Enamel bathtubs are not impervious to rust stains. Rust, which exists in water with high iron content, forms rings around tub walls and drains, which are unsightly. To remove stains, use one of several techniques. The effectiveness might vary based on your type of tub and the condition of the stain. Oxalic acid, also known as wood bleach, comes in crystal form and removes rust stains. Pumice stones also remove the stains. Attempting one or the other will reduce or remove stains completely to return the clear shine and finish of your enamel tub.
Dip a pumice stone in water, or pour water from sink faucet onto the stone.
Apply the stone directly to the stain and scrub the stain lightly until the rust stain comes off. Work the stone back and forth over the stain as needed.
Wash away the residue from the stone with clean water from the tub or a bucket, or clean and rinse the tub with a tub cleaner and sponge to remove residue.
Fill a bucket with warm water from the tub. Pour oxalic acid crystals into the water adding them slowly until crystals appear in the bottom of the bucket. This means the water is completely saturated with the oxalic acid crystals.
Brush the solution onto the stain and scrub with the brush. Allow the solution to penetrate the stain for several minutes. Brush on more solution and scrub away the rust stain.
Apply a rust remover from a hardware store to the stain. Let the solution soak in as indicated on the label of the product. Scrub the stain with a sponge or a towel, as indicated on directions.