Why do statues go green?

The green coloration of statues, also known as patination or verdigris, is primarily due to the chemical reaction of copper with oxygen and water. Copper is a common material used in creating sculptures and architectural elements due to its durability and resistance to corrosion. However, when exposed to the elements, copper undergoes a process called oxidation, where it reacts with oxygen to form copper oxides.

The reaction of copper with oxygen and water leads to the formation of various copper compounds, including copper carbonate, copper sulfate, and copper chloride. These compounds create a green-colored layer on the surface of the copper, giving statues and other copper objects their characteristic green hue.

The specific shade of green can vary depending on the environment and the composition of the copper alloy used. Factors such as humidity, acidity levels, and the presence of pollutants can influence the rate and extent of patination, leading to different shades of green or even other colors, such as brown or black.

It's worth noting that not all statues turn green. Materials like bronze, which is an alloy of copper and tin, can also develop a patina, but it may appear brown or black rather than green. Additionally, some statues are treated with coatings or preservatives to prevent or slow down the process of patination, maintaining their original appearance.