Anatomy of the katana

The diagram, figure by figure

The diagram on this page is drawn to scale from a blade of 71 cm nagasa (長さ) and 1.6 cm sori (反り), ordinary figures for a katana of average size. It reads as four figures.

• At the top, the complete bare blade, tang to the left and point to the right: numbers 1 to 8.
• In the middle, two enlargements. On the left the tang, with signature, file marks and notches: numbers 9 to 13. On the right the point: numbers 14 to 17.
• At the bottom, the mounted katana with the blade sheathed: numbers 18 to 32, from the hilt to the end of the scabbard.

In this diagram the blade is always drawn edge down and point to the right, the convention of parts diagrams; in a display case, by contrast, each blade is set the way it was worn.

Numbered key

1. nakago 茎 — The tang: the unpolished section hidden inside the hilt.
2. habaki 鎺 — Metal collar that grips the base of the blade and locks it into the scabbard.
3. mune 棟 — The back edge, opposite the cutting edge.
4. ha 刃 — The hardened cutting edge.
5. hamon 刃文 — The visible border between the hardened edge steel and the rest of the blade.
6. hada 肌 — The grain of the steel produced by folding and forging; also jihada (地肌).
7. hi 樋 — Lengthwise groove beside the back edge; it is usually said to lighten the blade, though no early source explains its purpose. The commonest is the bōhi (棒樋).
8. kissaki 切先 — The point section, from the yokote to the very tip.
9. nakago-jiri 茎尻 — The butt of the tang; its shape is a school trait.
10. yasurime 鑢目 — The file marks on the tang, a deliberate pattern that accompanies the signature.
11. mei 銘 — The chiselled signature, almost always on the face that looks outward when the sword is worn.
12. mekugi-ana 目釘穴 — Hole for the peg (mekugi, 目釘) that holds the blade in the hilt.
13. machi 区 — The two notches, ha-machi (刃区) and mune-machi (棟区), that divide blade from tang.
14. shinogi-ji 鎬地 — The flat band between the ridge and the back edge.
15. shinogi 鎬 — The longitudinal ridge, closer to the back edge than to the cutting edge.
16. yokote 横手 — The transverse line that marks where the kissaki begins.
17. bōshi 帽子 — The hamon inside the kissaki; also written 鋩子 (bōshi).
18. kashira 頭 — The cap that closes the end of the hilt; also tsuka-gashira (柄頭).
19. tsuka-ito 柄糸 — The silk or cotton braid wrapped around the hilt.
20. same 鮫皮 — The grainy ray skin that covers the wooden core under the braid.
21. menuki 目貫 — The pair of ornaments held against the hilt by the braid.
22. tsuka 柄 — The hilt, of wood, usually magnolia.
23. fuchi 縁 — The collar at the end of the hilt that bears against the guard.
24. seppa 切羽 — The washers that seat the guard on both faces.
25. tsuba 鐔 — The guard; also written 鍔 (tsuba).
26. koiguchi 鯉口 — The mouth of the scabbard, nearly always lined with horn.
27. kozuka 小柄 — The handle of the small utility knife carried in a pocket in the side of the scabbard.
28. kurigata 栗形 — The knob on the scabbard through which the cord passes.
29. kōgai 笄 — A slender skewer carried in a pocket on the opposite side of the scabbard.
30. sageo 下緒 — The cord that runs from the kurigata and ties the sword to the belt.
31. saya 鞘 — The scabbard, of lacquered wood.
32. kojiri 鐺 — The cap at the end of the scabbard.

The blade, from machi to kissaki

The usual cross-section of a katana is shinogi-zukuri (鎬造): a longitudinal ridge (shinogi) divides the blade into two planes, the shinogi-ji towards the back and the ji or hiraji (平地) towards the edge. Other sections exist but are exceptional on long blades: hira-zukuri (平造), with no ridge; shōbu-zukuri (菖蒲造), with a ridge but no yokote; kiriha-zukuri (切刃造), with a pronounced bevel.

The back has shapes of its own. The common one is iori-mune (庵棟), a two-sided roof; you also meet mitsu-mune (三つ棟), with three facets, and the rounded maru-mune (丸棟).

On those surfaces you read the two things that identify a blade: the hamon, the pattern of the hardening, and the hada, the grain of the folded steel. The stretch just below the yokote, the monouchi (物打), is the part that actually cuts, and it is where flaws and over-polishing are looked for first.

The point and its hardening

The kissaki is the most delicate area of a blade and the first one examined. The yokote cuts it off from the rest with a crisp line; where yokote, shinogi and ko-shinogi (小鎬) meet there is a point called mitsukado (三つ角), and how sharply it is defined says much about the polish.

By size one distinguishes ko-kissaki (小切先), chū-kissaki (中切先) and ō-kissaki (大切先), besides the short, stubby ikubi-kissaki (猪首切先) of certain Kamakura blades. The hardening inside the point is the bōshi, described by how it turns back towards the mune: ko-maru (小丸), a small round turn; ō-maru (大丸), a wide one; yakizume (焼詰), no turn at all. That return is the kaeri (返り).

A complete bōshi matters a great deal: a point whose hardening has been polished away is a serious flaw, since it cannot be restored without hardening the blade again.

The hamon: the hardening made visible

The hamon (刃文) is the visible boundary between the hardened edge and the rest of the blade, and it is the first thing looked at after the kissaki. It is neither painted nor engraved: it is the edge of the zone that hardened in the quench. Before quenching, the smith coats the blade with clay (tsuchioki, 土置き), thinner towards the edge and thicker towards the back; plunged into water, the edge cools fast and hardens into martensite, while the rest cools more slowly and stays softer. The clay moderates the width of the hardening, but the pattern does not come from the clay alone: the steel, the fire and the water all play a part, and there are quenches with no clay or with clay on only part of the blade. The whole process is in «Forging and construction».

Within that boundary two textures are told apart. Nioi (匂) is a mist of particles so fine the eye cannot separate them; nie (沸) are larger particles, visible one by one like frost. They are the same structure seen at different scales. A blade may be nioi-deki (匂出来), dominated by nioi (typical of Bizen), or nie-deki (沸出来), dominated by nie (Sōshū, Yamashiro). The line that separates the hardened zone from the rest of the blade, on the side of the back, is the habuchi (刃縁).

Inside the hamon and along its edge you see the «activity» of the hardening, the hataraki (働き): ashi (足), lines of nioi that cross the hamon towards the cutting edge; the yō (葉), a detached ashi floating inside the hamon without touching the habuchi; kinsuji (金筋), a short, bright stroke of nie; inazuma (稲妻), a kinsuji broken like a lightning bolt; and sunagashi (砂流し), strokes of nie running parallel to the boundary, like swept sand. Outside the hamon, in the ji, are chikei (地景), yubashiri (湯走り) and tobiyaki (飛焼), stray islands of hardening.

The pattern also points to school and period. Suguha (直刃) is a straight line; gunome (互の目), a row of similar semicircles; notare (湾れ), broad, gentle waves; chōji (丁子), elements with a round head and a narrow neck, like a clove bud, closely tied to early Bizen (Ichimonji, Osafune). Any irregular pattern is grouped as midareba (乱刃). A caution: the pattern does not measure quality; quality lies in the brightness and evenness of the nie and nioi. The catalogue of patterns, utsuri and the bōshi are in «The temper line up close».

Workshop practice repeats three observations. First, that the great midare and chōji of old blades were “drawn” by the steel as much as by the smith’s hand, whereas smiths today do lay out even the ashi and the yō with the clay; some even hold that certain early Bizen hardenings were done by heating only the edge, with no clay at all, although that is an unproven hypothesis. Second, that the hardening is not a surface layer but a volume: on a tantō from which 1.5 mm was ground off one side, the very active chōji on that side became much calmer, and the blade bent towards that side as it lost the stress of the hardening. That is why a subdued hamon on an old blade may be the wear of centuries of polishing rather than a style. Third, that the two sides can carry different hamon without it being a flaw: uneven clay or heat (more frequent in kotō), heavier grinding on one side, an asymmetric construction or, in the odd famous case, intent. The best known is the Konotegashiwa (児手柏) by Tegai Kanenaga, a late-Kamakura tachi with a boldly drawn midare on one side and a frayed suguha on the other. Hosokawa Yūsai named it after a poem in the Man’yōshū; according to the Meibutsuchō the name alludes to that difference between the sides, and whether the smith meant it or not is still debated.

The hada: the grain of the forged steel

Before the blade is shaped, the steel is folded and welded back onto itself many times. Folding refines it — it drives out slag and evens out the carbon — and the pattern that shows after polishing is a consequence of that work, not its aim: a striking grain does not by itself guarantee good steel. That grain is the hada (肌, also jihada, 地肌), read in the ji, the band between the shinogi and the edge. How the steel is prepared and folded is covered in «Forging and construction».

The commonest grain is itame (板目), wavy and irregular, close to the grain of a wooden board; when those waves close into concentric rings it is called mokume (杢目), like a knot in wood. Masame (柾目) is a straight grain, lines parallel to the edge, typical of Yamato and of some Osafune smiths; ayasugi (綾杉) undulates in regular, parallel curves, and is almost exclusive to the Gassan school of Dewa. Steel with no grain visible to the naked eye is called muji (無地) or mujihada. Some also note that in the Gassan school the suguha undulates into ko-gunome or notare by following the waves of the ayasugi itself, with no intention of drawing a pattern.

Grain that reads clearly and evenly is said to be tsumu (詰む), tight; when it opens up and looks coarse, arai (荒い); when the hardening of the edge is reflected inside the ji as a pale mist, that reflection is called utsuri (映り), a highly prized trait typical of Bizen. The colour and sheen of the steel itself — called jigane (地鉄) or jitetsu (地鉄) on a listing — is another thing kantei reads alongside the hada and the hamon.

The tang, the blade’s own record

The tang is never polished. Its dark, stable oxide is evidence of age, and cleaning it destroys information; in Japanese sword study it is left alone. On it you read the signature and the history of the blade.

An untouched tang is ubu (生ぶ). If the blade was shortened at the base — routine when fashion and the way of wearing it changed — the tang becomes suriage (磨上げ) or, when the cut was so large that nothing of the original tang remains, ō-suriage (大磨上げ), and the signature is often lost. Sometimes it is saved: folded over onto the other face (orikaeshi-mei, 折返銘) or cut out and inlaid as a plate (gaku-mei, 額銘). Moving the notches up without cutting the tang is machi-okuri (区送り). How to recognise each case, and what shortening does to the silhouette, is in «Shape (sugata)»; what the tang tells the appraiser, in «Kantei: how to look at a blade». In workshop practice a remade tang is filed with straight yasurime and finished with a straight-cut end, whatever the original was, so that the new work can be told from the old; and the base of an ō-suriage blade loses the flare near the machi (funbari, 踏ん張り), so the blade looks wider in the middle than at the bottom.

The mekugi-ana count: a single hole suggests one mounting and little history; three or four, several remountings or a shortening. The yasurime is a deliberate pattern — kiri (切), straight; sujikai (筋違), slanted; ō-sujikai (大筋違), steeply slanted; higaki (檜垣), crosshatched — and is compared with the smith’s own. So is the nakago-jiri: kurijiri (栗尻), rounded; iriyamagata (入山形), an asymmetric peak; kengyō (剣形), a symmetric point; ichimonji (一文字), cut straight across.

By convention a tachi signature and a katana signature sit on opposite faces of the tang, because each was worn with the edge the other way round and the signature had to face outward. An unsigned blade is mumei (無銘); one with a spurious signature, gimei (偽銘).

The mounting, piece by piece

The mounting of a later katana is the buke-zukuri (武家造), also called uchigatana mounting. It is almost never contemporary with the blade: blades outlive several mountings, and eighteenth- or nineteenth-century fittings on a sixteenth-century blade are the norm, not an anomaly.

The hilt is a wooden core split in two halves, covered with same and wrapped in tsuka-ito, with the menuki trapped under the braid and the ends closed by fuchi and kashira. The blade is held by the mekugi alone, a peg of bamboo or horn. Guard, washers and collar — tsuba, seppa, habaki — make up the assembly that seats the blade: when the work is right, the sword does not rattle.

The scabbard carries the koiguchi, the kurigata with its sageo and the kojiri, and may have side pockets (hitsu, 櫃) for the kozuka and the kōgai. When menuki, kozuka and kōgai form a matched set from one workshop they are called mitokoromono (三所物). Fittings are studied as metalwork in their own right, under the general name tōsōgu (刀装具). The parts of the scabbard, one by one, are in «The saya».

For storage out of its mounting a blade goes into a shirasaya (白鞘), a plain unlacquered wooden scabbard and hilt that do not trap moisture. If the original koshirae survives, a wooden dummy blade, the tsunagi (繋ぎ), keeps it assembled.

The measurements and how they are taken

A serious listing always gives the same quantities, and each is taken the same way. Millimetres matter: two blades of the same length but different kasane neither weigh nor handle alike.

Japanese sources and older certificates use traditional units: 1 shaku (尺) = 30.3 cm, 1 sun (寸) = 3.03 cm, 1 bu (分) = 3.03 mm. The length classes follow from them.