Incidentally, the enamel is still quite thick, and all my rubbing is only having a very superficial effect. Most of the solid which is released is silicon carbide from the paper. I don't want to try to rub deep enough to remove the iron stain, because of the risk of exposing the iron of the bath. I think the worst stain was caused one summer holiday when my pot plants were living on a wet cloth, which had, unbeknownst to me, a pin or something similar in it.

I also think that the reason I have not come across the automotive bodywork method before is that those who put forward the worst case scenarios for bath enamel are in the business of a) providing new baths, or b) providing new coatings for baths. Restoring the polish by polishing removes the necessity for either of these solutions.

Penny