Natural cleaners for brass include ketchup, soap or detergent, water, lemon juice, and a combination of vinegar, salt and flour. If the brass is lacquered (coated with a protective glossy finish), it can be easily cleaned with a wet paper towel.
Using ketchup or lemon juice, simply squirt and rub the tarnished area. Clean with a wet towel and buff dry.
Use soap or detergent if the brass is particularly dusty or dirty. Submerge the brass in warm soapy water and rub with a cloth. Use a toothbrush for difficult stains.
Vinegar, salt and flour can be used to create a cleaning paste. Mix 1 teaspoon of salt, 1/2 cup of vinegar, and enough flour for the mixture to become pasty. Rub the mixture on the tarnished brass and let it sit for 10 minutes, then rinse with warm water and buff dry.