The 4Cs — Your Complete Diamond Guide

Cut is the single biggest factor in how beautiful a diamond looks. It is not about the shape of the diamond — it is about how precisely the diamond has been faceted to interact with light. A perfectly cut diamond takes incoming light, bounces it between its facets, and returns it through the top of the stone in an explosion of brilliance and fire. A poorly cut diamond, even with excellent colour and clarity, will look dull and lifeless.

Cut is graded on three key visual properties: brilliance (white light reflected), fire (dispersion of light into rainbow colours), and scintillation (sparkle when the diamond moves).

Cut also encompasses three technical measurements: table percentage (the size of the flat top facet relative to the diamond's width), depth percentage (how deep the stone is relative to its width), and polish and symmetry. These numbers are all recorded on your IGI certificate.

Diamond colour actually measures the absence of colour. The most prized diamonds are completely colourless — graded D on the GIA/IGI scale — because they allow the most light to pass through and create maximum brilliance. As you move down the scale toward Z, diamonds show increasing warmth — faint yellows and browns that become visible to the naked eye.

The colour scale runs from D (colourless) to Z (light yellow/brown). Most diamonds sold in fine jewellery fall between D and J.

Clarity measures the presence of natural imperfections — called inclusions (internal) and blemishes (external). Almost every diamond has them. They are formed during the diamond's creation deep within the earth and are essentially nature's fingerprint — unique to each stone.

Clarity is graded under 10x magnification. The grades range from Flawless (no inclusions visible under magnification) to Included (inclusions visible to the naked eye).

Carat is the most straightforward of the 4Cs — it is simply the weight of the diamond. One carat equals 200 milligrams. Larger diamonds are rarer and therefore more valuable per carat — a 2-carat diamond does not cost twice as much as a 1-carat diamond; it can cost four or five times as much because of the exponential rarity increase.

An important distinction: carat measures weight, not size. Two diamonds of the same carat weight can appear very different sizes depending on their cut proportions. A well-cut diamond maximises its face-up appearance, while a poorly cut stone may carry its weight in depth — appearing smaller from above.

The art of buying a diamond is understanding how to balance the 4Cs within your budget. You rarely need to maximise all four — and trying to do so will either price you out or lead to overpaying for qualities you cannot see.