Princess cut

It is a square (sometimes slightly rectangular) diamond with a modified brilliant facet arrangement. Gem-A, the gemmological association, says it has an eight-sided table facet with a mixture of triangular, kite-shaped and strip-like facets, and also calls it a "square brilliant".

That makes it different from step cuts such as the emerald cut and the squarer Asscher, which use long step facets and look calmer. The princess offers sparkle together with a strong, bold shape.

Accounts differ, because it grew out of earlier square styles. Gem-A says the princess cut emerged in the 1960s from earlier square diamond styles. The cut was first developed in 1979. Both agree it is a modern shape, newer than the round brilliant and far newer than the old mine cuts behind the cushion. If a seller gives you a single inventor and year, ask where it comes from.

A princess cut is meant to be square. The length-to-width ratio of a square princess should not exceed 1.05, and rectangular princess cuts are commonly no greater than 1.25. A 6.0 x 6.3 mm stone is right at 1.05. The faceting should also mirror itself on both sides, vertically and horizontally, so look for a stone whose pattern is even from corner to corner rather than lopsided.

The sharp corners are the weak point. The corners are best protected by a setting with four V-shaped prongs, eight prongs with two at each corner (split prongs), or a bezel setting. A prong setting with round or claw prongs can work, but V-shaped prongs wrap the point itself.

The trade-off is that a bezel or heavy prongs cover some of the stone's edge.

The pointed corners are good at hiding inclusions, so you can often choose a somewhat lower clarity grade than you would for a step cut. Check where the marks sit and view the stone itself.

GIA also notes that a princess may look slightly smaller than other square diamonds of the same carat weight, because a deep pavilion puts weight below the girdle where you cannot see it from above. Compare millimetres, not just carats.

There is a price angle. You may find princess cuts cost less per carat than comparable round brilliants, because the cutter keeps more of the original crystal. That is a reason to compare quotes, bearing in mind the smaller look. GIA does not give princess cuts an overall cut grade; AGS Laboratories says it has extended its cut grading to princess cuts.

Princess cuts suit solitaires and rings with a square-edged look. A custom engagement ring can be designed with V-prongs from the start, and the design studio is a place to record the shape and style. You can also browse engagement rings or visit a showroom to look at square stones in person.