Water etching
 

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Not on a Vette but GM truck. My son parked his truck by a industrial Cooling Tower. This is what his paint looks like now. I tried clay bar, swirl remover and a light polishing compound with no luck. Any ideas without going to a professional. 2017 Chevy Silverado.
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At the end of 1994 I purchased a new Black 94 Corvette Coupe that sat in the dirt lot for months at a dealership, in Mesa Az. The car was a filthy mess and they spent 4 hours detailing it. The water spots were still visible when looking at the surface from a flat on angle. I tried clay bars, vinegar and over 10 other non abrasive products trying to remove these baked on water spots. I finally found something that would remove the water spots that I and the detail crew at the dealership could not remove. The product's name was The Wax Shops Safe Cut. Years later I couldn't find this anywhere and searched high and low. Then I found out that Turtle wax bought them out and the products formula. It was then incorporated in Turtle Wax's Polish and Rubbing Compound in the Black and Green bottles. When it was first introduced their advertising cracked me up, "Nano Technology" was the game. lol I'd try the Rubbing Compound in the green bottle. I also use it on clear polycarbonate, it's not abrasive.

I see a ton of swirls, so I am assuming you tried the "light polishing compound" by hand. I wouldn't use anything less than a heavy compound and microfiber cutting pads with a machine.

cutting compound with a DA polisher and cutting pad. That should get it plus clean up your paint nicely.

The Turtle wax brand is what I used compound and the swirl scratch remover. No luck. I have a machine just scared to use on a dark color like that.

Stuff like that, likely Megs D300 w/ Megs microfiber cutting disc will clean up nicely. If using a DA like a Porter Cable, Harbor Freight or Griots, low (speed 4) and slow (hand movement) is the way to go with that combo. 6 passes, 3 up 3, down alternating cross hatch. Start with 4, see what that gets ya adjust from there. Clean/fluff microfiber pad (compressed air or brush) after finishing each 18" x 18" section.

Yea, the polish obviously didn't make a dent since there are still swirls. Need to bring out the big guns to fix that...if its fixable.