Making a Katana
Historically, katana (刀) was one of the traditionally made Japanese swords (日本刀, nihontō) that were used by the samurai of ancient and feudal Japan. The katana is characterized by its distinctive appearance: a curved, single-edged blade with a circular or squared guard and long grip to accommodate two hands.
Katanas were used by samurai both in the battlefield and for practicing several martial arts, and modern martial artists still use a variety of different swords.
Katana are traditionally made from a specialized Japanese steel called tamahagane, which is created from a traditional smelting process that results in several, layered plates of steel with different carbon concentrations. This process helps remove impurities and even out the carbon content of the steel. The age of the steel plays a role in the ability to remove impurities, with older steel having a higher oxygen concentration, being more easily stretched and rid of impurities during hammering, resulting in a stronger blade. The Smith begins by folding and welding pieces of the steel several times to work out most of the differences in the steel. The resulting block of steel is then drawn out to form a billet.
Here you can see the entire process of forging this precious Samurai blade.