Use white vinegar to wet and saturate tub bottom and sponge. Next, take baking soda and sprinkle on wet surface as well as vinegar saturated sponge and scrub bottom of tub. Open a window or ventilate the room as the vinegar smell can be a little overwhelming. It takes a little elbow grease, but works well. It will foam also. This is the same ingredients used to make volcanoes for school projects !!! These ingredients will not harm the surface of the tub.

Have had several cast iron tubs. I would soak the areas in pure bleach. DEFINITELY vent the room and when you go back in after an hour or so of soaking - wash it out really quick! (holding your nose ;)

TNLady

I tried the vinegar and baking soda and it is taking some elbow grease, but what a difference! It really works.

I'm curious about the bleach option. I had thought of that, and it would be less labor intensive, but I thought I had read somewhere that the finish would be damaged by pure bleach. If TNLady has had success with it, I may use it later on to maintain the new white look. Thank you!

If it's really porcelain on cast iron, bleach won't hurt it.
Linda C

I have a suggestion for all bathroom and kitchen(VERY hi-concentrated, all purpose cleaner) cleanups. I couldn't believe how it worked but it did it before my eyes--a Conklin product called MOX. I happen to be a Conklin Distributor, so give me a call(402-617-5542) if you have cleaning problems that you cannot solve.

Magic Eraser got our scratched tub spotless. It took 2 erasers to do the job

Try soft scrub with bleach and a scrubbie pad, or comet cleanser with a scrubbie pad.