Cleaning

This is a copper (or maybe brass?) tray from Saudi Arabia. My uncle worked there for many years and sent this tray to my parents back in the 60s. They had it hanging on the dining room wall for a long time, then had a coffee table made for the tray to sit atop. Now it's mine. I decided to clean it, since it's probably been years since it has been cleaned. I made a little progress, which hopefully you can see as you compare the before picture on the left to the after picture on the right. The tray is about a yard wide, and my arm got too tired after a while. I'll have to work on it again sometime.