Well, I did my "Glass Cleaner Abrasion" test this weekend.

I'll explain why I did it first. My car was sold at auction and then I bought it. After several months writing appeared on the windshield that you could only see in the morning dew. Stuff like "97 A6 Quattro" "VIN 40545..." etc. I tried Windex, alcohol, acetone and Goof Off to remove the left over crayon or whatever the substance was to no avail. I need to replace the windshield on my 85 pickup truck so I have a place to test and play. So I decided to do this experiment.

I applied each substance with a wet paper towel and rubbed the glass (the windshield on my pickup truck) in one orientation, back and forth 200 times. To determine if the glass was scratched I looked from inside and out at different angles. The experiment was pretty boring. I tried the following things :

Bon Ami
Comet
Soft Scrub
Glass Polish (comes in a hot pink can, bought at Ace hardware)
Copper pot scrubber
Steel pot scrubber
SOS pad
00 Steel Wool
GOJO Orange hand cleaner (Pumice)
Lan Lin hand cleaner
Toothpaste
Course (NAPA heavy duty) and Fine (Turtle Wax heavy duty) rubbing compound
(Course and fine determined on chrome truck wheels)

Turtle Wax One Step Car Wax
400 grit sandpaper
150 grit sandpaper

The only thing that visibly scratched the glass were both grits of sandpaper.

I may re-run the experiment with some "soft glass" or plexiglass to get a better feel for how abrasive these things are. A person on the forum mentioned some windshields will haze or get scratched with Comet. A local glass shop recommended 000 steel wool, dishwashing soap and great care. All I know is my truck must have a hard windshield. I though a steel pot scrubber or rubbing compound would leave a mark. Perhaps if I used a microscope. Humm, glass sample slides are usally pretty cheap glass too.

I used the glass polish on my 97 Audi windshield to remove the writing on the windshield. I tried the Bon Ami too but the glass polish seemed to "cut" better and faster. I also felt more comfortable using it. If I really believed my test results I would have gone after the windshield with a pot scrubber. ;-) I polished the entire windshield and it looks nice and smooth and beautiful. Also found some little tiny tiny rock hits maybe Novus can take out.