Green compound

Here's a picture of a bronze statue I saw yesterday in Budapest. 

Bronze is an alloy of tin and copper. This statue was a nice shiny when it was made but now over a hundred years later it's all green. 

This is the question; what is the green compound? Bonus points if you can explain what an alloy is and name the alloy that is made of copper and zinc. 

Answers to my school email address and prize for the best answer. (CE candidates - this is a compound you should know all about)