A diamond’s face-up shape is called its girdle outline. Girdle outline usually doesn’t affect the appearance of a round brilliant unless it’s really irregular. Round brilliants generally have balanced outlines, and usually deliver attractive brightness, fire, and scintillation.
With fancy shapes—all shapes other than round—not all stones of a given shape are equally attractive. Table size, crown angle, and pavilion depth have something to do with this, of course, but it also depends on how pleasing the shape’s girdle outline is.
An evaluation of girdle outline also involves other, more practical considerations. For example, shape itself can make a difference: A bench jeweler might have a difficult time setting a stone with an unusual shape.
Visual appeal and practical considerations often work together to result in a diamond that’s both beautiful and durable. Rectangular cuts, for example, have beveled corners for a variety of reasons. First, beveled corners add visual appeal: They give a dynamic quality to what would otherwise be a plain rectangle. They’re also practical: They provide a secure setting area for prongs and make the stone less vulnerable to chipping. The size of the beveled corners matters, too. If they’re too narrow, they give the stone an odd look and make it difficult to set.
Shoulders are located near both ends of oval shapes and near the rounded end of pear shapes. They should be gently and evenly rounded. Squaring the shoulders makes the diamond weigh more, but it makes pears look triangular and ovals look chunky. In the same way, a distorted curve on the lobes of a heart can make it look squashed or flat.
On marquises, pears, and hearts, the sides near the points are called wings. They should form attractive arches. If they’re too flat, they make the stone look too narrow. If they’re too rounded, they make it look short and stubby.