Good question Mike but there's no real definitive answer.
I have some great pictures from working on the original factory paint on Wayne Carini's 1953 Hudson Hornet. The scary part is the factory paint was thin to start with, by this I mean paint that had NEVER been touched by human hands.
In this picture, I'm measuring the paint that was behind a "Dealership Badge" and my assumption is that it was bolted onto the trunk lid when the car was brand new and freshly arrived to the Hudson dealership.
Assuming, and I know this is usually not a good idea, but assuming the paint behind the dealership badge had never been polished, or anything, check out how thin it is....
Wayne Carini 1954 Hudson Hornet Original Paint Restored by Mike Phillips
This measurement,
LESS than 3 mils, was taken on a section of paint that was covered with a dealership emblem. While I was there Wayne removed it and it looked like it had never been touched. The paint in this area was NOT faded like all the rest of the paint on the car because it has been covered for
61 years.
This measurement was taken on the hood where the paint WAS visibly thin....
And for the hood on this car I carefully hand polished the paint while Wayne nervously watched....
It's hard to see in this picture here but where the yellow outline box is there's a thin spot showing black primer.
Here's the same spot from a picture I took with my iphone...
Close up cropped out of the original...
And this shot cropped out of the above shows the oxidation and cloudiness over the entire Hudson before restoring the original paint.
Most of the rest of the car, (except the hood), was buffed out using a Porter Cable 7424XP and a Griot's Garage 3" Mini Polisher with both Pinnacle Advanced Swirl Remover and Advanced Finishing Polish. I only used the finishing polish on the hood.
In the end, the finish had a uniform appearance....
After
Here's what I do...
When in doubt, and I think the paint is what I call whisper thin, I tread lightly...
The last thing I want to do is leave my signature in the paint. Se this article...
Your Signature - Don't leave one...
Don't know if the above helps but for what it's worth...
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