What is Tsumu in Japanese Katana terminology?

"Tsumu" (詰む) refers to the finely detailed texture of the forged steel, known as ""Jigane"" (地鉄). This texture is the result of the swordsmith carefully selecting only the highest quality parts of the raw material and performing meticulous folding and forging. As a result, the grain of the steel becomes densely packed and visible. While this fine texture is similar to the ""Kagami-hada"" (鏡肌) seen in the Shinshintou period, it is fundamentally different from the monotonous Kagami-hada, which results from using homogeneous materials.

This term reflects the high level of skill and attention to detail required in sword making. The selection of high-quality materials and the meticulous folding and forging process result in a densely packed grain, which is a testament to the quality of the sword. The comparison with the Kagami-hada of the Shinshintou period underscores the diversity of styles and techniques in sword making."