Plain bronze colour is pale pink to yellow, depending on the type of bronze used. A patina is simply a dye or chemical reaction added, with heat, to the surface to change the colour. It is then sealed with a wax or varnish to preserve the colour. If left alone bronze gradually, and over many years, develops a dark green and/or red patina, as seen on this Early Iron Age bronze Horse Cheekpiece from the Lorestan Province of Iran.