New York, June 30 (IANS): The Statue of Liberty is an iconic olive-green symbol of American freedom. But did you know she wasn't always that colour?

When France gifted 'Lady Liberty' to the US in 1885, it was a 305-feet statue with reddish-brown copper skin. 

The colour change to the present olive-green happened as a result of about 30 years' chemical reactions with the air in New York City harbour.

"In her first few decades in the 'Big Apple', the statue slowly turned from that shiny copper colour to a dull brown and then finally to the blue-green we see today," according to a video produced by the American Chemical Society and PBS Digital Studios.

The copper skin of the statue continuously reacted with the oxygen in the air to form black-coloured 'tenorite' that gave the statue a darker brown hue.

The sulphuric acid in the air and the salty sea-spray around the statue then reacted with the 'tenorite' and produced 'atacamite' giving the olive-green colour we all recognise today. 

Researchers say that the olive-green coating on the monument protects it from further reactions, and the Statue of Liberty has remained this colour for over a hundred years.