The 4Cs of Diamonds Explained: Cut, Colour, Clarity and Carat

Lab-created moissanite pieces from our collection — graded on the same principles

Every diamond price tag is built on four measurements — the famous 4Cs, standardised by the Gemological Institute of America (GIA). Understand them and you can read any certificate, compare any two stones, and avoid paying for grades no eye can see. Here they are in plain English.

Cut — the one that makes it sparkle

Cut is not the shape (round, oval, pear) — it's how well the stone's angles and proportions return light. A perfectly cut diamond bounces light back out of the top as brilliance and fire; a poorly cut one leaks light out of the bottom and looks dull regardless of its other grades. GIA grades cut from Excellent to Poor. If you prioritise one C, make it this one: an Excellent-cut stone with modest other grades will out-sparkle a flawless stone cut badly.

Colour — graded by its absence

White diamonds are graded from D (completely colourless) to Z (noticeably yellow-brown). The scale is subtle: D–F are colourless, G–J near-colourless, and most people cannot distinguish a G from a D once the stone is set — despite a large price difference. Yellow-toned metal settings mask warmth even further.

Clarity — the birthmarks inside

Clarity measures internal inclusions and surface blemishes, from FL (flawless) down through VVS, VS, SI to I (included, visible to the eye). The key concept is "eye-clean": most VS and many SI1 stones show no visible flaws without magnification. Paying for VVS or FL buys certainty under a microscope, not beauty on a hand.

Carat — weight, not size

A carat is 0.2 grams of weight. Because price jumps at round numbers, a 0.9ct stone can cost noticeably less than a 1.0ct that looks virtually identical — the classic "buy shy" trick. Halo settings also make centre stones read larger than their weight.

Cheat sheet

C Scale Smart-buyer sweet spot
Cut Excellent → Poor Excellent / Very Good — don't compromise
Colour D → Z G–H (near-colourless, big saving)
Clarity FL → I3 VS1–SI1 if eye-clean
Carat Weight (0.2g each) Buy just under round numbers (0.9, 1.4...)

How this relates to moissanite

Lab-created moissanite — what we sell — is graded with the same vocabulary: our stones are VVS1 clarity and colourless grades, and because they're grown rather than mined, high grades don't carry diamond's rarity premium. That's how a 2ct colourless VVS1 stone can cost a few hundred pounds instead of five figures. Same grading language, different economics — and we always state exactly what the stone is.