Q. I was reading your Stain Management Application about cleaning vinegar stains, and in the types of stains on the left, vinegar is not listed. I was hoping you could clarify what poultice and method to use. Vinegar diluted with water was used in an attempt to clean new, unfinished natural stone mosaic floor tiles (like river rock). It's yellowed so I'm hoping to remove the stain. The texture (finish) of the stone was not affected at all, just the color. I don't think etched or anything. I think it's fairly porous. They appear to have been tumbled and ground at some point to flatten them and take the edges off. (I'm an architect and have worked a lot with tile and stone, though haven't come across this). I put the same vinegar mix that was used on some leftover samples and tested my sealer on it. It appears to mask the discoloration. I have 2 sealers on hand. one is enhanced providing a wet look which seems to do a pretty thorough job. ( I can't see the discoloration) The other is a penetrating sealer that leaves the natural finish appearance alone. Obviously the latter is out. I'm almost afraid to do anything more to the natural stone for fear of creating more problems. The only remaining question is if the dried vinegar would affect the sealer over time. After 36 hours, I can't see the discoloration at all.