Brass, an alloy of copper and zinc, has been used to make decorative objects for thousands of years. Brass is more tarnish-resistant than other metals, however, it will tarnish when it is exposed to moisture, oxygen and sulphur in the air. In most cases, the tarnish doesn't harm the brass, merely turning the surface of the metal dark and dull. While there are numerous products on the market that will remove tarnish, you can easily make tarnish-removers from household products you have in your pantry or cleaning closet.
Ketchup, which has a pH of approximately 3.0 to 4.0, is one of the most effective tarnish-cleaners around. Simply rub some ketchup into the tarnish with a soft cloth and allow it to sit on the surface for a minute or two--or longer, depending on how heavily the item is tarnished. Then rub the ketchup and tarnish off with another clean, soft cloth and buff the brass dry.
Acidic lemons clean tarnish in much the same way as ketchup; the acids in the lemons dissolve the tarnish from the surface of the brass. You can either squeeze some fresh lemon juice onto a rag and rub onto the brass, or cut a lemon in half and rub the lemon directly onto the surface. Wipe away the tarnish, then wipe with a clean rag and warm water. Dry the brass piece completely after cleaning.
Combine 1/2 cup of white vinegar with a teaspoon of salt, then mix with plain white, unsifted baking flour until you have a wet paste. Wet your tarnished brass piece with warm water, and then coat it with the paste. Allow the paste to sit for approximately 15 minutes, then rinse well with water and dry thoroughly.
Household ammonia works to loosen and remove tarnish through a mild chemical reaction. In a well-ventilated area, put on rubber work gloves and either dip or spray the tarnished brass with a solution of 1 part ammonia to 8 parts warm water. Wipe away the tarnish with a soft cloth, and then rinse the piece completely with clean water. Buff dry.