Mirror-image symmetry in a faceting design is the number of identical mirrored sections around the stone. An 8-fold mirror-image design repeats the same pair of mirrored halves eight times.
In more detail
It describes the design, not how precisely a real stone is cut. A round brilliant such as the T73 has 8-fold mirror-image symmetry.
How we measure it
Our cut pages give each design's symmetry. The Hearts & Arrows Scope averages each facet over its 16 mirror and turn copies. So a cut as designed reads 100%.
Related terms
- Symmetry: Symmetry is the report grade, from Excellent to Poor, for the exactness of a stone's outline. It also covers the shape, placement and alignment of the facets.
- Hearts and arrows symmetry: Hearts and arrows symmetry is the share of a hearts and arrows pattern where all sixteen halves match. Our Hearts & Arrows Scope gives it as a whole percent for each view.
- Symmetry (light performance): In our light-performance scores, symmetry measures how evenly the pavilion facets of each angle family are cut. It reads 100 when every facet in a family has the same angle and distance from the center.
- Index gear: An index gear is the toothed wheel on a faceting machine that sets each facet's direction around the stone. Each index is one tooth of the gear.