First remove the buckle & breastplate from the leather.
Next, do no harm.
You are not going for a mirror finish on a glassy smooth surface. The accumulated wear & dinks are a valid part of the surface of the brass.
Any attempt to use a wire brush or a wheel will potentially do serious harm to the objects.
Third, they must be cleaned. That makes sense ¿no?
The recommendation by my good friend who works on museum pieces is a little surprising, but it really works.
Just use toothpaste & an old toothbrush to scrub down the surface. Rinse & you are likely to be surprised at how it looks. Repeat using more toothpaste & a brush or rag until you get the luster you are looking for.
Note: A word of caution about using Brasso on your buckle & breastplate. As any of us who have used Brasso over the years can testify, it works great but it leaves a white deposit in nooks & crannies. It is maddening to clean those white deposits. Never, ever under any circumstances use Brasso on sculpture or historic objects.
The advantage of the toothpaste is that it is designed to rinse clean with running water.
Fourth dry your brass with a dry towel. Rub it clean with a cloth after you remount your brass.
Note: Don't use anything that will scratch the surface. A wire brush will clean, but it leaves a pattern of scratches behind.
A lady friend who restores antiques recommended this website:
Learn how to clean brass effectively with our tested methods using simple household ingredients like lemon, baking soda, and vinegar...
www.insideast.com
Any leftovers you can make soup with…