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.

1. Why The Statue of
Liberty is Colored
Blue Green?
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2. 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.
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3. • 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.
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4. 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.
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5. 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.
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6. • 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)
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7. • 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.
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8. Thank You
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