This only applies to impurities that don't dissolve in, or alloy with gold. For example, silver and copper cannot be removed from gold simply by melting because

This only applies to impurities that don't dissolve in, or alloy with gold. For example, silver and copper cannot be removed from gold simply by melting because they form solution alloys that don't segregate in the molten state. Some solution alloys of gold include crown gold (silver, copper, gold) and white gold (palladium, nickel, gold).