Care for a cast iron bathtub by rinsing the surfaces after each use and wiping them down with a soft cloth. Avoid use of abrasive or acidic cleaning materials, including white vinegar, whenever possible as they can etch the surface and dull the shine. If the tub has a nonslip surface on the bottom, clean it with a soft nylon brush.
Cast iron tubs have a porcelain finish that the factory bakes onto the metal. It is durable but subject to chips, cracks and wear over time. Choosing the wrong type of cleaning products accelerates the wear.
Clean the tub weekly with a solution of grease-cutting dishwashing liquid in hot water. Apply the solution with a soft rag or sponge, and scrub the surface, paying close attention to any bathtub ring. Rinse and dry the tub after cleaning.
If moving into a new home with a dirty cast iron tub requiring deep cleaning, mix 1/4 cup of baking soda and 1/4 cup of ammonia in a bucket of warm water to clean the porcelain. The ammonia is an effective grease cutter, and baking soda provides slight abrasive powers without scratching porcelain. After rinsing, wipe the tub dry with a soft towel to prevent the formation of a white film from the baking soda.