English archers had their longbows, Old West sheriffs had their six-guns, but samurai warriors had the most fearsome weapon of all: the razor-sharp, unsurpassed technology of the katana, or samurai sword. In this program, NOVA probes the centuries-old secrets that went into forging what many consider the perfect blade.
The beauty and lethality of the curved steel blade became identified with the distinctive culture of those who wielded it so expertly: the samurai warriors of medieval Japan, celebrated in countless Japanese woodcuts, prints, and films. Fifteen traditional Japanese craftsmen spent nearly six months creating the sword that NOVA follows through production, from smelting the ore to forging the steel to sharpening the blade to a keen edge, capable of slicing through a row of warriors at one swoop—although NOVA does not put the super-weapon to this ultimate test. (See a slide show of the process.)
Not that samurai sword fighting has died out—far from it. The program also traces the schooling of a modern-day devotee of samurai combat: Midori Tanaka, a receptionist for a Japanese electronics firm by day and a blade buff by night. For Tanaka it's a family tradition, since her father, Fumon Tanaka, is a grand master swordsman.
Father and daughter show their mutual respect with a breathtaking test of skill. Midori draws a bow, aiming an arrow directly at her father's heart. His only protection is his sword. When she releases the string, he slices the speeding arrow in half, inches from its target.
Japanese sword-making developed centuries ago, before electron microscopy, mass spectrometry, and other tools of modern materials analysis enabled scientists to understand exactly why the swords are as good as they are. Professor Michael Notis of Lehigh University, an expert on samurai swords, sheds light on the principles that underlie the weapons' strength, resilience, beauty, and distinctive shape. (See an interview on metal's properties with Notis's colleague Rick Vinci.)
For example, during smelting, iron-ore sand is heated with charcoal, which provides a source of carbon that alloys with the iron to create steel. Ancient craftsmen deliberately stopped just short of a uniform liquid state for the white-hot steel, which resulted in a product with varying amounts of carbon throughout. The harder high-carbon steel was forged into the sword's edge, which had to be hard and sharp, while the more resilient low-carbon steel was used as the core of the weapon to produce a blade resistant to breaking during combat.
This sandwich of two different types of steel contracted at different rates during rapid cooling, or quenching, which caused the blade to warp lengthwise, giving it its distinctive curve that proved so deadly when wielded in a slashing arc. "The unique aspect of the Japanese sword is that the craftsmen were able to put the right materials in the right place to get optimum properties for the entire object," Notis tells NOVA.
Without access to the insights of modern science, Japanese craftsmen a millennium ago worked out an exacting method that is still followed by a devoted few and that produces the Stradivarius of swords.