I have a white porcelain kitchen sink. For years, I have had two potmarks that just would not come off. I tried everything!
I tried Bon-Ami, I tried Ajax, I tried Softscrub, I tried Comet, I tried Mr. Eraser, I tried lemon and salt - all to no avail.
Last night I cleaned my sink after doing the dishes, as it was kind of dingy and gross. I reached for the cleanser, sprinkled it in, started scrubbing, and lo and behold! The pot marks were erasing! What the hell?
I looked down at the cleanser I was using. Bar Keeper's Friend! I forgot I had bought it, after reading about it somewhere.
It worked a miracle! I am happy.