The ascetic acid in white vinegar can remove rust from porcelain. Apply white vinegar to the object using a paper towel or sponge. Completely saturate the rusty areas. After waiting 30 minutes, scrub off the rust with a scrubbing pad. Use a damp paper towel to wipe away the rust and vinegar. Dry the porcelain completely.
Lemon and Borax
Mix 2 parts borax with 1 part lemon juice to create a thick paste. Apply the paste to the porcelain with a paper towel. After completely covering all the rust with the paste, wait 20 to 30 minutes for the paste to work on the rust. The citric acid in the lemon juice and the tiny particles of the borax both break down the rust. Use a steel wool pad to scrub the rust and the paste. Wipe away the rust using a paper towel or sponge. Rinse off the porcelain and dry completely.
Salt and Lime Juice
Combine 2 parts table salt with 1 part lime juice. Lime juice has ascetic acid and the salt has tiny abrasive particles. Both work to remove rust. After applying the paste to the porcelain, wait for two to three hours. Use fine steel wool to scrub off the rust and then wipe the porcelain clean. Rinse off the paste with warm water and dry