Here is a simple copper-brass cleaner . Make a concentrated solution
of vinegar and salt. You may then dip or brush the solution on to
the item. It is not super fast, but it works.
Dark Soy Sauce… yup, just soak your tarnished copper for a
while, then I use a toothbrush and good old Dawn liquid… Linda
It’s the salt and vinegar in soy sauce that cleans copper. I use
lemon juice, vinegar or hydrochloric acid and salt. It’s especially
good for cleaning my copper kitchen scales and pots.
Gold and Stone