless: Colour noticeable when compared to diamonds of better grades, but offers excellent value.


Near Colourless: Colour noticeable when compared to diamonds of better grades, but offers excellent value.


Near Colourless: Slightly detected colour — a good value.


Near Colourless: Slightly detected colour — a good value.

Diamond Clarity

Clarity refers to how clear and pure a diamond is. Purity is graded according to the number of imperfections or inclusions present within a stone.

When a diamond is growing, it is extremely common for microscopic impurities to become trapped within the diamond or on its surface.

Though typically only visible under 10x magnification, a diamond’s imperfections are used to measure its clarity and will impact its overall value. A diamond with fewer imperfections will come at a higher asking price. Make sure to check a diamond’s certificate before you make a purchase, as the reason it is valued at a certain price point may not always be obvious to the naked eye.

Imperfections also give each diamond its own unique character, and to many, these add to its beauty.

There are eleven clarity grades, ranging from Flawless (FL) to Included (I3). At Cullen Jewellery, our gemstones are exclusively Very Very Slightly Included (VVS1-2) or clearer — which means each stone possesses a piercing sparkle.

Solitaire diamond engagement ring. Source: Cullen Jewellery
Brilliant cut loose stone. Source: Cullen Jewellery

Diamond Clarity Grades


Flawless: Diamonds with no internal or external imperfections. These are incredibly rare and valuable.


Internally Flawless: No internal flaws.


VVS1 (Very Very Slightly Included 1): Any inclusions are difficult to see under 10x magnification.


Very Very Slightly Included 2: Slightly more inclusions than VVS1 but still very difficult to see under 10x magnification.


Very Slightly Included 1: Difficult to see inclusions under 10x magnification but typically cannot be seen with the naked eye.


Very Slightly Included 2: Slightly more inclusions than VS1 but still difficult to see inclusions under 10x magnification and typically cannot be seen with the naked eye.


Slightly Included 1: Inclusions are visible under 10x magnification but may not be very visible to the naked eye.


Slightly Included 2: More inclusions than SI1. Inclusions are visible under 10x magnification but may not be very visible to the naked eye.

Diamond Carat

Oval diamonds tend to appear larger than their carat weight suggests. Source: Cullen Jewellery

Carat (ct) refers to the specialised unit of measurement that applies to the weight of diamonds and other gemstones.

It’s important to note that carat weight doesn’t always correlate with the size of a gemstone. Various cuts and shapes distribute carat weight differently within a stone — which means that some diamonds will appear much larger than their carat weight suggests. For this reason, the size of a gemstone is measured separately to carat, by length and width in millimetres. Therefore, an emerald-cut diamond and a round-cut diamond with the same carat weight will have different size measurements in millimetres.

Typically speaking, the larger the diamond, the rarer and more valuable it is. For mined diamonds this is certainly the case — to retrieve one carat of mined diamond, miners have to sift through around 250 tons of ore, making extracting diamonds a costly and labour-intensive process.

With the emergence of lab grown diamonds as an alternative to mined diamonds, a one-carat diamond can be grown in a lab and sold at a fraction of the cost of a mined one.

Lab grown diamonds are grown in a controlled environment that mirrors the heat and pressure conditions that create diamonds in the earth's crust. They are the same as mined diamonds in their physical and chemical properties — the only difference is their origin.

Lab grown diamonds are also graded according to the 4Cs, and their price point will reflect their cut, colour, clarity, and carat.

When determining a diamond’s value, it’s important to know about the 4Cs. Diamonds vary a lot in their appearance, so choosing one can feel difficult without some kind of objective guide on what to look for. However, the 4Cs are in no way 'buying rules,’ nor are they a definitive list of what makes a diamond beautiful. The beauty of each diamond is yours to decide — that's what makes it special.

Frequently Asked Questions

Your questions, answered.

What you find beautiful about a particular diamond is up to you. But in terms of sparkle, cut and clarity are going to have the biggest influence. Experienced diamond cutters are well aware that a diamond’s angles — on the inside of the stone — reflect and scatter light and contribute to the diamond’s brilliance. And imperfections in a low clarity diamond can block light and affect its sparkle.

Diamonds bought from reputable diamond sellers will always come with a certificate. If a jeweller can’t provide a diamond certificate, it is difficult to determine the value of your diamond, and it’s best to look elsewhere.

Yes! The GIA diamond grading system is universal, and the categories remain the same: carat and cut. Color and clarity. However, you may have spotted the different spelling of color. Clarity, carat, and cut stay the same.

Explore Our Lab Grown Diamond Engagement Rings Visit Our Showroom