What is Uzumaki Hada in Japanese Katana terminology?

Uzumaki Hada or 渦巻肌 in Japanese, refers to a pattern on the surface of the ground iron (jigane) of a Japanese sword that resembles the grain of wood in a ring shape, appearing as if it is swirling in concentric circles. This is why it is called ""Uzumaki"" (swirl) ""Hada"" (skin/grain).

This pattern is seen in the works of Taikei Naotane (大慶直胤), a swordsmith from the Shinshintō period (new new sword period, 1781-1876). Naotane was known for his attempts to revive the Soshu tradition (Soshu-den), one of the five main traditions of Japanese swordsmithing, known for its bold and innovative style.

The pattern of the ground iron (jigane) plays a significant role in the aesthetics and value of a Japanese sword. It is one of the factors that sword connoisseurs look at when evaluating a sword. The Uzumaki Hada, with its unique swirling pattern, is a distinctive feature that sets the sword apart.