The Diamond Guide

Every diamond is described by four qualities: cut, colour, clarity and carat. Together they decide how a stone looks and what it costs. No single C matters on its own; the art is finding the balance that looks best for your budget.

Cut is how well a diamond's facets are shaped and angled to return light. It matters most, because it controls sparkle. A well-cut stone can look brighter and even larger than a heavier, poorly cut one.

• Excellent or Ideal: the most brilliance. Our recommendation for round stones.
• Very Good: close to Excellent and often better value.
• Good and below: noticeably less sparkle.

White diamonds are graded from D (completely colourless) to Z (light yellow or brown). The differences between neighbouring grades are subtle and hard to see once a stone is set.

• D to F: colourless. The rarest and most expensive.
• G to H: near colourless. Looks white in platinum or white gold, and a favourite for value.
• I to K: faint warmth, which disappears in yellow or rose gold.

Clarity describes tiny natural marks inside or on the surface of a stone. Most are invisible without magnification.

• FL, IF: flawless or internally flawless.
• VVS1, VVS2: very, very slightly included.
• VS1, VS2: very slightly included.
• SI1, SI2: slightly included.
• I1 to I3: included, often visible to the eye.

For most shapes, a stone that looks clean to the naked eye (often VS2 or SI1) gives the best value. Emerald and Asscher cuts show more of the inside of the stone, so we suggest VS1 or higher for those.

Carat is weight, not size. One carat is 0.2 grams. Two stones of the same weight can look different sizes depending on their cut and shape.

Prices step up at popular weights like 1.00, 1.50 and 2.00 carats. A stone just under, such as 0.90 carats, looks almost identical once set and can cost noticeably less.

Lab-grown diamonds are real diamonds. They have the same chemical makeup, hardness and sparkle as natural diamonds; the only difference is where they formed.

• Natural: formed deep in the earth over billions of years. Rarer, and generally hold their value better.
• Lab-grown: created in a laboratory. Usually a fraction of the price, so you can choose a larger or higher-grade stone for the same budget.

Both are graded by independent labs, and the grading report states whether a stone is natural or lab-grown. We'll show you both side by side so you can decide.

Diamonds also come in pink, yellow, blue, champagne, cognac, green and black. Natural coloured diamonds are rare and priced by the strength of their colour, from Fancy Light up to Fancy Vivid. Lab-grown coloured diamonds offer the same look at a much more accessible price.

• Round: the most sparkle of any shape, and a timeless choice.
• Oval, pear and marquise: elongated shapes that look larger for their weight and lengthen the finger.
• Emerald and Asscher: step cuts with long, mirror-like flashes. Elegant and understated.
• Cushion and radiant: softened corners with lots of fire.
• Princess: a crisp square with a modern look.

For any significant stone, ask for an independent grading report, such as from GIA or IGI. It confirms the 4Cs and whether the stone is natural or lab-grown. Many stones also carry a microscopic laser inscription on the edge that matches the report number.