The Four Eras of Japanese Swords—Dating and Authentication Guide: Reading Age Through Form, Steel, Hamon, and Nakago

The history of Japanese swords spans approximately 1200 years. When organizing this extensive history, four essential time period classifications are indispensable: "jokotō (ancient swords)," "kotō (old swords)," "shintō (new swords)," and "shinshintō (newer swords)." These are far more than mere chronological divisions; the form, forging techniques, purposes, and cultural backgrounds of blades differ fundamentally across each era, making them essential foundational knowledge for appraisal, collection, and research alike. This article compares and explains the characteristics of each era from three perspectives: morphological, technical history, and appraisal practice.

Jokotō (Ancient Swords) — The Straight Blade Era Before Curvature

Jokotō generally refers to swords made before the early Heian period (late 9th century). In a broader sense, it also includes straight swords (chokutō), iron swords, and ring-pommel swords (kantōtachi) from the Kofun through Nara periods.

The most important morphological characteristic is the "absence or extreme scarcity of curvature (sori)." Made based on iron-forging techniques transmitted from the continent (China and Korea), the cross-section typically features edge-ridge construction (shinogi-zukuri) or flat construction (hiradzukuri), resulting in straightforward blade profiles. The "hair-plucking-pattern sword (kenuki-gata-tachi)" exemplifies jokotō, distinguished by its unique perforated pattern in the nakago (tang) resembling a hair plucking tool.

Forging techniques were still underdeveloped, and the number of folding-and-hammering cycles remained limited. Tamahagane (jewel steel) had not yet been established; instead, direct forging of iron sand resembled "continental-style production." As a result, compared to later Japanese swords, the jigane (base steel) lacked uniformity, and hamon (temper line) typically showed straightforward straight edges.

From an appraisal standpoint, extant jokotō are extremely rare, with most housed in shrines or museums. Those bearing a mei (signature) are even scarcer, and distinguishing them from contemporary Chinese or Korean blades can be difficult.

Kotō (Old Swords) — The Golden Age of Japanese Swords (Late Heian–Keicho)

Kotō refers to swords made from approximately the late Heian period (10th–11th centuries) through the Keicho era (1596–1614). This time period classification is the broadest, encompassing the turbulent ages of Kamakura, Northern and Southern Courts, Muromachi, and Sengoku.

Morphologically, this era saw the establishment and development of "curved Japanese swords (swords with sori)." Characteristics vary by period.

From late Heian through early Kamakura, "hip curvature (koshi-zori)" — curvature concentrated near the blade's base — dominated, suited to draw-cutting in cavalry combat. Blades were slender and long, with many small kissaki (points). Representative production centers included Awataguchi near Yamashiro (Kyoto region) and Osafune in Bizen (Okayama).

In the Northern and Southern Courts period (14th century), suddenly "great swords (ōtachi) and field swords (notachi)" surged in popularity. Massive blades exceeding 90 cm in edge length were produced in quantity, many later re-worked through suriage (shortening of the tang) to create uchigatana (practical swords).

From the Muromachi through Sengoku periods, practical "uchigatana (worn swords)" became standard; blades featured greater width with less variation in body width, and chūkissaki (medium points) became more common. The Five Transmission Schools (Yamashiro, Yamato, Bizen, Soshu, and Mino) were established, with each region developing distinctive characteristics.

The technical apex of kotō came through Masamune of the Soshu transmission, who perfected "strong nie in base steel combined with exuberant midare (random) hamon." Subsequently, this became the technical standard that later swordsmiths aspired to.

Shintō (New Swords) — The Edo Peace and Morphological Transformation (Keicho–Early Bakumatsu)

Shintō is conventionally defined as spanning from around Keicho (1596) through around Meiwa 1 (1764). Marking the end of the Sengoku period and the establishment of the Edo shogunate, swords transitioned in purpose from "practical weapons" to "formal attire and symbols of samurai status."

A notable morphological change was the reduction in edge length and the thinning of the mine (ridge thickness). In an era of peace, oversized swords like ōtachi became unnecessary, and approximately 70 cm uchigatana became standardized. "The difference between blade width at hilt and tip is small" typifies shintō form, and "rounded cross-sections develop" is also characteristic.

Osaka emerged as a major production center, with swordsmiths like Sukehiro and Shinkai pioneering "Osaka shintō." The "wave-turbulence hamon (tōranba)" — a wave-like form of grand midare — symbolized Osaka shintō, reflecting the pursuit of aesthetic value for viewing and formal purposes.

In Edo, Naganosone Okisato Kotetsu gained renown for "practical cutting performance," while regional domains like Mito and Satsuma established their own distinctive styles through officially patronized swordsmiths.

From an appraisal perspective, shintō survive in far greater numbers than kotō, and examples bearing certificates (from tokubetsu-hozon to important sword status) are more readily available. However, works from the early Keicho period — when characteristics from both end-period kotō and early-period shintō intermix — require specialized expertise for accurate attribution.

Shinshintō (Newer Swords) — The Age of Archaism and Technical Innovation (Tenmei–Early Meiji)

Shinshintō spans from around Meiwa (1764) through the early Meiji period (circa 1876, around the Haitorei edict). This was an era when a revivalist movement championing "return to kotō" swept the sword world.

The ideology epitomizing this era appears in works such as Suishinshi Masahide's "Kengō Hiden-shi" and "Tōken Ben-gi." Arguing that "the soft steel and flamboyant hamon of shintō contradict the spirit of kotō," he advocated for revival of Bizen and Soshu transmissions.

Morphologically, imitations of kotō forms — particularly the "boar-neck kissaki (inoko-kubi-kissaki)" and "small kissaki" of Kamakura kotō — increased. Taikei Naotane attempted restoration of the Bizen transmission, while Minamoto Kiyomaro perfected the Soshu transmission's strong-nie, chaotic hamon.

However, this was not complete archaism; "shinshintō's own individuality" emerged. During the bakumatsu period, as royalist-exclusionist sentiment intensified, demand for "practical swords" resurged, and many blades used by the Shinsengumi and political activists were shinshintō. Typical lengths were 70–80 cm, and hamon forms — including straight edges and mutual-eye midare — varied widely, with temporal tensions reflected in the blades' proportions.

Morphological Comparison Across Four Eras: Practical Appraisal Points

Effective comparison points for period determination are summarized below.

Conclusion — Four-Era Classification as the Starting Point for Appraisal

The four time period classifications — jokotō, kotō, shintō, and shinshintō — form the foundational map for systematically understanding Japanese swords. Though all are "Japanese swords," their form, base steel, hamon, and tang condition each reflect their respective era deeply.

In collection and appreciation, the first step of evaluation is determining "to which era classification this sword belongs." Changing eras changes comparison criteria; the same "midare hamon" in kotō's choji and shintō's tōranba carry entirely different technical backgrounds and evaluative frameworks.

Understanding the four era classifications is the ability to read masterwork blades correctly, and the first step toward profound respect for Japanese sword culture.