What is the best way to clean brass?

use ketchup

I use bar keepers friend: https://amzn.to/2I0dh9m

I've also heard ketchup works as well, but I've never used it.

citric acid powder is mixed 2 teaspoons to a quart of water. The exact concentration does not matter too much. A half-ounce in a gallon of water also works. High concentrations are not needed. Citric acid is the active ingredient in home-made brass cleaners that use lemon juice. Same stuff.

To use, pour enough boiling-hot water into a large glass (or non-metal) bowl to cover your dirty brass. Add the citric acid and give it a quick stir with a non-metal spoon. Then dump in your brass, and stir or swirl the container for a couple seconds. You will see the tarnish and dirt being removed almost instantly. Usually takes only a few seconds to a minute or so, and it's done-- there is no need to soak for a long time. The brass will look almost like-new, cleaned inside and out. Rinse the brass with clean hot water, and set aside to dry. You can polish after drying, and brass treated with this solution polishes quickly. To reuse the solution later, just reheat it.

The advantage of citric acid is that it will not penetrate or damage the brass like ammonia-based brass cleaners will, and it works even faster. Also, citric acid passivates the brass, which means that after washing in the hot solution, the brass is actually made more corrosion-resistant. If you store brass for long periods, that's great news.

Brasso

Ketchup

You can buy cleansing creams made specifically for brass. I used to use it to polish my antique brass bed. Check at home improvement stores or hardware stores. You rub it on and wipe it off. It is time consuming but not hard.

Mix equal parts, salt, vinegar and flour and rub on. Clean well after to remove any residue.