Ceramic Sink

How do you get the spots of a ceramic sink?
I just moved into a house with a white ceramic sink. There are several and brown spots on it. I tried Comet, Magic Eraser sponges and Lime-Away. These products have nothing to remove stains. Always look exactly the same. Please help! His advice is much appreciated! Incidentally, I also tried soaking my sink with bleach right. Besides, I think the sink is porcelain.
Find a use of calling the CLR cleaning products as directed. It worked for me.