How to Choose a Diamond: The 4Cs Explained

Associated with proposals, anniversaries and special moments, the diamond is one of nature's rarest stones. The diamonds in a jeweller's window may look alike at first glance. But choosing a diamond is not just a matter of taste; to understand why a stone costs what it does, you need to know a few basic concepts.

This is where the 4Cs come in, a system accepted worldwide. Made up of Cut, Colour, Clarity and Carat, it defines the basic criteria that set a diamond's characteristics and value. Once you learn to read these four criteria, you can use your budget more wisely and be sure of what you are buying.

Cut: the criterion that sets a diamond's sparkle

Cut is the only one of the 4Cs in the hands of the craftsman rather than nature, and many experts consider it the most important. Cut should not be confused with a diamond's shape (round, princess, pear and so on). Cut refers to the angles of the facets, their symmetry, depth and the quality of the polish. However good its colour and clarity, a badly cut diamond looks dull and lifeless.

A well-cut diamond reflects the light that falls on it inside the stone and sends it back to the eye through the top. If the cut is too deep, light escapes through the bottom and the centre looks dark. If it is too shallow, light leaks out of the sides and the stone looks washed out. That is why it is recommended not to compromise too much on cut when planning your budget.

Colour: grading whiteness

Although most diamonds look colourless at first glance, a large share of natural diamonds contain faint yellow or brown tones. A diamond's colour grade is actually a measure of its lack of colour. The more colourless a stone, the rarer and more valuable it is.

The commonly used colour scale runs from D to Z:

• D, E, F (colourless): The rarest and most expensive group.
• G, H, I, J (near colourless): Their faint warmth is hard to see with the naked eye, especially once set. Often chosen for their balance of price and appearance.
• K, L, M (faint colour): A slight yellowish tone can be seen on close inspection; more affordable.
• N and below: The tone becomes increasingly visible.

The colour of the metal the stone is set in also affects the choice. A yellow gold setting can make a faint warm tone less noticeable. White gold brings out the whiteness of colourless stones. For more on metal colours, see white, rose and yellow gold compared.

Clarity: the marks left by nature

Diamonds form deep in the earth under great pressure and heat. In the process, tiny crystals, specks or fine fractures can remain inside the stone. These natural marks are called inclusions. Clarity shows how free the stone is of them.

Clarity is also graded on an international scale:

• FL / IF: No inclusions visible at ten times magnification, or only tiny surface marks. Very rare.
• VVS1 / VVS2: Very, very slight inclusions, hard to find even at ten times magnification.
• VS1 / VS2: Very slight inclusions, visible under magnification but usually not to the naked eye. A popular group.
• SI1 / SI2: Inclusions easily seen under magnification. SI1 stones mostly look clean to the naked eye; with SI2 inclusions can sometimes be seen.
• I1 / I2 / I3: Inclusions visible to the naked eye that can affect brilliance.

Those who want a good look without straining the budget often choose VS2 or SI1 stones that look clean to the naked eye.

Carat: balancing weight and size

Carat expresses the weight of the stone, not its size. 1 carat is 0.2 grams. A carat is also divided into 100 points; for example, a 0.50 carat diamond is also called 50 points or half a carat.

Because large diamonds are rarer, the price does not rise in proportion to weight; it rises faster. A 1 carat stone of the same colour, cut and clarity usually costs more than twice as much as a 0.50 carat stone.

A badly, shallowly cut stone may look bigger than it is from above, but it looks dull because it does not reflect light well. A well-cut stone just below a round threshold such as 1 carat can look brighter and cost less. You can browse jewellery models in our catalogue.

Why certification matters

Once you know the 4Cs, an important point is whether the diamond has been graded by an independent laboratory. GIA (Gemological Institute of America) and HRD (Antwerp) are among the best known.

These certificates provide an independent record of the diamond's carat, colour, clarity and cut. For large solitaires in particular, choosing independently certified stones is recommended. With stones that only have a document issued by the seller, it can be harder to prove the stone's characteristics if you later want to sell or exchange it.

Which criterion should come first?

Unless your budget is unlimited, you need to balance the four criteria. The common advice is to prioritise cut, because cut determines a diamond's sparkle more than anything else.

For colour, near-colourless grades such as G or H are hard to tell from the top grades with the naked eye and cost less. For clarity, VS2 or SI1 grades that look clean to the naked eye offer a good balance; there may be no need to pay a large premium for an inclusion only visible under magnification. Once these three are balanced, you can choose the carat your budget allows.

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Frequently Asked Questions

Do black specks inside a diamond make it break?

Stones with very low clarity and large inclusions, or inclusions close to the surface, can be damaged more easily by a hard knock. Very small inclusions in grades such as VS and VVS usually do not affect durability.

How can you tell if a diamond certificate is genuine?

Laboratories such as GIA and HRD give each report a unique number. You can check the report details by looking up this number on the laboratory's official website. On some stones this report number is also laser-inscribed on the girdle.

Why do diamonds lose value when sold?

Diamonds also have a gap between buying and selling price, and the design and craftsmanship of the jewellery are not refunded when sold. Independently certified stones usually find buyers more easily because their characteristics are documented.