What is Koshiba in Japanese Katana terminology?
Koshiba refers to a type of blade pattern (Hamon) in Japanese swords. It is characterized by a deep and large pattern of tempered steel on the upper part of the "刃区" (Hamachi), which is the boundary between the blade and the tang. This pattern is often seen in the works of swordsmiths such as "長光" (Nagamitsu) from Bizen Province and "村正" (Muramasa). In particular, those seen in the swords from Mino Province during the Muromachi period are specifically referred to as "美濃腰刃" (Mino Koshiba).