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.
If you're reading that list and not sure which of those techniques you actually lean on day to day, that's exactly what a fitting is for. Tell me how you cut and I'll tell you which edge you need — book a free fitting before you spend a dollar. It's easier to match a scissor to your hands than to retrain your hands to a scissor.
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.
One more thing worth knowing: geometry isn't just about how the scissor cuts new — it's about how it gets sharpened. A convex edge put on a basic bench grinder comes back a bevel, and getting a true convex back after that is a much bigger job than keeping it right in the first place. It's why we hand-sharpen convex edges properly — it's a paid service, $70 to $80 a scissor, and after 100,000+ scissors across the bench, the wear on your edge usually tells me how you cut before you do.