I painted this oil study from observation to study how actual bronze surfaces weather. Note how the upfacing planes of the hat brim, the lapel, and the forehead are all oxidized to a light blue-green color.
The hollows and the downfacing planes weather in a different way as this photo shows. Instead of being entirely covered with a light blue-green oxidation, the downward planes tend to be darker and browner. This is because the downfacing planes are exposed to less rainwater. The top of the ball is also shielded from rain, and lacks oxidation. Wherever the planes face downward, the water is forced to flow in fixed rivulets. Each rivulet then becomes a line of oxidation.
You can play with this effect. This bronze head from the title page of Dinotopia: Journey to Chandara was entirely invented. Along the cheeks the rivulets almost look like the path of tears.
If the statue is in a public area, projecting forms are often buffed to a golden sheen from contact with the hands (or hides) of passersby.
As the rainwater drains off the statue, the dissolved oxides leave stains on the white marble below.
Tomorrow: Reply Card