What is Habuchi in Japanese Katana terminology?

The term "Habuchi" (刃縁, はぶち) refers to the boundary between the Hamon (刃文: tempered pattern on the blade edge) and the Hiraji (平地: flat surface of the blade) of a Japanese sword. This is the area where various features such as Hotsure (ほつれ: frayed appearance), Uchinuke (打ちのけ: a crescent-shaped fray), and Nijuba (二重刃: double-edged) appear. These features are the result of the differential hardening process used in the creation of the sword, which involves applying clay to the blade in a specific pattern before heating and quenching. The Habuchi is a critical aspect of a sword's design, contributing to its overall aesthetic and functional characteristics.