What is a Convex Edge?

Hikari Scissors (株式会社ヒカリ) of Niigata Prefecture is credited with pioneering the application of hamaguri-ba to hair scissors in 1967. The company's founder drew direct inspiration from Japanese sword (日本刀) design, where the hamaguri-ba grind has been used for centuries to create blades that cut cleanly while resisting chipping. Hikari holds the first Japanese patent on the specific blade angle and sharpening method for convex-edge hair scissors. This innovation was endorsed by Vidal Sassoon and Paul Mitchell during their visits to Japan in the 1970s, establishing convex edges as the dominant premium blade profile worldwide. Before Hikari's innovation, virtually all Western hair scissors used beveled edges. The term "hamaguri" (蛤) literally means "clam" — the cross-section of the blade edge resembles a clamshell in profile. When viewed under magnification, the edge curves smoothly outward on both sides before meeting at the cutting point, with no flat facets or abrupt transitions. There are three main sub-types of convex edge used in modern scissors: full convex (smooth curve from spine to edge), semi-convex (convex near the edge with a slight flat section mid-blade), and sword-edge (asymmetric convex with a steeper curve on the inner face). Full convex is preferred for slide cutting, while sword-edge is common in dry-cutting scissors. Sharpening a convex edge requires a rotating leather or felt wheel loaded with abrasive compound, or a specialized convex honing system. Flat stones will destroy the curved geometry and convert it to a beveled edge — a common mistake made by untrained sharpeners.