Diamond Cut

Cut and shape are often spoken of as one thing. They are not. Shape is the outline of a diamond seen from above: round, oval, cushion, emerald and so on. Cut is the quality of the faceting, how precisely the stone has been proportioned, polished and finished, and how well it returns light to the eye. Two round brilliants of identical weight can carry very different cut grades. Cut is the life in the stone, the part you feel before you can name it.

Why cut matters most of the 4Cs

Of the four characteristics that describe a diamond, carat, colour, clarity and cut, it is cut that governs how a stone performs. Colour and clarity set the canvas; cut decides how much light reaches you. A well cut diamond gathers light and sends it back as brightness and flashes of colour. A poorly cut stone of the same weight and grade leaks that light through its base and sides, and looks dull by comparison. A precise cut can also make a stone read brighter and a touch larger for its weight. If your budget is fixed, cut is the characteristic we protect first.

The cut grades

Laboratories grade cut from Excellent down to Poor, with Very Good, Good and Fair in between, weighing proportions, symmetry and polish together. Excellent is the top tier: light return is full and even, and the stone looks crisp from across a room. Very Good sits just beneath it and, to most eyes, is almost indistinguishable in everyday light, while leaving more of the budget for size or colour. We rarely recommend going below Very Good on a round brilliant, because the loss of brightness becomes easy to see. The question is not always whether to buy Excellent, but where it earns its premium and where Very Good is the wiser choice.

Cut and light

The way a diamond handles light can be described in three plain terms. Brilliance is the white light returned to your eye, the overall brightness of the stone. Fire is that light split into spectral colours, the flashes of red, blue and orange you catch when the stone moves. Scintillation is the play of light and dark as the diamond shifts position, the sparkle that makes it look alive. A good cut balances all three; push the proportions too far for one and you lose another.

Cut across shapes

Not every shape is graded the same way. Round brilliants are held to the strictest standard, with full cut grades from Excellent to Poor, because their geometry is consistent and well understood. Step cuts such as the emerald, and fancy shapes such as the oval and cushion, are usually assessed on proportion, symmetry and polish rather than a single headline grade, so the eye of an experienced cutter matters as much as the certificate. We look at length to width ratio, the evenness of the outline and, for ovals, the bow tie, the shadow that runs across a poorly proportioned stone. Read more in our guides to the oval, the cushion and the emerald cut. For an overview of every outline, see our diamond shapes guide.

How we select

Centre stones are available with GIA or IGI certification, and we read those reports closely rather than quoting the grade and stopping there. We source stones to your brief and share full grading and detail, checking proportions against the certificate and setting aside any that look flat. We work with both natural and lab-grown diamonds, and the same standards apply to each. Once a stone is chosen, your ring is designed in CAD and hand-finished at our own bench, with casting and setting carried out by trusted specialist workshops, and the finished ring is hallmarked at the London Assay Office, included.

Good to know

Is cut the same as shape?

No. Shape is the outline, such as round or oval. Cut is the quality of the faceting and light return. A single shape can be cut to many different standards.

Should I always choose Excellent cut?

For a round brilliant, an Excellent or Very Good cut is worth prioritising. Very Good often gives almost the same brightness and frees budget for size or colour. We will share full grading and detail on the difference so you can choose with confidence.

Do fancy shapes have a cut grade?

Round brilliants receive a full cut grade. Step and fancy shapes such as emerald, oval and cushion are judged mainly on proportion, symmetry and polish, so expert assessment matters more than a single grade.

If you would like help choosing a stone whose cut suits your setting and budget, we are glad to talk it through. A free, no-obligation consultation is the easiest place to begin, and you are welcome to read our guide to the 4Cs of diamonds first. We reply within four working hours, Monday to Friday. To arrange a conversation at our studio at The Goldsmiths' Centre, please get in touch.