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

No.	Term	What it is
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	Groove cut beside the back edge to lighten the blade; the commonest is the bō-hi (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.
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.
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 is the line that separates the hardened edge from the rest of the blade, and it is the first thing examined after the kissaki. It is not painted or etched on: it comes from coating the blade before quenching with a layer of clay left thinner toward the edge and thicker toward the back (tsuchioki, 土置き), so the edge cools fast and hardens into martensite while the rest cools slowly and stays softer. The border between the two steels is the hamon.

Two textures show up within that border. Nioi (匂) is a mist of crystals so fine the eye blends them into a bright, continuous line; nie (沸) are larger martensite crystals, visible one by one like frost on the steel. A blade can be nioi-deki, predominantly nioi (typical of Bizen), or nie-deki, predominantly nie (typical of Sōshū or Yamashiro). The upper edge of the hamon, toward the ha, is the habuchi (刃縁); loose nie crystals that have broken away from that border also show inside the ji, named by their shape kinsuji (gold threads), sunagashi (drifted sand) or ashi (legs reaching down from the habuchi to the edge).

The outline of the hamon also marks school and period. Suguha (直刃) is a straight line, with no undulation; gunome (互の目) forms a run of regular arcs, like rounded sawteeth; notare (のたれ) undulates in gentle, irregular curves; chōji (丁子) gathers into clusters recalling cloves, closely tied to early Bizen work (Ichimonji, Osafune). Any irregular pattern falls under the general name midare (乱れ). Inside the kissaki, the same hardening is called the bōshi, covered in the previous section.

The hada: the grain of the forged steel

The steel of a katana does not leave the forge uniform: the smith folds and welds the bar onto itself again and again, and each fold leaves a visible line once the blade is polished. That grain is the hada (肌, also jihada, 地肌), read on the ji, the band between the shinogi and the edge.

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.

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 fashions in length changed — the tang becomes suriage (磨上げ) or, when the cut was drastic, ō-suriage (大磨上げ), and the signature is often lost. Sometimes it is saved: the original signature is folded over (orikaeshi-mei, 折返銘) or cut out and re-inset as a plate (gaku-mei, 額銘). Moving the notches without removing steel is machi-okuri (区送り).

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-ana, 櫃穴) 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).

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.

Measurement	How it is taken
nagasa 長さ	In a straight line from the mune-machi to the tip, not along the curve.
sori 反り	Greatest distance between the back and the chord joining mune-machi and tip.
motohaba 元幅	Width of the blade at the machi.
sakihaba 先幅	Width at the yokote.
motokasane 元重ね	Thickness of the back at the machi.
sakikasane 先重ね	Thickness of the back at the yokote.
nakago-nagasa 茎長さ	Length of the tang, machi to nakago-jiri.
Weight	Of the blade alone, with or without habaki; a listing should say which.

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.

Type	Nagasa
katana or daitō	2 shaku or more, that is from 60.6 cm
wakizashi	Between 1 and 2 shaku: 30.3 to 60.6 cm
tantō	Under 1 shaku: less than 30.3 cm