1. The Folding of Katana Blades Thousands of Times is a Myth
Katana makers solved the dilemma of a sword that had to be both sharp and hard-edged via the use of four metal bars. A soft iron bar to guard against breakage, sandwiched by two hard iron bars to prevent bending, and rounded off with a steel bar to take the cutting edge. The result was a sword that had a hard enough blade, and a sharp cutting edge. However, contra many a WWII tall tale, no katana was ever hard enough, or sharp enough, to cut through machine gun barrels. The four metal bars of which katanas were made were heated at high temperatures, then hammered into a long bar that would become the blade.
Contrary to myth, katana blades were not folded thousands of times. So many folds would be counterproductive, and render the steel useless for a sword. Instead, katana blades were folded between eight to sixteen times. When the sword was sharpened, the steel took a razor-sharp edge, while the softer iron kept the blade from breaking. Well-crafted katanas became prized heirlooms, passed down generations of samurai families for centuries. Magnificent specimens of centuries-old katanas can be seen in the Tokugawa Art Museum in Nagoya, Japan.
Where Did We Find This Stuff? Some Sources and Further Reading