What is Hizukuri in Japanese Katana terminology?

"Hizukuri" (火造り) refers to the process of heating the sword blade until it turns red and becomes soft, then hammering it into the desired shape. This involves the swordsmith using a small hammer to thin out the blade side, slightly thin out the spine side, and establish the ridge line (Shinogi-suj, 鎬筋), thereby finishing the shape of the sword. During this process, the swordsmith visualizes how the ridge, spine, and Yokote (the line that separates the blade from the tip) will turn out. This is a critical step in sword-making, as it determines the final shape and structure of the sword.