Jihada Typology: How Itame, Masame, Mokume, and Ayasugi Steel Textures Are Formed

Jihada — The Steel Layers Born from Folding and Forging

The "ji (地)" of a Japanese sword refers to the surface structure of the steel on the flat face of the blade (hiraji). Through the process of repeated "oriakaeshi tanren (折り返し鍛錬)" — folding and reforging the iron many times — layers of steel accumulate thinly and stack together, and after polishing, a wood grain–like pattern appears. This is jihada, also called tanneihada.

In typical oriakaeshi tanren, about 15 to 17 folds are made, creating steel sheets with 2^15 (approximately 32,000) to 2^17 (approximately 130,000) layers. Depending on the direction, temperature, and striking method of each fold, the flow of the layers changes, and different jihada patterns emerge.

Itame (板目) — The Most Common Jihada

Itame resembles the wood grain seen when splitting a wooden board lengthwise, and it is the most widely seen jihada pattern in Japanese swords. When folding is repeated in a single direction (mainly from the blade edge toward the spine), the layers align with their flow direction, producing itame-like grain.

Itame also includes sub-categories such as "ōitame (大板目)," "koitame (小板目)," and "nagare itame (流れ板目)." Ōitame displays prominent wood grain–like flows and has striking visual presence, but some appraisers evaluate it as "rough forging." Koitame has fine, uniform flows and is commonly seen in Bizen-den swords.

Nagare itame has the flow strongly unified in a single direction, appearing like a water current. It is scattered among Yamashiro-den and Yamato-den swords and indicates a unified forging direction.

Masame (柾目) — The Straight Beauty Born from Yamato-den

Masame is a linear jihada that runs parallel in the vertical direction, resembling the straight wood grain seen when wood is rift-sawn lengthwise. In oriakaeshi tanren, the basic principle is one-directional forging from the spine toward the blade edge, and by striking in the same direction with each fold, the layers align vertically.

This jihada was frequently used by sword smiths of the Yamato-den (Nara) tradition, with particularly characteristic masame appearing in swords of the Hōshō and Tegai schools. Masame possesses strong linearity, and it is said that the "earnestness" of the forging most directly appears in this jihada among all patterns. If even one line is warped, the disturbance in striking becomes visible; therefore, maintaining beautifully aligned masame requires strict control of the folding direction.

Even among modern sword smiths, many attempt to reproduce masame, but perfectly aligned masame is difficult to achieve, and itame is often partially mixed in. When examined under a microscope, the masame of Yamato-den swords from the Koto period displays an oddly orderly arrangement of each individual line, and even modern scientific analysis has not yet achieved complete clarification of the reproduction mechanism.

Mokume (杢目) — The Burled Jihada Born from Swirling Forging

Mokume is a swirling jihada resembling the burls or wood grain patterns seen in tree cross-sections, created by intentionally varying the direction of oriakaeshi tanren. By changing the folding direction 90 degrees during itame forging or incorporating rotational forging, the layers become intricately intertwined and appear swirl-like.

Mokume is frequently seen in Soshu-den swords, and particularly in mid-period Soshu-den swords where "mokume kitae (杢目鍛え)" was intentionally performed, the complexity of the jihada and the richness of jibye (地沸え) unite to create a distinctive landscape.

For mokume to appear beautifully, the selection of whetstones during the polishing stage is crucial. When carefully finished with "jito (地砥)," fine-grained whetstones specifically for jihada polishing, the three-dimensional relief of the swirling pattern stands out. It can be said that the beauty of jihada is completed only through collaborative work between the togishi (polisher) and the sword smith.

Ayasugiume (綾杉目) — The Secret Forging of the Gassan School

Ayasugiume is a distinctive jihada appearing as if the needles of a cedar tree are arranged in regular order, born from the unique forging method called "ayasugi kitae (綾杉鍛え)," said to be passed down only by the Gassan lineage to the present day.

Gassan Sadaichi restored and transmitted this technique from the Meiji through Showa periods, and the 2nd Gassan Sadaichi (Living National Treasure) established the technique. During oriakaeshi tanren, iron is folded in a zigzag pattern (alternately diagonal), and by repeating a special pattern of forging directions, a regular fine-line pattern appears alternating left and right like cedar needles.

Ayasugiume remains mysterious even to jihada researchers. Due to technical transmission through oral tradition within the Gassan lineage, scientific analysis from outside is difficult, and a complete reproduction model as metal microstructure remains partially unexplained. In the modern era, Gassan Sadatoshi (equivalent to 3rd generation) carries on this technique, but the successor question is serious, and it is said the technique of ayasugiume stands at the brink of extinction.

The Correlation Between Jihada and Hamon — Forging Design Philosophy

Jihada and hamon are not independent techniques but are one as a unified forging design philosophy. For Bizen-den to achieve "itame with choji," the carbon concentration distribution of the steel, the number of folds, and the clay arrangement are designed as a consistent total design. This is why when modern sword smiths study the style of a particular school, they research jihada and hamon as a set.