Why the Statue of Liberty is Colored Blue Green | Chemistry Articles

Why the statue of liberty is colored blue green?

Why the Statue of Liberty is Colored Blue Green

Most people are acquainted with the Statue of Liberty which really is a gift from the individuals of France to the individuals of the United States. The Statue of Liberty represents Libertas, the Roman goddess. She holds a torch above her head, and in her left arm possesses tablet inscribed "July 4, 1776", the date of the American Declaration of Independence. A damaged chain also lies at Statue’s feet.Then after the statue became an icon symbol for freedom of the United States and was a welcoming sight to immigrants arriving from abroad.

The Statue of Liberty is 305 feet and 1 inch from the bottom to the tip of the flame, which can be the exact same height as a 22-story building. When the statue was originally assembled, it was a dreary brown colour, reflecting the natural colour of its copper plates. Over the next 30 years, it slowly looked to the iconic blue-green colour.

But how did it happened?

The Statue of Liberty is coated with a slim layer of copper, which can be turned into a blue-green with age due to chemical reactions between metal and water. This process is known as patination.

Why architects use patina?

Architects sometimes request a specific patina colour at installation the projects. Factory-applied chemically induced pre-patination systems could make a wide range of coloured finishes much like natural patination. Pre-patinated copper is especially useful for repairs if you have a need to supply close colour matches to old copper roofs.

Patination process

Most people know copper reacts with air to create verdigris, nevertheless, the Statue of Liberty is its own special colour because of its unique environmental conditions. It's not a simple single reaction between copper and oxygen to generate a green oxide, like you may think. The copper oxide continues to react to make copper carbonates, copper sulphide, and copper sulphate.

There are three main compounds that are responsible for forming the blue-green patina: Brochantite [Cu4SO4(OH)6] will give green; Malachite mineral [Cu2CO3(OH)2] which also give green and Azurite mineral [Cu3(CO3)2(OH)2] gives blue.

Initially, copper metal reacts with oxygen from the air in a redox reaction. Copper donates electrons to oxygen, which oxidises the copper and reduces the oxygen:

2Cu + O2 → Cu2O (pink or red)

Then the copper(I) oxide continues to react with oxygen to form copper oxide (CuO):

2Cu2O + O2 → 4CuO (black)

At the time the Statue of Liberty was built, the air contained a lot of sulphur from air pollution produced by burning coal:

Cu + S → 4CuS (black)

The copper sulphide(CuS) reacts with carbon dioxide (CO2) from the air and hydroxide ions (OH-) from water vapour to form three compounds:

2CuO + CO2 + H2O → Cu2CO3(OH)2 (green)

3CuO + 2CO2 + H2O → Cu3(CO3)2(OH)2 (blue)

4CuO + SO3 +3H2O → Cu4SO4(OH)6 (green

The speed at which the patina develops and colour depends on the humidity and air pollution, not just the presence of oxygen and carbon dioxide. Patina develops and evolves over time.

© WOC Article

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