My very old apartment building built in 1925 has 24 cast iron bath tubs. Does anyone know of an effective cleaner to make the tub insides clean again without expensive resurfacing?

Painting the outsides with Rustoleum works great, it is the inside that needs help.

Thanks

A "cleaner" will not work, because after that period of time, the glaze has been "rubbed off".

The cast iron tubs are glazed with powdered glass melted at high temperature. It is extremely difficult to polish this to a luster again once scratched. In some areas the glass is almost 1/8 to 1/4 inch thick. Currently Kohler applies two coats of melted glass to their tubs it is amazing they can sell it for the price that they do.

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There are tub refinishers that have proprietary products that they use for refinishing porcelain tubs and sinks. They typically do not like doing toilets because they can't get down into the throat and they are labor intensive to finish and cheaper to replace unless there is an old color you are trying to match. Like all products some are better than others so do your research on the net and call your local plumbing wholesalers. The guy I used to know had contracts with hotels and motels as he could refinish for less than they could replace so he had regular business with them. Maybe that could be a lead for a recommendation to a vendor. Good Luck.