Kamakura Sword Morphology: Inokubi-kissaki, Robust Body, and Nie-deki Technical Characteristics

The Three Kamakura Phases

Kamakura sword morphology divides into three phases: early (late 12th–mid 13th c., transitioning from Heian forms with widening body); middle (peak "robust" period, establishing inokubi-kissaki and broad mihaba); late (post-Mongol invasion, kissaki transitioning toward chu-kissaki).

Inokubi-kissaki: The Defining Middle-Kamakura Feature

The "boar-neck point" — short, thick, and gently rounded — is the most reliably diagnostic Kamakura feature. It represents an optimization for mounted slashing warfare: thick enough to resist breakage, curved enough for efficient cutting. Motohaba expands to 3.0–3.4 cm in mid-Kamakura, with kasane of 0.7–0.9 cm. Curvature shifts from koshi-zori toward naka-zori (peak at blade midpoint), 1.8–2.5 cm deep.

Tradition-Specific Morphology

Bizen blades show broader tip ratios (sakihaba/motohaba 65–72%), characteristic itame hada, and choji-midare hamon. Yamashiro works are slightly narrower, more refined, with ko-itame hada and suguha or ko-midare patterns. Soshu pieces show the most robust proportions with large-grain hada, deep nie activity in the hamon — the signature of Masamune's era. These regional distinctions make tradition identification possible even before a blade is signed.

Nie and Nioi: Technical Hamon Characteristics

The nie/nioi distinction — coarse glittering martensite crystals vs. fine misty glow — separates Soshu (predominantly nie-deki) from Bizen (nioi-deki) and Yamashiro (mixed). This reflects differences in quenching temperature control and clay coating techniques, making it a reliable production-center diagnostic independent of signature or style.