Certain impurities can have disastrous effects on the cast quality and workability of precious metal alloys. One of the worst and most common of these is lead, which present even in minute quantities can wreak havoc in a goldsmith's shop by rendering the components brittle and unworkable. In some cases, cracking will appear during annealing or welding operations following working.

This is due to the fact that lead will no actually alloy with gold but forms a distinct intermetallic gold/lead phase having a melting point of 418'C. As soon as the grains are completely surrounded by this phase, the grain structure effectively ceases to be bonded together and attempts to work, bend or even subsequently heat the metal will literally cause it to fissure apart. Lead contamination may occasionally be traced back to certain fluxes or deoxidants which can be minutely lead-bearing. Some zinc-bearing gold alloys utilise brass as a "master" alloy in their preparation. Since many "free cutting" industrial brasses contain lead, this is also a possible source. Once lead contamination has occurred in a workshop it is difficult to purge. Strict precautions should be taken, thus, to avoid this.