Ketchup does work (obviously), though when I used it for brass, the result was not as good as from a proper polish.
Wright's Copper Cream or just about any metal polish would work fine as well. Blue Magic Metal Polish Cream does wonders for brass with minimal effort, so I imagine it would do as well or even better with copper (in my experience, brass tarnish is more difficult to remove than copper tarnish).
Anyway, glad you got your copper cleaned
