Vinegar and magic eraser (melamine foam) will get pretty much anything off!
Not here with hard well water unfortunately… Hardened scale is quite robust against vinegar unless soaked. But either muriatic or phosphoric acid will do it, or hot citric acid. In descending order of effectiveness, as well as risk of giving yourself severe acid burns.
Sinks almost always look like this here as a thin layer of iron scale forms very fast.
citric acid
Everyone should have that stuff in the kitchen, honestly it’s generally more useful than vinegar, short of sweeping floors (vinegar evaporates, citric acid doesn’t). Get it in food-grade, still dirt cheap and you can use it in recipes for acid balance.
The second one is sodium percarbonate, which is essentially hydrogen peroxide stabilised with washing soda. It will de-grease just as well as washing soda with an extra kick, ideal to rinse preserving jars or get tea stains off metal tea sieves – also use that citric acid once in a while to get rid of mineral buildup. Generally speaking if soaking something in one after the other doesn’t clean it then it’s not dirty. You’re a home kitchen, not a chip factory.
Oh and do I need to mention that you shouldn’t combine those. Not that the reaction would create mustard gas or something, it’s merely useless (acid and base neutralise each other), quite exothermic, and a splash risk.
