Bob Vila's Tip of the Day: The first thing you need to know before polishing any brass object is whether the item is solid brass, or brass-plated steel, zinc, or cast iron. The easiest way to check is by placing a small magnet on the piece you’re not sure about. Magnets will not stick to solid brass, so if the magnet sticks, the piece is brass-plated. Plated items can be cleaned with hot soapy water, but rubbing or polishing them too aggressively can remove the brass plating.
HOW TO CLEAN TARNISHED BRASS...Add 1/2 c white vinegar & 1 T salt to a sink or basin (deep enough to cover the item). Fill with hot water & soak 15 - 20 min. Add some dishwashing detergent to a sponge and gently scrub with a circular motion. Use a toothbrush to get into the small cracks.