Medieval sword tempering practice

Meteoric iron as the first usable steel; the discovery that hammering, heating, quenching, and tempering produce hardness and ductility. The Crusades-era legend of quenching hot steel by running it through a living slave.

So there's quenching and tempering. In the old days, some of the first steel that people ever had was basically meteoric iron. They'd find a meteor somewhere, and someone found that if you hammered it, it was malleable. Then someone found if you heated it up in a fire and quenched it, it would become brittle, but it became extremely hard. And then they found if you tempered it, you could get some of the ductility back, and you might lose a little bit of the hardness. The best swords thousands of years ago might be made of meteoric iron. Well, there wasn't a lot of meteoric iron, so only the kings had the meteoric iron things. But they did have wrought iron, and they learned how to make swords. And of course, during the Crusades, the best quenching — they used to take a living slave, and they would quench the hot steel by running it through the slave. Gave it the quality to kill, I guess. A lot of little things that people did in the old days that they don't do anymore.