verdigris • \VER-duh-greess\ • noun

a green or bluish deposit especially of copper carbonates formed on copper, brass, or bronze surfaces

• Example sentence: It seems like every building on campus features some combination of brick, ivy, and verdigris.

• What I was doing wrong? : Most probably i would have used 'copper rust' or simply 'rust'. Had No choices dude, can't help it :)