Why is the Statue of Liberty Green?

One of the inherent properties of Copper is its vigorous reactive nature with other elements. When Copper reacts with oxygen present in the air, it forms oxides, the process being termed as “Oxidation”. It is because of this reason that the external layer all over the Statue of Liberty has turned to Green color.

The product formed as after the reaction of Copper with oxygen does not turn into green just in one step. It is rather a limited chain reaction in which first a somewhat pinkish oxide is formed which undergoes further oxidation and transforms into a black colored product termed as tenorite or a blackish compound called copper sulphide. The blackish compound in turn reacts with CO2 coupled with sulfur dioxide in a relatively damp environment and finally turns into the said green colored coating. The most intriguing feature in this regard is that this outer film of oxidized copper shields the underlying copper from further decaying into oxidation. The resultant glossy surface contains three pigments, viz. brochantite, malachite, and azurite. The formation of this glossy surface chemically termed as “patina” is proportional to the relative amounts of humidity and a certain range of air pollution.

Statue of Liberty Why is the Statue of Liberty Green?

Under a minute scan if the surface of statue is carefully examined, one will learn that only a fraction of .005” thick oxidized film of copper has been able to develop in a century after being regularly attended by a homogenized interaction of precipitation, air, sun light etc. It is because of this reason that copper does not need renovation for centuries. It was just the torch of statue that underwent an improvisation and thus it was patinated on purpose to match its texture and hue to that of the statue itself.

The pennies, sub-units of western currency are not pure copper, yet they amply exhibit the phenomenon of “Copper Oxidation”.

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