This chapter is a continued part of Chapter 3, Names of the Parts. Please read Chapter 3 |Names of Parts, before reading this section.
This chapter is about how to find the Koshi-zori or Chukani-zori. Chukan-zori is also called Torii-zori or Kyo-zori. Chukan-zori means the most curved part of the sword body comes around the middle, and for Koshi-zori, the most curved part comes lower than the center of the blade, approximately 1/3 of the lower body. Every sword looks to have its curvature around the middle part, especially when you look at photos of a sword in books. It is because those swords are placed to fit nicely in a given rectangle photo space.
The correct way to look for the curvature is to stand the Nakago (茎) vertically. In this way, you can see the location of the curvature more precisely. If the Nakago is not vertical, the curvature looks to be in every sword’s middle area. When you look at a sword, the first thing to do is to hold a sword and make sure that the Nakago stands vertically. When you look at a sword in a book, rotate (shift or slide) the book slightly so that the Nakago is perpendicular. You can see the precise location of the curvature in this way. Keep in mind; sometimes it is subtle.
Study of Japanese Sword 