The Complete Guide to Diamond 4Cs — The Buying Logic Behind Cut, Clarity, Colour and Carat

The first thing you hear when buying a diamond is invariably "the 4Cs". But the 4Cs are not four equal, parallel measures — they have an order of priority. Understanding this order is the key to buying a truly brilliant diamond within your budget.

Cut — The Primary Factor Behind a Diamond's Life

Of the 4Cs, cut is the only factor determined by human craftsmanship, and it is the key driver of a diamond's brilliance. A diamond with excellent colour and clarity but poor cut will lose light through internal reflection, appearing dull and lifeless; conversely, a diamond with an exceptional cut can produce breathtaking fire even if its colour is slightly lower.

GIA grades cut into five levels: Excellent, Very Good, Good, Fair and Poor. CathyPaul's diamond selection standard accepts only the Excellent and Very Good grades, and further quantifies each diamond's light performance using the Sarine Light AI algorithm system, ensuring that the sparkle you see with your own eyes is backed by objective data.

Clarity — Inclusions Seen and Unseen

Clarity measures the distribution of internal and surface imperfections in a diamond. GIA grades clarity from highest to lowest across 11 levels: FL (Flawless), IF, VVS1/VVS2, VS1/VS2, SI1/SI2, and I1/I2/I3. For most consumers, the difference between VS2 and SI1 requires a 10x loupe to detect, and is almost indistinguishable to the naked eye.

Practical buying advice: for an engagement ring's centre stone, VS2 or above is recommended; for earrings, pendants and other pieces worn further from the eye, SI1 already appears clean, allowing you to redirect the budget saved towards carat weight and cut.

Colour — The Philosophy of the D-to-Z Scale

Colour grades range from D (completely colourless) to Z (noticeably yellow), across 23 levels. D, E and F fall within the colourless range; G to J are near-colourless and are almost indistinguishable from colourless diamonds to the naked eye.

In practice, the metal setting affects colour perception. For white gold or platinum settings, G grade or above is recommended to preserve an icy-white appearance; for rose gold or yellow gold settings, H to J grades already present a warm, lustrous colour and can save significantly on cost.

Carat — Weight Is Not Everything

1 carat is equal to 0.2 grams. Carat weight directly affects a diamond's price, but diamonds of the same carat weight can differ in visual diameter by more than 5% due to differences in cut and proportions. We recommend that, beyond carat weight, consumers also pay attention to a diamond's diameter (in mm) — this is the true "size" you actually see when it is worn.

CathyPaul's Diamond Selection Logic

For thirty years, we have upheld the priority order of Cut > Clarity > Colour > Carat when selecting diamonds for our clients. Every CathyPaul diamond comes with a GIA international certificate, and is further authenticated optically by our in-house Sarine Light grading system — so what you are buying is not just a diamond, but a promise that can be scientifically verified.