In my bathroom sink there is black stain. It is a porcelain sink and I don't know if the porcelain has come off or something has gotten on to the surface. it is rough to the touch unlike the rest of the surface. What is it and how do I fix it?
Not being a plumber, but an owner of an older house, it sounds to me like the glazed surface of the porcelain has just worn away down to the cast iron in this particular area. It this "stain" located under an old drip? Is it located on an area of the sink that is constantly touched or rubbed? There are epoxy-type products on the market used to repair problems like this. You might want to give one of them a try
It is reight near the drain so yes, looks like what you said might be true that the porcelain has worn away. SO hwat are these epoxys that you talk about and how will that fix it?
After thinking about this, the products that I mentioned to you are probably not appropriate. These DIY kits are typically for small chips and cracks. Depending on the value of the sink (antique/character or just old) there are porcelain refinishing services that you can hire. My best advice: put "porcelain repair" into A yAHOO search. This might give you some ideas.