Tameshigiri (試し斬り, tameshi giri) is a cutting test performed with Japanese swords, often with a katana. In medieval Japan, sword testers, occasionally including samurai, would test new blades on the bodies of executed individuals or even on living subjects.
Up to three bodies could be used simultaneously. The results of these cutting tests were recorded on the tang (nakago) of the sword and are often found on blades by the swordsmith Kotetsu (長曽祢虎徹, Nagasone Kotetsu, 1600–1673). Samurai would also conduct these tests on condemned criminals who were still alive.
Today, specially wrapped mats known as tatami-omote made from igusa grass (Juncus effusus) are used, which are soaked in water for 12 hours before the cut and then dried for approximately 4 hours, or green bamboo stalks with diameters ranging from about 5.7 cm to 12.7 cm.
Various cuts are practiced with a sharp sword, including diagonal, horizontal, vertical, one-handed, or two-handed cuts. The quality of the blade and the cutting technique of the practitioner can be assessed based on the cut surface.
It is important that the angle of the blade precisely matches the angle of the cut to prevent the sword from getting stuck, which would impede a clean cut and could even result in bending or, rarely, breaking of the blade.
Tameshigiri is not directly related to Iaido, but some practitioners of Iaido practice it to test their cutting technique. It was also an important component of European historical swordsmanship, regularly practiced to improve blade control, posture, and the feel for the weapon.
Each cutting test carries risks for the blade and can potentially damage the polish. Therefore, particularly valuable or historically significant blades were often excluded from these tests, such as blades by renowned smiths like Masamune and Muramasa.