BEYOND THE 4CS
Cut is the one C made entirely by human hands, and it decides how much a diamond sparkles. What the cut grade measures, why fancy shapes have none, and how to judge a cut for yourself.
Colour, clarity and carat are largely set by nature. Cut is decided by the cutter. It determines how light enters a diamond, travels through it and returns to your eye, and so how bright and lively the stone looks.
A diamond with fine colour and clarity can look dull if it is poorly cut. A beautifully cut diamond with more modest grades can outshine it across the room. If you prioritise one C, make it cut.
For a standard round brilliant, GIA grades cut from Excellent to Poor. The grade weighs how the diamond looks and how it is made:
| Grade | What to expect |
|---|---|
| Excellent | The highest brightness, fire and scintillation; the grade we recommend for a round |
| Very Good | Very close to Excellent; differences are subtle |
| Good | Noticeably less light return |
| Fair | Light escapes through the sides or bottom; looks dull |
| Poor | Little life; not suitable for an engagement ring |
Other laboratories use their own scales, and some use terms such as Ideal. Always read the cut grade alongside the laboratory that issued it.
GIA gives an overall cut grade only to round brilliants. Ovals, pears, cushions, emerald cuts and other fancy shapes vary too much in outline for a single standard, so their reports show polish and symmetry but no cut grade.
For these shapes, cut is judged by the proportions and by eye. Look for an outline you love, an even spread of light across the face, and the length-to-width ratio that suits your taste.
Ovals, pears and marquises can show a bow-tie, a dark band across the centre where light leaks out. A faint bow-tie is normal and adds contrast; a heavy one that stays dark as the stone moves is a sign to look elsewhere.
Check the stone face up and as it tilts. A well-cut fancy shape stays bright across its whole face, with no dead or glassy areas, and its outline is crisp and symmetrical.
For a round brilliant, choose Excellent cut, ideally with Excellent polish and symmetry. For any other shape, never buy from the numbers alone. We check every fancy-shaped stone by eye, in person or on video, before we propose it.
Excellent, the highest grade on the GIA scale for round brilliant diamonds. It gives the strongest brightness, fire and scintillation.
A Very Good round can look very close to Excellent. For an engagement ring we recommend Excellent, because cut has the largest effect on sparkle.
GIA gives an overall cut grade only to round brilliants. Fancy shapes are judged by their proportions, polish, symmetry and appearance.
A darker band across the centre of an oval, pear or marquise diamond. A faint one is normal; a heavy one reduces brightness.
For appearance, yes. Cut decides how much a diamond sparkles, while most clarity differences above SI are not visible to the eye.
STILL HAVE QUESTIONS?
Bring the report, or the question, to a private appointment in central London or a video call. Consultations are complimentary.