Extensive manual work, such as hand-raising a sheet, will often involve working on a soft former to prevent surface damage. Such soft formers are often made from lead.
Lead forms brittle inter-metallic phases in gold and platinum alloys. Hence, if lead-based residues are left on the surface during annealing (to restore ductility during working), the lead can diffuse into the gold.
On further working, the lead impurities can lead to embrittlement and failure of the jewelry item.
The use of metallic lead in contact with gold and platinum metals is always risky. If considered essential, the piece must be separated from the lead by interleaving it with a tough grade of paper.