How do I remove this embedded stain from bathroom sink?

It appears cracked somthe stains have set in.

I would fill the sink with water and add some bleach. Let it set and the stains may disappear before your eyes

Vinegar also works with baking soda as a paste.

Put gloves on and get a toothbrush and pour this on the tooth brush and scrub it on, watch your eyes!!! Let it sit for a couple minutes , scrub, and rinse. Repeat if necessary. It is very powerful stuff! https://www.target.com/p/lysol-toilet-bowl-cleaner-with-lime-and-rust-remover-2-ct/-/A-14897134?ref=tgt_adv_XS000000&AFID=google_pla_df&fndsrc=tgtao&CPNG=PLA_Grocery%2BEssentials%2BShopping_Local&adgroup=SC_Grocery&LID=700000001170770pgs&network=g&device=c&location=9005835&ds_rl=1246978&ds_rl=1247077&ds_rl=1246978&gclid=CjwKCAiAkrTjBRAoEiwAXpf9CQgAorJ3CpAYPZ53ysOZCMqJ-rd4DUZqLMIRqw6AbJxgdfp9bmvcYBoCTY8QAvD_BwE&gclsrc=aw.ds

I'd probably start by shutting the stopper and using bleach. If that doesn't work then I would try other things in the clean-up arsenal; MrClean, Barkeepers Friend/Comet, etc. Good luck.

Me again. From looking at it again, -maybe rust remover would clean it up including the stopper. I use 'Wink rust stain remover'. Pretty sure I get it at Walmart.

To me it looks like there was a large drain cover at one time. It's pretty evenly round like something sat in that spot and stained or discolored it. You will scratch the shine using a pumice stone on polished porcelain so I don't advise that. There is a product called ZUD that will take rust off of [orcelain tubs etc. Give that a try. It worked in my sons 150 year old house (of course the bathroom was not that old) so it's pretty good stuff.

It looks like the porcelain is worn off. I had an old kitchen sink with the same thing. I was told either paint it or get a new sink.

I think Beth is right. I had the same problem on the bottom of my 50 year old bathtub. The more I scrubbed, the worse it got! Turned out I had scrubbed the porcelain away.

It's hard to tell. Try closing the stopper and letting Lime-a-way or CLR soak over night. If that doesn't work, it must be no porcelain.

Beth is right. You'll also get the same kind of thing with fiberglass sinks, but the "stain" will look yellowish...its the fiberglass. Any bleach or peroxide products will dull and eventually remove the shiny finish from your fiberglass sinks or tubs, so they recommend using a cleaner approved for use on pvc. I've been so careful to not clean mine with bleach products, yet got the "stain" anyway...palm to forehead, toothpastes have peroxide in them! aarghghg!

IF ALL ELSE FAILS AND YOU DON'T WANT TO REPLACE IT - PAINT IT..