Hairdressing Scissor Blade Geometry: Convex, Bevel & Semi-Convex
Written by Matt Grumley, a hairdresser and scissorsmith. Founder of ShearGenius, est. 2007.
Steel sets the ceiling. Geometry decides how close to that ceiling the scissor actually gets. The same ATS-314 billet can be ground into a scissor that slide-cuts like silk or one that folds hair like a wet tea-towel — the difference is the blade profile.
The Three Edges That Matter
Convex (Hamaguri-ba)
The Japanese hollow-ground edge. The inside of each blade is slightly concave, and the cutting edge itself is a smooth convex curve meeting at 20-30°. Razor sharp, slices on contact, and absolutely required for slide cutting, point cutting and any modern dry-cutting technique. Every ShearGenius scissor ships with a true convex edge, hand-finished on Japanese water stones.
Semi-Convex
A compromise grind: convex on the outside, bevelled on the inside. Cheaper to manufacture and more forgiving of rough handling, but will not slide cut cleanly. Commonly found on mid-tier European and Korean scissors.
Bevel Edge
The traditional flat-ground edge at 40-50°. Durable, easy to sharpen on a basic machine, but push-cuts rather than slices. You can feel the hair being crushed rather than parted. Fine for blunt-cutting coarse hair; wrong for any modern technique.
Which Geometry for Which Technique
- Slide cutting: Convex only. Bevel and semi-convex will drag and snag.
- Point cutting: Convex preferred. The tip must be razor sharp and unchipped.
- Blunt cutting wet hair: Any of the three will work; convex gives the cleanest line.
- Texturising with a teethed blade: The cutting blade should still be convex — the teeth handle the weight removal.
How to Spot a True Convex Edge
Hold the scissor open under a bright light and sight down the ride line. A true convex edge shows a smooth, continuous curve with no flat facets. A bevel edge shows a distinct angular line. A semi-convex looks convex from the outside only — the inside face is flat.