Making a Samurai Sword

  • Posted 12.08.16
  • NOVA

Using accidental chemistry and sheer brute force, swordsmiths in 12th century Japan took crude pig iron and turned it into a deadly weapon—the Samurai sword.

Running Time: 02:32


In the 12th century, master craftsmen in Japan transformed pig iron—a weak metal riddled with impurities—into a material strong enough to help shape our world.

Over centuries, Iron forging was turned from a skill into an art form.

Using technology that wouldn’t reach Europe for hundreds of years, Japanese swordsmiths created the samurai swords, famous for their unparalleled strength.

This deadly weapon started life as an impure lump of crude pig iron.

So how do you transform it into the amazing metal of the samurai?

Rick Vinci, a metals expert from Lehigh University reveals that the secret is simply brute force…

They would heat it and hammer it, and after they had done so they would fold it over upon itself and heat it and hammer it again, and they would do this many, many times. And every time they would go through this hammering process they would drive out many of the impurities.

With every blow the impurities are smashed away. It takes hundreds of blows but every time it is hit this metal becomes purer and purer.

And unbeknownst to them they would also be altering the carbon content.

Carbon is the most important impurity in iron.

Too much and the iron will be brittle, not enough and it will be soft.

But by smashing out just enough carbon the swordsmiths were left with a metal with extraordinary strength and unmatched flexibility.

The end product was really good material, they could make swords out of it that would hold a sharp edge, that would survive use on the battlefield without shattering.

What the swordsmiths had created was a new kind of metal…

A new alloy—that to this day is the strongest, most useful alloy we’ve ever discovered—steel.



Series Director
Kate Dart
Benedict Jackson
Director of Photography
Piers Leigh
Ari Daniel
Additional Editing
Brittany Flynn

© WGBH Educational Foundation 2016



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