Convex vs Beveled Edge: Where the Rounded Grind Came From

For most of the industry’s history, hair scissors had one basic type of edge. A flat bevel ground into the blade at a fixed angle. It worked. You opened the blades, put hair between them, closed the blades, and the hair was cut.

Then a Tokyo scissor maker, Hikari, looked at a samurai sword and asked a question that had apparently not been put this way before: what if we ground a scissor blade the same way?

Hikari says that work produced the convex blade for hair scissors, and that the company obtained Japan’s first patent for a blade-angle and polishing method. Hikari was established in August 1967. Its current pages do not give the patent number, filing date or grant date, so the invention and patent claim belongs to Hikari as an attributed first-party history, not as an independently dated event.

The Beveled Edge Era

For most of that history, the standard hair-scissor edge was some variation of a beveled or knife edge. The blade is ground with a flat facet, creating a V-shaped cross section. This is the same basic geometry used in kitchen knives, garden shears, and craft scissors.

Beveled edges are simple to manufacture. You take a flat piece of steel and grind one surface at an angle until you create a cutting edge. Any competent metalworker can do it. Many sharpeners can restore it. The tools and techniques have been understood for centuries.

The limitation is what a plain beveled edge does well. When two beveled blades close on hair, they press the hair together and shear it. That suits blunt cuts and basic layering. A smooth polished bevel is a poor match for a technique that depends on the blade traveling along the strand, which is why some makers put a deliberate micro-serration on a beveled edge to hold the hair instead of letting it slide.

Bevel alone is not an absolute technique gate, though. Suitability for sliding work also depends on the polish, the edge angle, the blade line, any hollow grinding or honing, the tension, and what the maker intended the model for. One Solingen maker sells polished bevels, micro-serrated bevels, semi-convex lines and convex lines in the same catalog.

The Convex Edge: Hamaguri-ba

The Japanese name tells you exactly what the convex profile looks like in cross section: hamaguri-ba (ハマグリ刃), literally “clam shell blade.” Look at the profile of a clam shell. It curves outward from both sides, meeting at a thin edge. That is a convex blade.

The geometry was not invented from scratch. It was adapted directly from Japanese sword blade construction. Katana blades use a convex grind, called niku (肉, literally “flesh” or “meat”), to create a blade that is strong at its spine but tapers to an extremely keen edge through a smooth curve. Swordsmiths had been perfecting this geometry for 700 years before someone applied it to scissors.

How Convex Geometry Works

A beveled edge has one angle. A convex edge has a continuously changing angle, created by multiple ground planes that blend into a smooth curve.

The exact curve and angle differ by maker and model, and few makers publish them. Jaguar, for example, gives 39 degrees for its Convex Flex without saying where it is measured.

The result is a blade that slices rather than shears. When a convex blade contacts hair, it glides through with minimal resistance. The hair does not catch or fold. It separates cleanly. This is the fundamental mechanical difference that enables modern cutting techniques.

What the Rounded Profile Changes

The convex profile did not invent a separate set of techniques. It changes how much the blade resists when it travels along a strand, which is why makers position their convex models for sliding, point and texturizing work:

Slide cutting (スライドカット). Moving the partially open scissors along the hair shaft, removing length and creating texture simultaneously. The rounded outer face is what makers point to for this motion.

Point cutting (ポイントカット). Using the tips of the blades to cut into the ends of the hair, creating texture and removing weight.

Feathering and texturizing. Techniques that contact the hair at an oblique angle and depend on the hair moving across the blade rather than being held in place.

Treat that list as context, not as a rule about which edge you may use. The convex reference makes the same point from the maker side: cutting feel and technique suitability also depend on blade line, width, finish, inner relief, tension, condition, hair state and the operator. A beveled or micro-serrated construction does not necessarily pull or tear, and a smooth polished bevel is not the same tool as a serrated one. Check the model, not the label.

Beveled Edges: Not Dead, Not Pointless

It would be easy to read the above and conclude that beveled edges are obsolete. They are not.

Beveled scissors have genuine advantages:

Simpler to manufacture. Lower production costs mean beveled scissors can be offered at lower price points without cutting corners on steel quality or heat treatment.

Flat geometry to restore. Many sharpeners can restore a flat bevel on standard flat equipment. Price and turnaround still depend on the pair and the provider.

More powerful for blunt cutting. The aggressive bite of a beveled edge can actually be preferable for certain techniques. German-style scissors from Solingen traditionally use beveled edges, and many stylists trained in European techniques prefer the feel.

The German city of Solingen, Seki’s counterpart in “East Seki, West Solingen” (東の関、西のゾーリンゲン), continues to produce excellent beveled-edge scissors. Brands like Jaguar maintain that beveled edges are the right tool for certain cutting styles. They are not wrong. The choice between convex and beveled is a technique question, not a quality question.

The Hikari Connection

Hikari, a Tokyo maker established in August 1967, says it developed the convex blade for hair scissors and obtained Japan’s first patent for a blade-angle and polishing method.

That is a first-party history claim, and it is the strongest attribution available here. The patent number, filing date and grant date are not published, and no primary dataset was found for a Hikari-led adoption wave or for a convex share of the market. What the maker catalogs do establish is present-day use: Japanese and German makers alike list convex and semi-convex models. The spread of the rounded profile is best read as a retrospective label rather than a single dated event with a settled chronology.

The Sharpening Problem

Here is where the convex edge story gets complicated and expensive.

A beveled edge is defined by a single angle. Restoring it means grinding that angle back to sharpness. Straightforward.

A convex edge is defined by a designed radius, a precise curve established during manufacturing using specialized equipment and considerable skill. That radius is not arbitrary. It is engineered for specific cutting characteristics.

When a non-manufacturer sharpener takes a flat hone to a convex blade, they remove the designed radius. They flatten the curve. The scissors may feel sharp afterward, but they have lost the geometry that makes them convex. The slide-cutting ability degrades. The cutting feel changes. And here is the critical part: once the designed radius is removed by flat honing, it cannot be fully restored. The steel that formed that curve is gone.

Hikari says its convex scissors hold their geometry across repeated sharpening when Hikari does the work; the company publishes no cycle count. Each cycle removes a tiny amount of material while preserving the designed radius. Eventually the blade narrows enough that the geometry can no longer be maintained, and the scissors reach the end of their service life.

A single bad sharpening can reduce that lifespan dramatically. Hikari’s own warning about unsuitable grinding is the clearest published example, and it is a maker-specific service instruction rather than a rule that every convex brand needs the same treatment.

The Cost of Bad Sharpening

This is not snobbery. It is geometry. A convex edge is a precision-engineered surface. Treating it like a beveled edge during sharpening is like taking a sports car to a mechanic who only works on trucks. The tools look similar, but the tolerances are completely different.

Where the History Ends and the Decision Starts

This page covers how the rounded grind entered hairdressing and what it changed. It is not the buying decision. Two pages carry that:

• The edge-type comparison sets out what convex, semi-convex and beveled actually describe, and where maker terminology differs.
• Convex vs Semi-Convex vs Beveled Edge: Which Do You Need? matches the three edge types to technique, maintenance and budget.

Whoever sharpens your convex scissors, ask how they keep the designed radius. If they do not understand the question, find someone who does.

Related reading: Understand the steel types that make convex edges possible, or learn what makes Japanese scissors different in our introductory guide.