by Sarah Royce-Greensill

The ‘four Cs’ is an internationally recognised diamond grading system introduced by the Gemological Institute of America in 1953. The four characteristics: carat, cut, colour and clarity, all contribute to a diamond’s beauty and value. When you’re buying a diamond, if you understand the four Cs you’re in the best position to get more bang for your buck.





Carat refers to a diamond’s mass weight, with one carat equal to 200mg. Diamond price increases with weight.  Published weekly, the Rapaport Diamond Report sets out the baseline price-per-carat for diamonds of different cuts, colours and clarity.

Graff oval cut 10.44 carat diamond ring set with pear shape diamond shoulders, POA

Weight doesn’t strictly determine a diamond size, as size is greatly affected by the stone’s cut: whether it’s deep or shallow, for example.




Of the four characteristics, the way a diamond is cut has the biggest influence on its attractiveness. The GIA grades the cut of each diamond on a scale of Ideal, Excellent, Very Good, Good, Fair and Poor, taking into account its proportions and angles, and how well it reflects and refracts light.

Diamonds can be cut and polished into many shapes: round brilliant-cuts are the most common, with emerald (rectangular), princess (square), cushion (rounded square), oval, heart and marquise (a long, pointy oval) shapes also popular.  There are dozens of specialised diamond cuts. Boodles, for example, is the only jeweller in the UK to offer the patented Ashoka cut - an elongated, modified cushion-cut which is said to appear up to 30% larger than its carat weight.

Boodles ashoka cut diamond ring set in platinum with diamond set shoulders, POA

“A diamond owes most of its beauty to nature, but it is the shape and skillfulness of the polished cut that determines that all-important sparkle factor,” explains James Amos, director at Boodles. “Perfect proportions mean more sparkle, it is all about capturing and refracting light.”’





White diamonds are graded on an alphabetical colour scale from D to Z, with D representing pure, colourless white and Z representing a strong yellow hue.

D to F colour diamonds are by far the rarest and, therefore, the most expensive. Lower colour grades are less expensive and therefore it’s possible to buy a larger stone for the same budget.

Most high-end jewellers will only work with diamonds graded from D to G. However others - notably De Beers - work with a greater variety, selecting them for their brilliance and beauty, not just colour rating.

De Beers oval cut 10.1 carat diamond ring set on a platinum solitaire band, POA

“Colour is not a quality, just a degree of rareness,” explains Andrew Coxon, president of the De Beers Institute of Diamonds. “De Beers sees beauty beyond the D to G colour spectrum, to surprise and delight our clients with a bigger diamond that doesn’t break the budget.”



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Clarity refers to the extent of a diamond’s imperfections, graded on an 11-point scale from Flawless to Included.

Imperfections consist of inclusions, which develop within the stone while it is being formed, and blemishes, surface defects created during the cutting and polishing process.

Flawless diamonds have no inclusions or blemishes when viewed under 10x magnification. They are supremely rare and therefore the most expensive. The next clarity grade, Internally Flawless, means that the diamond is free from inclusions but there may be tiny surface blemishes that can be seen under the microscope. These diamonds also carry a significant price premium.

Graff emerald cut 5.25 carat diamond ring set with tapered baguette diamond shoulders, POA

The next clarity grades are Very Very Slightly Included (VVS1 and VVS2), referring to diamonds with tiny inclusions that only a skilled grader can see under a microscope. Then it’s Very Slightly Included (VS1 and VS2), Slightly Included (S1 and S2) and so on. Diamonds rated as Included have imperfections that are visible to the naked eye.

If a diamond is cut well this can mask its inclusions, allowing you to buy a larger stone with a lower clarity grade, without noticing the difference in quality.



Although it’s important to understand these four Cs when buying a diamond, your decision shouldn’t be solely based on a diamond’s certificate.

“We advocate having a very open mind about the four Cs and recommend trying on everything within your budget, regardless of colour, shape, or quality grade,” says De Beers’ Andrew Coxon. “Choosing the diamond that suits you and your budget has much more to do with what the diamond does for your eyes, brain and heart. It is the one which you do not want to take off your hand, regardless of the four Cs.”