Cooper... that's why is green. Copper turns green because of chemical reactions with the elements. Just as iron that is left unprotected in open air will corrode and form a flaky orange-red outer layer, copper that is exposed to the elements undergoes a series of chemical reactions that give the shiny metal a pale green outer layer called a patina.
Copper got a protective rust film due to oxidation. Hence the color is now green. It took 30 years to change the color from copper to green.
Steel and copper
Really dude #google it
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