Messy Science

I knew that a combination of white vinegar and bicarbonate of soda could be used to clean tarnished metals.
The same can be said of tomato ketchup (or any sauces for that matter) as indicated in this picture.
Only 25 years worth of oxidation to remove from this copper planter which has been languishing in the greenhouse.

EDIT: 4 days later and a gooey mess, not sure this is the way forward. Might dunk the whole thing in a bucket of vinegar and bicarbonate.