Patina
A patina is a chemical finish applied to the solder lines of a leaded or foiled panel to change their colour. The most common patinas turn the silvery solder black or a copper colour, which gives the lines a finished, traditional appearance and hides the contrast between the lead and the solder.
The patina reacts with the surface of the metal, so the panel must be clean, and it is washed and then waxed afterwards to stop the colour from rubbing off. The term is also used, in a general sense, for the natural dark film that forms on old lead came over many decades.
Patinas are usually strong chemicals and should be handled with gloves, with good ventilation.