The difference between hard-rolled and special soft copper is caused by the methods of annealing. Hard-rolled copper can be rendered soft and ductile simply by placing it over a fire or stove until well heated, and then gradually allowing it to cool. Copper may be hardened by well heating and then plunging it for a moment in cold water, afterwards allowing it to steam dry. If kept submerged until cold the metal will prove exceedingly brittle. In repousse work soft copper will crack whenever the tool is applied too forcibly; these cracks may be repaired by soldering from the back.