The image as the soul of the samurai who is wielding it, its incredible sharp edge, the long and difficult process of forging, all those points added to the reputation of the Katana as the most supreme sword ever made (刀). 

Historically, katana were one of the traditionally made Japanese swords 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.

The rise in popularity of katana amongst samurai came about due to the changing nature of close-combat warfare. The quicker draw of the sword was well suited to combat where victory depended heavily on short response times. The katana further facilitated this by being worn thrust through a belt with the sharpened edge facing up. Ideally, samurai could draw the sword and strike the enemy in a single motion. Previously, the curved tachi had been worn with the edge of the blade facing down and suspended from a belt.

The length of the katana blade varied considerably during the course of its history. In the late 14th and early 15th centuries, katana blades tended to have lengths between 70 and 73 centimetres. During the early 16th century, the average length dropped about 10 centimetres, approaching closer to 60 centimetres. By the late 16th century, the average length had increased again by about 13 centimetres  returning to approximately 73 centimetres.

Katanas are traditionally made from a specialized Japanese steel called tamahagane, which is created from a traditional smelting process that results in several, layered steels with different carbon concentrations. This process helps remove impurities and even out the carbon content of the steel. The smith begins by folding and welding pieces of high and low carbon steel several times to work out most of the impurities. The resulting block of steel is then drawn out to form a billet.

At this stage, it is only slightly curved or may have no curve at all. The gentle curvature of a katana is attained by a process of differential hardening or differential quenching: the smith coats the blade with several layers of a wet clay slurry, which is a special concoction unique to each sword maker, but generally composed of clay, water and any or none of ash, grinding stone powder, or rust. The edge of the blade is coated with a thinner layer than the sides and spine of the sword, heated, and then quenched in water, even though some sword makers use oil to quench the blade. The slurry causes only the blade’s edge to be hardened and also causes the blade to curve due to the difference in densities of the micro-structures in the steel. This process also creates the distinct line down the sides of the blade called the hamon, which is made distinct by polishing. Each hamon and each smith’s style of hamon is distinct.

After the blade is forged, it is then sent to be polished. The polishing takes between one and three weeks. The polisher uses finer and finer grains of polishing stones in a process called glazing, until the blade has a mirror finish. However, the blunt edge of the katana is often given a matte finish to emphasize the hamon.

A traditionally forged Katana is a work of art and way to delicate and expensive to just be seen as a tool to kill.