Rapid Formation of Copper Patinas: A Simple Chemical Demonstration of Why the Statue of Liberty Is Green

Abstract

Copper metal is slowly oxidized when it is exposed to the atmosphere for long periods of time, forming a blue-green coating called a patina. For example, the green color of the Statue of Liberty is a result of patina formation. A wide variety of Cu 2+ compounds are found in patinas, and they generally take long periods of time to develop. Here, an activity is presented in which patinas are rapidly generated on the surface of copper-containing coins. The process can be carried out using very simple materials, making this activity suitable for a wide range of audiences, and also for courses offered in an online format. Because the development of the patina occurs within tens of seconds, the experiment can be presented as an in-class demonstration. Given the vast number of conditions that can be varied in this activity, it is highly amenable to exploratory learning exercises.

Overview of the challenges and current solutions in organic and hybrid coatings for historical monuments and architecture

“…Degradation of steel and other metals occurs by oxidation of the exposed surface, where metal oxides are formed on the exterior surface causing changes in color and structural integrity. 14 The final natural form of chemical weathering is efflorescence, where absorbed, trapped, or covered moisture transports soluble salts such as calcite or other alkalis within the material to the material's surface as it evaporates, forming crystalline salt deposits leading to structural strain or surface disfiguring. 15,16 This process occurs more readily in porous substrates and the manner of salt formation determines the influence on the overall structure.…”

“…These organisms secrete acidic solutions/plant roots, which cause a localized dissolution of the underlying porous materials. Degradation of steel and other metals occurs by oxidation of the exposed surface, where metal oxides are formed on the exterior surface causing changes in color and structural integrity 14 …”