Forging a sword was a sacred act according to shinto beliefs. The swordsmith prepared, cleaned and dressed himself with special care before forging a sword, each phase of manufacture being prone to failure. Tempering the blade was the most sacred phase, with water cooling taking a matter of seconds. The result was a tempering stripe, hamon (blade design), a shiny groove along the edge of the blade, running from top to bottom. Finally, the blade was sharpened and polished. The centre of the blade was softer and more flexible than the surface, which was very hard and sharp for stabbing. Professional testers evaluated the quality of new swords and their penetration, and the steadiness of the wielder's hand was tested by piercing helmets, various parts of armour or the corpses of beheaded criminals (tameshigiri).
