My BIL routinely treated his toilet for mineral stains with diluted CLR
(phosphoric and oxalic acid). Now it's pitted. A wet pumice stone has
long been recommended as a safe way to remove mineral stains from
porcelain, but I've read that it can ruin some toilets.
Are there different qualities of porcelain for toilets, sinks, and tubs?
Are there some that can't be cleaned safely? How can you tell if
you're buying a good one?
I've read that bathtubs can be restored. Are some methods better than
others? Do any work on toilets?