The traditional practice of folding a katana blade multiple times during the forging process had several purposes and benefits:
- Refining the Steel: Folding helped to refine the steel and improve its overall quality. Each fold allowed the swordsmith to remove impurities, distribute carbon more evenly, and create a more homogenous steel composition.
- Eliminating Welding Imperfections: During the forging process, different pieces of steel were joined through forge welding to form the blade. Folding helped to ensure a strong and secure bond between the layers, removing any potential imperfections or weak points in the welds.
- Enhancing Structural Integrity: The repeated folding and layering created a laminated or layered structure within the blade. This structure provided strength, durability, and resistance to deformation during combat. The layered construction also helped to prevent the blade from breaking or shattering.
- Developing Distinctive Patterns: Folding and layering the steel resulted in the formation of distinct grain patterns known as "hada." These patterns were highly prized for their aesthetic appeal and uniqueness, and they added to the visual allure and artistic value of the katana.
- Achieving Consistency: Folding contributed to achieving a consistent distribution of carbon content throughout the blade. This allowed for a uniform hardness and edge retention, which were essential for the katana's cutting ability.
While the exact number of folds varied, it is a misconception that katanas were folded hundreds or thousands of times. Historical records and analysis of authentic katanas suggest that they were typically folded between 8 to 16 times. The folding process was carried out with precision and care to achieve the desired balance of properties in the blade.
It's important to note that modern manufacturing techniques and advances in steel production have made it possible to create high-quality katanas without extensive folding. Some modern swordsmiths may choose to incorporate folding techniques as a nod to tradition or for artistic purposes, even if the practical benefits are minimal.
