Hi, there!
In my collection of badges and medals of russian submarines "Typhoon", more than 90% of the badges are made of brass (and hot enamel). You know the disadvantage of brass: it tarnishes quickly.
Each time I get a new badge, I wash it. I most oftenly use dishwashing liquid because it's very efficient to remove old dirtiness.
One day, I used this one:
On the following pictures, you'll see (in three steps) how this liquid cleaned and made the brass shine:
It's a matter of 1 or 2 minutes, simply using your fingers, then you just have to rince with warm water and to dry thoroughly . That's all!..