Paint spatters usually don't have time to harden on a sink surface -- you usually see them before they do and wash them off. In the rare instances when you do have to remove hardened paint, you can use the same procedure no matter whether the sink is made of stainless steel, granite, cultured marble, enameled cast iron, ceramic, plastic, glass or another material.
Tools to Loosen Paint Splatters
In many cases, all you have to do is scrape the paint with a plastic paint scraper. If you're trying to remove a large, dried deposit of oil- or water-based paint, setting the edge of the scraper on the deposit and tapping the scraper with a hammer usually dislodges it.
If you can't get under the edge of the splatter with the scraper, spray some metal thread lubricant on the paint, and allow it to loosen the bond between the paint and the sink. This may happen quickly or it may take several hours -- even overnight.
Finally, Scrub Off Splatters
Once the paint has softened after spraying, then scrape it off with the plastic scraper or use an old toothbrush to scrub it. If necessary, apply a few drops of dish detergent while scraping or scrubbing to help lubricate the paint and make it easier to remove. Wash the spot thoroughly with soap and water when the paint is gone.
In same cases, you may need a solvent to emulsify the paint. If the paint is oil-based -- which you can recognize by its extra-glossy sheen -- soften it with mineral spirits or turpentine. You may also be able to soften it with rubbing alcohol, which is a good all-purpose solvent for water-based paint and lacquer as well.
If the paint is left over from a lacquer or polyurethane spraying project, moisten a rag with acetone or lacquer thinner, and wipe vigorously. Both are strong solvents, but neither will damage most sink materials, although lacquer thinner may have a dulling effect on a plastic utility sink.