To test if you have a genuine porcelain tub, place a magnet to the side of the tub. If it sticks to it, then you have a metal tub with a porcelain enamel finish. Genuine porcelain tubs are more resistant to chemicals than porcelain enamel tubs.
You can also do this on a normal basis to keep the inside of your tub looking clean.
Or, you can combine 1⁄4 cup (59 mL) of ammonia and ¼ cup (55 g) of baking soda and use the paste to scrub away the stains. [5] X Research source
You can use a rag as an alternative to a sponge. Porcelain enamel is sensitive to harsh chemicals like bleach and vinegar, which can lead to further degradation of the tub. [7] X Research source
You can use a grapefruit as an alternative. [9] X Research source
The lemon will also create a shine and add a protective coating over your tub. [12] X Research source
