Bow-tie effect

The bow-tie effect is a dark hourglass-shaped shadow visible across the center of elongated fancy-shape diamonds — most commonly ovals, marquise, and pears. It appears face-up under most lighting conditions as two roughly triangular dark zones meeting at the center of the stone, resembling a bow tie.

The bow tie is caused by light leakage under the observer's head. On a round brilliant the eight-fold symmetry distributes light entry and return paths so that the observer's silhouette is masked by other reflecting facets. On an elongated cut the geometry breaks the symmetry — there are pavilion zones where incoming light from above the observer leaks through the pavilion rather than reflecting back to the eye, and the leakage zones cluster at the center of the stone where the elongation puts the most stretched pavilion geometry. The leakage zones read as dark.

Every oval has some bow tie. The cutter's choice is how severe — a "soft" bow tie is barely visible under normal lighting and disappears when the stone is tilted; a "pronounced" bow tie is visible from across the room and persists under all lighting angles. Length-to-width ratio interacts with bow tie severity — longer ovals (1.5:1 and up) tend to show more pronounced bow ties because the pavilion is stretched further. Square-ish ovals (1.3:1) tend to show softer bow ties.

GIA does not grade the bow-tie effect. The GIA Diamond Grading Report lists the shape, the length-to-width ratio, and the cut grade (Excellent through Poor, where applicable), but does not flag bow tie. AGS Light Performance graded fancy shapes reflect bow-tie severity in the brightness and contrast metrics — a pronounced bow tie reduces both — but the report does not name the bow tie directly.

The buyer's rule is simple: never buy an oval, marquise, or pear without seeing a high-resolution face-up image. The face-up image shows the bow tie in detail; the GIA paper does not. Reputable retailers selling fancy elongated shapes publish 360° viewer images that show the bow tie from multiple angles; the buyer should reject any stone where the bow tie persists across viewer angles.

Marquise cuts and pear shapes follow the same rule. The geometry is slightly different — marquise has two pointed ends, pear has one — but the bow-tie zones cluster at the center of the stone in both cases. Bow tie severity is the single most important visual property to verify face-up for any elongated fancy shape; carat number, color, and clarity are all secondary to whether the bow tie is acceptable.