Most stained glass projects end with an application of some sort of patina to change the color of the metal to some other color. Oddly enough, copper foil starts out copper colored (naturally), becomes silver colored with the application of solder, then returns to a copper color with the application of Copper Patina.
The black patinas simply turn your gray metals (solder, lead and zinc) to dark gray or black, depending on how long you leave the patina on before wiping it off.
All of these patinas are composed of nasty chemicals like sulphuric acid, copper sulphate, nitric acid, and selenium dioxide, so put on those protective gloves and get the kids out of the room.