Star facets

Star facets are the eight small triangular facets on the crown of a round brilliant that sit between the table and the bezel facets. Each star points outward from the table edge, with its narrow tip touching a bezel facet and its base touching the table.

Star length — measured as a percentage of the distance from table edge to girdle — is one of the second-order proportions an AGS Light Performance grade is sensitive to. AGS Ideal-0 rounds run 50% to 60% star length. Tolkowsky's 1919 reference round had a 50% star length; modern AGS Ideal-0 rounds often run a touch longer (52% to 55%) because the slightly longer stars improve perimeter scintillation without losing center-of-stone fire.

The star length tunes the scintillation pattern at the center of the stone. Shorter stars (50%) produce a tighter, more contrast-y scintillation pattern with broader visible flashes between table and bezels; longer stars (60%) produce a finer, crushed-ice-leaning pattern with smaller individual flashes. AGS Light Performance grading reads the resulting scintillation directly via ray-trace and ASET imaging.

Star symmetry is a load-bearing input to the GIA Symmetry grade. The eight stars should be identical in size and shape; mismatched stars are flagged at Very Good or below. AGS Ideal-0 stones run star symmetry tight enough that the eight stars read as identical under 10× magnification.

Star length interacts with table percentage. A 56% table with 50% stars produces a "Tolkowsky-style" look — pronounced bezels, smaller table contribution to the visible crown. A 58% table with 55% stars produces a "modern Excellent" look — larger table, slightly longer stars to compensate. Both can earn GIA Excellent; the AGS Light Performance grade separates them on the underlying ray-trace.

The star facets do not contribute much to light return individually — they are small triangles compared to the bezels and table. Their function is to manage how light moves between the table area and the bezel area, and to create the scintillation contrast pattern at the center of the stone. A round with poor stars looks flat at the center even when its bezels and pavilion are performing correctly. The trade pays attention to stars on AGS Light Performance graded stones; on GIA Excellent rounds without an AGS supplement, star length is one of the proportions a buyer cannot easily verify from paper alone — it requires a Sarine or AGS Performance Grading Standard scan.