I try not to use a lot of harsh chemicals at home because me and the homefries are crazy enough as it is without adding something new to the mix. I have a couple of really nice vintage kitchen collectables that have gone dull over the years but with this concoction made from easy-to-have-on-hand ingredients, well now they are shiny and almost newish again.
Disclaimer: depending on the age and/or condition of your copper, you may not get an as-good-as-brand-new shine, and I found mine had a bit of streaking once done, but overall for a quick shine, it gets the gunge off pretty easily. Best bet is to test run on an inconspicuous section of your item and see if it suits your needs.
Dirty Copper Flour Polish
Mix together the following in equal parts:
Rub a thin layer of the mixture on the item you want to shine up.
You can adjust your mix to match the size of the object(s) you're trying to shine up. To do all three pieces shown in the photo, I mixed up five measured teaspoons of each ingredient.
I found many different combos of this formula online, some use water, some don't, so feel free to experiment and find what works best for you.
I ran each piece quickly under cool water and then toweled them dry to remove any residual polish. I am pretty happy with the end result.