Diamond shape guide.
Shape is the first decision and the most personal one — it is the part of a diamond anyone will actually recognise. It also changes what the other grades need to be, how large the stone looks for its weight, and what it costs.
Round brilliant, by design.
Oval, pear and marquise.
Emerald and Asscher — go a clarity grade higher.
Three
families.
Ten shapes, but only three ways of faceting them. Knowing which family a shape belongs to tells you most of how it will behave.
Facets arranged as triangles and kites, designed to break light up and throw it back at you. These are the shapes that sparkle — scintillation is the trade word — and they hide inclusions well, because the flashing gives the eye nowhere to settle.
Long parallel facets running in rows, like steps. Instead of sparkle you get broad flashes of light and a view straight down into the stone. Cleaner, more architectural, and far less forgiving — an inclusion a brilliant would hide is plainly visible here.
A square outline with brilliant faceting underneath. It keeps more of the original rough than a round does, which is why it costs less per carat for comparable grades.
All ten,
compared.
The character of each cut, the ratio band worth aiming for, and the one thing to protect when you buy it.
Maximum brightness and fire; the benchmark every other cut is judged against.
Cut is the grade to protect here. An Excellent-cut G will outshine an Ideal-cut D that has been cut deep to save weight, and it will cost less. Buy the cut first, then spend what is left on colour.
Soft outline, broad coloured flashes, and a vintage feel that suits antique settings.
Decide between crushed-ice and chunky before you shop; they are not interchangeable and the report does not distinguish them. Cushions also hide colour well, so a warmer grade goes further here than in a round.
Restrained, architectural flashes rather than sparkle; unforgiving of inclusions.
Clarity is the grade to protect. Those open planes show inclusions a brilliant cut would swallow, so VS2 is a sensible floor here where SI1 would pass in a round. Colour also shows more readily.
A tapering, directional outline that elongates the hand.
Check symmetry closely — the two shoulders should mirror each other and the point should sit dead centre on the axis. An asymmetric pear is obvious once seen and cannot be unseen.
Concentric step facets that read as a corridor of mirrors; pure Art Deco.
As with the emerald cut, clarity and colour show plainly through the open steps. VS2 and H are sensible floors. Check that the concentric squares are properly aligned; poor symmetry ruins the corridor effect.
Crisp square outline with brilliant-cut fire; the best value per carat.
Insist on a setting with protected corners — V-prongs or a bezel. A princess set with the corners exposed will chip eventually, and a chipped corner cannot be polished out without recutting the stone.
Brilliant-cut sparkle in an outline that wears larger than its weight.
Every oval has some bow-tie. Look at the stone in video, not on paper — the grading report will not mention it. A faint, even shadow is normal; a hard black bar across the waist is not.
The most difficult outline to cut well, and unmistakable when it is.
Do not buy a heart under 0.75 ct — the shape simply does not read at smaller sizes, particularly once prongs cover part of the outline. Symmetry matters more than any other grade on this shape.
The largest visual spread per carat, with a distinctly period outline.
Both points need prongs, and both halves must match. Watch for the bow-tie, which tends to be more pronounced in a marquise than in an oval because the stone is longer.
Emerald-cut outline with brilliant-cut fire; forgiving of inclusions.
Because radiants concentrate colour, a warmer grade shows more here than in a round. If you are buying colourless, hold to H or better; if you are buying fancy yellow, the same trait works in your favour.
Choosing
between them.
Four questions that narrow ten shapes down to two or three faster than anything else.
Elongated shapes — marquise, pear, oval, emerald — spread more of their mass across the top, so they face up bigger than a round of the same carat weight. If size is what you want, they are the efficient way to get it.
Brilliant cuts, comfortably. Their faceting is busy enough that the eye does not settle. Step cuts show everything, so on an emerald or Asscher we would go a clarity grade higher than we otherwise might.
Any shape with a point — pear, marquise, heart, princess — has a corner that can chip. A setting that covers the point is not optional on those, it is the setting.
Princess, cushion and radiant, because they waste less rough. Round costs most: roughly a third of the crystal is lost getting there, and demand has never dropped.
Asked about
shapes.
The round brilliant, and it is not an accident — its facet pattern was worked out mathematically to return as much light as possible. Every other brilliant cut is a variation on it. Step cuts are not trying to sparkle at all; they trade scintillation for broad, clean flashes.