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A diamond’s cut is the quality of its proportions, symmetry and polish. It decides how light travels through the stone and returns to your eye, so it has more effect on sparkle than any other grade. A well-cut diamond looks bright and lively; a poorly cut one can look dull or dark, whatever its colour, clarity or weight. Our laboratory-grown diamonds are cut and polished in Surat, where most of the world’s diamonds are cut.
Cut and shape are not the same
- Shape is the outline of the diamond: round, oval, pear, princess and so on.
- Cut is how well that shape has been proportioned and finished.
For example, two round diamonds can have the same shape but very different cut grades, and look very different on the hand.
Cut grades explained
| Grade | What it means |
|---|---|
| Excellent (often called Ideal) | Precise proportions, symmetry and polish; returns almost all the light that enters for the most brilliance and fire |
| Very Good | Returns most of the light; very close to Excellent in appearance and often better value |
| Good | Returns a good share of the light; a balance of budget and beauty |
| Fair | Noticeably less brilliance; chosen when size matters more than sparkle |
| Poor | Too deep or too shallow, so light escapes and the diamond looks dull |
We focus on Excellent and Very Good cuts. If you add an IGI report at checkout, it records your diamond’s cut, polish and symmetry.
What makes a good cut
- Proportions: the depth of the diamond and the size of its top facet (the table) in relation to its width. A diamond cut too deep leaks light through the sides; one cut too shallow leaks it through the bottom.
- Symmetry: how precisely the facets line up and match each other.
- Polish: how smooth the facet surfaces are.
How diamonds are cut
- Planning: the rough diamond is mapped to find the shape that gives the best yield and the fewest visible inclusions.
- Sawing or cleaving: the rough is divided, today usually with a laser.
- Bruting: the outline is shaped, for example into a round.
- Polishing: the facets are ground and polished at exact angles.
- Inspection and grading: the finished diamond is checked and graded.
Brilliant cuts and step cuts
- Brilliant cuts (round, oval, pear, marquise, heart, princess, cushion and radiant) have many triangular and kite-shaped facets for maximum sparkle.
- Step cuts (emerald and baguette) have long, parallel facets like steps, for a calm, mirror-like look that shows clarity.
Read about each shape in our diamond guide, or see them in our engagement rings.
Frequently asked questions
Why do fancy shapes have no cut grade?
Laboratory cut grades are standardised mainly for round brilliant diamonds. Fancy shapes such as oval, pear, emerald and princess are judged on their proportions, polish and symmetry instead.
Why do round diamonds cost more than other shapes?
Cutting a round brilliant loses more of the rough diamond, and it takes great precision, so a round diamond costs more per carat; it is also the shape with the most sparkle.
Which cut sparkles the most?
A round brilliant with an Excellent cut grade.
Which diamond shape looks biggest?
Elongated shapes such as oval, marquise and pear look larger than a round diamond of the same carat weight.
Which cut grade gives the best value?
Very Good looks almost the same as Excellent to the eye and usually costs a little less. We do not recommend going below Good.
