What kind of sink is this? I’ve tried everything to get these marks out. Bar keepers friend, soft scrub, baking soda...the scratches are not coming out. Is this enamel or porcelain? Can it be restored and what kind of pro do I call for that? So frustrating we bought our house 6 years ago and it was renovated a few years prior and the sink has always looked like this. I don’t think these are deposits from pots and pans.