What Is Fukura? ふくら — The Curve of a Sword's Tip Explained
The fukura (ふくら) is the curvature of the cutting edge within the tip of a Japanese sword — the arc of the edge across the kissaki, from the yokote line down to the very point. It describes how full or how lean that curve is, and it is both a design trait chosen by the smith and a condition detail scrutinised in appraisal. A well-shaped fukura is a mark of a healthy, correctly polished tip; a lost or flattened one is a warning sign.
To a collector, the fukura is one of the most sensitive reading points on the whole blade. The kissaki is the hardest area to forge, temper and repair, so the state of the fukura reveals a great deal about a blade's originality, its polishing history, and the skill of the smith who shaped it.
The two states of the fukura
The edge curve in the tip is classed by how much it bulges:
- Fukura-tsuku (ふくらつく) — a full, rounded, generous edge curve in the kissaki. It is considered healthy and robust, and is typical of Bizen work and of many blades in good original condition.
- Fukura-kareru (ふくら枯れる) — a thin, lean, "withered" edge curve with little roundness. It can be an original stylistic feature — the Soshu master Masamune and the Sadamune line are known for a lean fukura — but it can also be the result of repeated polishing that has eroded the tip.
Because the same appearance can be either intentional or damage, the fukura must be read together with the rest of the tip: the length and turn-back of the boshi, the crispness of the yokote line, and the overall proportion of the kissaki.
How to read the fukura in kantei
A full fukura-tsuku edge that matches a broad, well-proportioned kissaki with a healthy boshi is the picture of an original, unmolested tip. A lean fukura-kareru edge is scrutinised carefully: if the boshi is short and the yokote sits high and cramped, the tip has likely been reshaped or over-polished and has lost steel. If the lean edge is paired with a long, elegant boshi and correct proportions, it is more likely an original Soshu-style trait.
This is why the fukura is a money-intent detail. A kissaki that has been repaired after a chip — a common failure point in use — often shows a compromised fukura, a shortened boshi, or a re-cut yokote. Such a tip dramatically lowers a blade's value and, in serious cases, means the hardened edge no longer reaches the point at all.
Why the fukura matters to buyers
The tip is the single most important area for condition, and the fukura is its clearest indicator. Before buying, a collector examines the fukura under raking light to confirm the edge curve is even and uninterrupted, that no hagire (fatal edge cracks) run through it, and that the boshi turns back properly. A blade whose fukura has been ground away to remove a chip is functionally and financially diminished, even if the rest of the sword is fine.
In short: fukura-tsuku on a blade with a matching healthy tip is what buyers want to see; fukura-kareru demands you confirm whether it is the smith's intent or the polisher's loss.
Frequently asked questions
What does fukura mean on a Japanese sword?
Fukura (ふくら) is the curvature of the cutting edge inside the kissaki, the arc of the edge from the yokote line down to the point. It is both a design choice and a condition detail, and it is one of the most closely read features when appraising a blade's tip.
What is the difference between fukura-tsuku and fukura-kareru?
Fukura-tsuku is a full, rounded, healthy edge curve in the tip, typical of Bizen work. Fukura-kareru is a thin, "withered" edge curve; it can be an original Soshu trait as in Masamune, or the result of over-polishing that has eroded the tip.
Why is a withered fukura a concern when buying a sword?
A lean fukura can mean the tip was reshaped after a chip or lost steel to repeated polishing, which lowers value. You must read it alongside the boshi and yokote: a lean edge with a short boshi and cramped yokote signals damage, not intent.