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Griots Garage has a clay bar made for glass. I spray on some of their speed shine first, then use the clay and clean up with their glass cleaner. It won't eliminate scratches or pitting but it makes the glass smooth, removes any film and leaves a nice clean surface.
It quickly removes acid rain spots, hard water spots, road film, stubborn bird stains, and that annoying interior glass film. Z-12 Clear-View Glass Polish™ is so effective, it even removes fine to medium scratches.
I asked a glass shop about scratches on the windshield of another vehicle I have, and his response was that the fix is a ball peen hammer. Then you can let your insurance company buy you a new windshield.
You would be better off to just man up and buy the new windshield. Buffing something that deep usually just causes distortion or overheating the glass will crack it. The money not spent on buffing supplies can be put toward a new windshield.
If you have scratches that are bad enough to be a concern......and obviously they are, then I would just replace the windshield.
I have used jeweler's rouge to remove some deep scratches from old CRT TV screens It's not easy to find but it is more aggressive than any of the available glass polishes that I have seen. I have never had the need to try it on my windshield.
We used to use toothpaste to remove very fine scratches or impurities.
You would be better off to just man up and buy the new windshield. Buffing something that deep usually just causes distortion or overheating the glass will crack it. The money not spent on buffing supplies can be put toward a new windshield.
I have had 3 new windshields on my C5 and it seems like a new car (for about 3 months!).