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The katana is undoubtedly one of the world's most prolific and widely recognized swords. From Asia to North American, countless people collect this iconic sword or use in swordsmanship-based martial arts. This is partly because of the katana's superior quality blade. Made with high-carbon steel and differential heat treatment, it's strong yet still flexible and able to bend.
To achieve a strong blade, Japanese swordsmiths would fold the katana's blade dozens of time. Granted, it's a common myth that swordsmiths folded the katana "thousands" of times, but this isn't necessarily true. While different swordsmiths had their own unique technique, most folded the katana about 15 to 30 times. This was more than enough to achieve the desired effect, with each fold improving the blade's properties.
Overview of the Folding Process
Swordsmiths would fold the katana's blade while the metal was still red hot. After heating up the metal -- typically iron, carbon and alloys -- the swordsmiths would hammer the blade in half so that it folds traversely using a small hammer, after which he would hammer the blade in half longitudinally using a larger hammer. The swordsmith would continue this process until the desired effects were achieved. In most cases, Japanese swordsmiths would fold the katana's blade no more than 30 times.
Why the Katana's Blade Was Folded
So, why did Japanese swordsmiths feel the need to fold the katana's blade? Folding offered several benefits, one of which is metal purification. The iron sand, steel and other metals used to create traditional Japanese swords weren't devoid of impurities. Rather, they contained small, trace amounts of other metals and minerals. And when left unchecked, these impurities adversely affected swords' blade quality. To prevent this from happening, Japanese swordsmiths would fold the blade many times -- up to 30 -- so that it purified the blade.
Folding also compressed the metal together, thereby making it stronger. Each time a blade was folded, it gained strength. Over time, this bladesmithing tactic could turn an otherwise weak and frail blade into an shatter-proof blade that's perfected for the katana.
Today, Japanese swordsmiths continue to craft the katana and other traditional swords by folding the blade. It's one of the reasons that traditional Japanese swords are prized among collectors and martial arts practitioners. And while there are newer ways to produce swords, such as factory machines, they don't offer the same level of quality that's found in traditional Japanese blademsmithing tactics like folding the blade.
