Studying Jihada (地肌, Steel Grain)

One of the most fascinating aspects of a nihontō’s beauty lies in its jihada, the visible grain of the steel’s surface. This grain is the result of the swordsmith’s folding and forging process. During forging, the steel is folded multiple times, creating layers that appear as patterns on the blade once polished​. Depending on how the smith hammered and folded the billet, different patterns emerge. The composition of the steel (carbon content, impurities) and the smith’s technique also influence the jihada’s appearance​. A properly polished sword will reveal these patterns clearly – a good polish is essential for the jihada to be visible​

. Conversely, a blade with a dull polish, staining, or rust may show little to no grain, appearing “muji” (no pattern). Polishing can even bring out grain that was previously indiscernible​ Generally, a tight, uniform hada is a sign of a highly skilled smith, whereas a coarse or uneven hada might indicate lower skill or a tired blade​. That said, some smiths deliberately created prominent grains as part of their style, so one must distinguish intended pattern from careless forging​

Types of Jihada: There are several classic grain patterns, often linked to specific schools or regions. It’s common to see mixtures of patterns on one blade, but usually one type dominates. The main jihada types include:

  • . In the Shinto period, smiths favored very fine itame (ko-itame) that can look almost featureless (muji) at first glance. Hizen province blades have a famous super-tight itame called konuka-hada (rice grain skin), which is essentially a tiny itame so uniform it was likened to powdered rice​.
  • Mokume-hada (杢目肌) – A burl grain pattern with circular whirlpool-like figures (think of tree rings). Mokume features concentric loops and swirls quite unlike the streaks of itame. If you see obvious round “eyes” or burl patterns across the ji, that’s mokume. This hada was popular in many periods but is strongly associated with Bizen tradition, especially the Oei-Bizen school (1394–1428) whose smiths like Morimitsu and Yasumitsu produced bold mokume patterns​. A blade truly covered in mokume (rather than just a few burl spots) is distinctive – though often blades are mixed mokume and itame.
  • Masame-hada (柾目肌) – A straight-line grain that runs longitudinally (parallel to the cutting edge). Masame looks like straight parallel fibers in the steel​. This pattern is most famously a hallmark of the Yamato tradition; for instance, blades of the Hōshō school from Nara feature prominent masame throughout, which is a key kantei point for that school​. Some Shinto-era smiths also adopted masame in parts of the blade (the Sendai Kunikane line made swords with masame). It’s common to see nagare-hada, where an itame grain has been stretched in one direction, looking like running masame mixed with itame. Yamato blades and late Koto Mino blades often show masame in the upper part of the blade (shinogi-ji) while having itame/mokume in the body​. Recognizing masame, especially localized masame, can help identify those schools.
  • Ayasugi-hada (綾杉肌) – An undulating, wavy pattern often likened to a tatami mat or the grain inside a samisen (Japanese lute)​. The Gassan school is renowned for this hada (so much that ayasugi-hada is also called Gassan-hada)​. It appears as dramatic, regular waves or rolling hills in the steel. Early Gassan (Koto period) and revival Gassan smiths of the 19th century produced this distinctive pattern. Swords from Satsuma’s Naminohira school can also show a form of ayasugi-hada​. This pattern is unmistakable when visible – a beautiful example of a smith’s artistry in folding.
  • Nashiji-hada (梨子地肌) – Also called “pear-skin” grain, this is an extremely fine mokume that is tiny and densely packed (resembling the skin of a pear). Nashiji-hada is so fine it can be hard to see without excellent lighting​. It’s a hallmark of the highest-quality early Kyoto blades (Awataguchi school in late Heian/Kamakura) and some Rai school works. In the Shinto era, Osaka smiths like Tsuda Sukehiro made a similar beautiful fine grain. Hizen blades attempted to emulate this and their konuka-hada is essentially a consistent ko-itame approaching nashiji​.
  • Muji-hada (無地肌) – Not a pattern per se, but the term for when the grain is essentially invisible, giving a “plain” steel look. This can occur due to very fine forging or certain polishing methods that suppress the hada. Many highly refined Shinto blades have a muji appearance at first glance. However, modern polishes can sometimes bring out patterns in blades once thought to be muji​. If a blade truly has no visible hada, it’s often called muji-mono; some later Edo period blades and mass-produced guntō blades have this look (or an intentionally surface-polished muji).

In practice, a sword’s jihada might be described with combinations: e.g. “itame mixed with mokume, with masame in the shinogi-ji.” Advanced appraisal notes such details because they are strong clues. For example, an itame with dense ji-nie (small bright crystals in the grain) and dark chikei lines might suggest a Soshu-den work, whereas a bright, clear ko-itame with no visible pattern might suggest a 17th-century Osaka blade. Chikei (地景), which are dark, curving lines within the ji, and yubashiri (湯走り), patches of harder steel in the ji that appear like “floating” spots, are activities in the steel that seasoned collectors watch for. These features, along with a sprinkling of ji-nie (tiny hard martensite crystals in the ji), add complexity to the hada. A skilled polisher will bring out such hataraki in the jihada without making them too pronounced​

– there is a balance, as over-polishing can make grain too coarse or even polish it away.

When examining jihada, use a magnifying loupe or just very good lighting at a shallow angle. Look at how the grains flow, how they change near the edge or the ridge, and note any irregularities or ware (flaws like openings between layers). Polishing techniques can affect hada visibility: a traditional sashikomi polish will show the jihada and internal activities very clearly, whereas a hadori polish (which adds a frosted whitish outline to the hamon) may slightly mask the jihada contrast. Modern hybrid polishes sometimes use mild etching to highlight grain, but an experienced eye can tell natural hada from acid-enhanced patterns. It’s worth noting that over-polishing a sword over centuries can thin the steel so much that the outer layer (kawagane) is worn through, exposing core steel (shingane) – such a blade is called “tired” (sug疲れ)​. A tired blade may show patchy soft metal or rougher texture where core is exposed, which is a condition issue affecting collectability.

Each region had its hallmark jihada: for instance, Yamashiro tradition favors a fine mokume/itame with nie (often yielding nashiji on top pieces), Yamato tradition shows linear masame, Bizen often a visible wood grain itame with utsuri (whitish shadowy patterns) appearing, Mino blades a mix of itame and masame with patches of whitish shirake utsuri in late Muromachi, etc. With experience, a collector learns these “fingerprints” of jihada. Appreciating jihada is one of the great joys of sword collecting – under proper light, the surface of a great sword looks like flowing water or wood grain, a natural artwork created by steel and fire. Take your time to let the hada reveal itself; as the saying goes, the jihada is the skin of the sword, and a healthy, beautiful skin is the mark of a master craftsman.