Techniques may also be employed to make the blade stronger or harder. Copper and bronze can be
"work-hardened" by simply hitting the blade with a hammer while it is cold. Blades made of steel
with a high enough carbon content (greater than 0.2%) can be heat-treated by heating the steel
up to a critical point (most simple carbon alloys become non-magnetic slightly below that
point), then quenching it with forced air, oil, or water depending on the steel. Quenching puts
an enormous amount of stress on the metal, and often a sword would break into pieces during that
step. If the sword survived heat-treating, it would be tempered by heating it to a relatively
low temperature for an extended period of time. The tempering process would make it slightly
softer, but also tougher and "springier", and thus less likely to break or chip during everyday
usage.
