Brasses are an alloy of copper and zinc. There are a wide variety of mixtures, for example yellow brass contains roughly 65% copper and 35% zinc whilst copper alloyed with zinc and tin is called gunmetal. Brass could be gilded, or coated with a tinted varnish to imitate gold.
Copper pieces could be 'brassed' by exposure to zinc vapour at high temperatures, or by boiling in hydrochloric acid and zinc amalgam. Iron could be electroplated or molten dipped in molten brass.