The octagonal step cut is a faceting arrangement applied to an eight-sided gemstone outline, featuring concentric rows of rectangular facets parallel to the girdle on both crown and pavilion. It is, in essence, the emerald cut applied to an octagon, and the two terms are often used interchangeably in the trade. The cut combines the geometric formality of the step cut with the chamfered-corner safety of the octagonal outline, producing one of the most enduring and recognisable styles in coloured-stone cutting.

Geometry

The octagonal step cut typically has an eight-sided girdle outline, with four longer sides and four shorter chamfered corners. The crown carries a flat table facet at the top, surrounded by one or more rows of step facets descending toward the girdle. The pavilion mirrors this arrangement with rows of step facets descending toward the culet (or, in stones with no culet, meeting at a single line or keel).

The number of step rows on the crown and pavilion varies with the depth of the stone and the cutter's preference. Shallow stones may have only one or two step rows; deeper stones may have three or four. The table is sized in proportion to the girdle, typically occupying 50 to 65 percent of the girdle width.

Optical properties

Step-cut faceting produces broad, mirror-like flashes of light rather than the small scintillating flashes of brilliant cuts. The optical signature of a fine step cut is the hall-of-mirrors effect, where each step reflects an image of the others, producing a luminous, layered appearance through the table. The open table also makes the cut excellent for displaying colour, which is why it is the preferred cut for fine emeralds, sapphires, aquamarines, and tourmalines where colour is the primary value driver.

Step cuts are less forgiving than brilliants of optical imperfections. Windows (light leakage through the pavilion), extinction (dark central areas), and visible inclusions are more readily seen through the open table. A well-proportioned octagonal step cut requires careful angle work on the pavilion to maintain light return; the cutter typically targets pavilion angles in the 39–43 degree range depending on the material's refractive index.

Practical advantages

The chamfered corners of the octagonal step cut serve as protection for vulnerable points. Sharp corners on a rectangular outline concentrate stress and are prone to chipping during setting and wear; the chamfers distribute stress more evenly. For brittle materials including emerald and tourmaline, the octagonal outline is materially safer than the rectangular alternative.

The cut is well-suited to the elongate prismatic crystal habits of beryl, tourmaline, and topaz, allowing the cutter to maximise yield from rough that has natural rectangular tendencies. The trade has accordingly standardised on the octagonal step cut for these species, with calibrated sizes available widely for setting in commercial mountings.

GIA recognition and grading

GIA recognises the octagonal step cut as a distinct shape category in coloured-stone grading reports, with shape designations including emerald cut, octagon, and step cut appearing in various combinations depending on outline and faceting. For diamond grading, the closely related emerald cut appears as a separate shape category, and the Asscher cut (a square octagonal step cut with elaborated facets) has its own category as well.

Further reading

• GIA Gems & Gemology — coloured-stone cutting
• International Gem Society — step cuts
• Lapidary Journal — faceting reference