One of the first lessons in jewelry making involves the concept of work hardening. The most commonly used example to illustrate the concept is the familiar experience of bending a paperclip wire back and forth until the metal finally snaps. The wire starts out flexible so what makes it eventually break? The answer is work hardening.
Many beaders have experienced the effect of work hardening when making simple wire loops. Sometimes you can break a headpin or a wire when repeatedly trying to get a coil just right. The breakage is not due to bad metal it has just been work hardened by too much movement.
Bending, hammering and shaping metal wire or sheet put stress on the metal. Those metalsmithing tasks are actually moving molecules within the metal solid to a point where they are no longer able to absorb pressure. At some point they will literally crack or break the metal.
When you are working a piece of metal you will feel that it begins to resist alterations as it work hardens. The good news is that most jewelry metals are easily softened or “annealed” to make them workable again. In fact, you can go through many cycles of work hardening and annealing on a single piece of jewelry.
When you feel the metal start to harden, immediately anneal to avoid breakage. Annealing too soon will not be a big problem but waiting until it is too late may cause irreparable damage to your piece of jewelry.
To anneal a metal you must bring it up to a critical temperature with a torch and then quench the hot metal in water. Be careful not to heat metals beyond the annealing temperature to their melting point. A good guide is a sharpie marker mark on the metal surface. The mark will burn off near the annealing temperature of copper and silver, then you know to stop heating and quench.