I went after my kitchen sink with a stiff brush, with Comet, with steel-wool… Little or no progress.
But then I started just rubbing away at the worst crud with my thumbs…and it worked! It’s sort of like working at the glue that holds price tags onto plastic. It sort of balled up under my skin. The crud came away from the porcelain!
What the heck is going on here? And…do they market artificial thumb skin products that work the same way?
(My guess is that dead skin cells are flaking off and getting mixed up with the sink-dirt, to form a goopy wad of crud that sticks to itself more than it sticks to the sink.)
Use the edge of an expired credit card. It takes tight crud off much better than any store-bought scrub pad. Even burned on food from the inside of a pan.
You could probably use cooking oil to “melt” the goo. Let it soak in, then wipe with a paper towel. Then use hot water and a degreaser (such as 409) to get rid of the oil.