The 4 Cs of Diamonds

Every certified diamond is graded on four independent characteristics: cut, colour, clarity and carat weight. Together they describe the stone completely — and they are the reason two diamonds of the same size can differ in price by a factor of ten.

Three of the four are set the moment the crystal forms. Only one, cut, is decided by human hands. That distinction matters more than any other when you are choosing a stone.

Cut grade describes proportion, symmetry and polish, not the shape of the stone. It measures how effectively the facets catch light, bounce it internally and return it through the top of the diamond. Cut too shallow or too deep and light escapes through the bottom, leaving the stone dull however good its other grades are.

Cut is where we would never economise. An Excellent or Very Good cut in a modest colour grade consistently outperforms a Good cut with a premium colour grade — and the difference is obvious across a room, not just under a loupe.

Diamond colour is measured by how little colour is present. The scale runs from D, wholly colourless, through to Z, a light yellow or brown tint. Grading is done face-down against a controlled white background, which is a far harsher test than how a stone is actually worn.

Where the value sits

G through J is the practical sweet spot. Set in white gold or platinum these stones read as white to the unaided eye, yet cost materially less than D–F. If the setting is yellow or rose gold you can drop further still — the metal reflects warmth into the stone, so a K or L grade looks entirely at home.

Clarity records the internal features (inclusions) and surface features (blemishes) that formed as the crystal grew. Grading is carried out under 10× magnification, so a great many stones that grade well short of flawless are entirely clean to the naked eye.

The term to know is eye-clean: no inclusions visible to the unaided eye at normal viewing distance. VS1 and VS2 are reliably eye-clean, and a great many SI1 stones are too, depending on where the inclusions sit. Paying for VVS or flawless buys certificate prestige rather than a visible difference.

One carat is 0.2 grams, divided into 100 points. It is critical to understand that carat measures weight, not visual size. A deeply cut stone carries weight in its belly where nobody sees it, while a well-proportioned stone spreads the same weight across a wider face-up surface and looks larger.

Buying just under the milestones

Prices jump sharply at round numbers, particularly at 0.50, 1.00 and 2.00 carats. A 0.92 carat stone is visually indistinguishable from a 1.00 carat but can cost considerably less. Shopping just below a threshold is the single easiest saving available.

A grading report from an independent laboratory is what turns those four letters and numbers into something you can rely on. It records the 4 Cs alongside measurements, proportions, fluorescence and a plotted diagram of the stone’s inclusions.

We certify through IGI, GIA and HRD. Whichever laboratory issues the report, check that the report number is laser-inscribed on the girdle of the stone, and verify that number on the laboratory’s own website rather than trusting a printed copy alone.