Convex Edge (Hamaguri-ba)
Edge typesIllustrations are navigation markers, not technical evidence. They do not establish exact geometry, material identity, finish or coating identity and properties, adjustment settings, coating colour, hair classification, tooth pattern or removal rate, mechanism, fit, diagnosis, origin, performance, or result.
Description
The convex edge (hamaguri-ba) is the sharpest grind used on professional scissors. Learn why Japanese-made convex edges excel at slide cutting and effortless closes.
Convex Edge (ハマグリ刃 - Hamaguri-ba)
Quick look
- Glide: Hollow-ground convex faces keep friction minimal, so dry sections slide without snagging.1,2
- Edge support: A narrow hone line along the hollow protects the razor-fine lip from collapsing.2,3
- Care level: Sensitive geometry chips if dropped and must be serviced by hamaguri-trained sharpeners.1,2
Why stylists pick it
Convex blades are the benchmark for buttery, quiet cutting. The continuous curve lets hair travel over the blade instead of pushing forward, which gives stylists the confidence to tackle dry detailing, channel work, and precision point cutting in a single pass.1,2 Because the interior is hollow ground, the blades meet with a gentle kiss, reducing fatigue on marathon texture sessions.2,3
Technique map
- Dry slide and channel cuts where zero drag keeps sections intact.1,2
- Precision point detailing on fringes and perimeters that need soft definition.1,2
- Texturising sweeps and feathering on fine to medium hair without leaving cut marks.2,3
Usage notes
- Keep tension just tight enough for a 45° drop test; too loose creates blade chatter on the hollow.2
- Work with light closing pressure and let the arc do the slicing - forcing the stroke dulls the edge.1
- Store the shear closed in a padded case and wipe between clients to protect the polished faces.1,2
Maintenance
- Schedule professional hamaguri sharpening and confirm the technician protects the hone line.1,2
- Request a hollow re-polish only when needed; aggressive grinding destroys the geometry.2,3
- Oil the pivot daily and brush away debris so the hollow stays clean and the close remains silent.2
Patent and resharpening lifecycle
Hikari Scissors (株式会社ヒカリ) holds patents on the application of hamaguri-ba (蛤刃) convex blade technology to professional scissors, deriving the geometry directly from traditional Japanese sword blade design. According to Hikari, each pair of scissors is designed to sustain 20 or more resharpening cycles when maintained by their factory or an authorized sharpener. However, Hikari warns that non-manufacturer sharpening can permanently destroy the designed hamaguri-ba radius, making factory service essential for preserving the intended cutting performance.4
Sources
- Hairfinder - Difference Between Convex and Beveled Shears
- Dark Stag - Convex vs. Bevelled vs. Serrated
- Japan Scissors - Hair Scissor Blade Shape and Edges Guide
- Hikari Scissors – Maintenance & Sharpening (Japanese)
- ISO 8442-5:2004 — Sharpness and Edge Retention Test for Cutlery (international standard for food-knife edge testing; the most widely recognized approach to quantifying edge sharpness, though designed for single-blade cutting rather than scissor shearing action)
See Also
Sources Reviewed
3 scoped sources behind this entry- Tertiary Hairfinder — Slide Cutting (reference)
- Secondary Japan Scissors Australia (direct sales)
- Primary 🇯🇵 Hikari Scissors — Official (manufacturer official)
Frequently Asked Questions
3 answers you can open one at a timeWhy does a convex edge feel smoother than a beveled edge during slide cutting?
The continuous curved face means hair travels over the blade rather than meeting a flat bevel that can push strands sideways. A flat bevel creates a step change in angle at the secondary edge — hair contacts that ledge, which generates drag and resistance. The convex arc removes that step entirely. Friction drops, the close is quieter, and dry sections stay intact instead of being pushed forward.
What happens to a convex edge if the wrong sharpener works on it?
Flat-hone sharpening — the standard technique most sharpeners use — removes the curved face and replaces it with a flat bevel. Once the hamaguri radius is flattened, it cannot be fully restored in the field. The scissor still cuts, but it loses slide capability and the hollow-ground interior becomes mismatched with the now-flat face. Hikari, who holds patents on the hamaguri-ba application, says each pair is designed for 20-plus resharpening cycles under factory or authorised-sharpener care — that service life evaporates after one flat-hone session.
How often does a convex edge need sharpening, and how do you know it is time?
Volume is the real driver. A busy stylist cutting 15 to 25 clients daily will typically reach the service threshold in 6 to 12 months. The practical test: close the blade on a single strand of dry hair near the tip. A sharp convex edge severs it cleanly with no pull. If the strand bends before cutting, or if the shear drags noticeably on dry slides, the edge needs attention. Waiting until the shear feels actively dull on wet blunt work means the convex geometry has already worn past its optimal profile.
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