A knife-edge girdle has no girdle band at all: the crown and the pavilion meet in a sharp line.
In more detail
Tolkowsky's 1919 plan, our T57, has one. It saves weight but chips easily.
On a grading report
Described as Extremely Thin on the proportion diagram.
Related terms
- Girdle: The girdle is the narrow band at the widest part of a cut stone, between the crown and the pavilion. It is the edge that a setting grips.
- Girdle thickness: Girdle thickness is how thick the girdle is at its thinnest and thickest points. A report gives it as a range of words, such as "Thin to Medium".
- Tolkowsky ideal cut: The Tolkowsky ideal cut is the round brilliant that Marcel Tolkowsky calculated in his 1919 book Diamond Design. It has a 40.75° (40° 45′) pavilion, a 34.5° (34° 30′) crown and a 53% table.
- Girdle facets: Girdle facets are the small facets cut around the girdle itself, such as the 16 on the T73.