Just for your reference
Clay bar
Clay is a mixture of clay base and various mild abrasives. Clay along with a clay lubricant is used to remove paint contamination. Road grime, tar, bugs, rust, tree sap and
even paint overspray can be removed with a clay bar. Clay bars differ in color and density but what is most important is the type and amount of abrasive particles they contain.
All clay bars will be labeled from "mild" to "strong" abrasive quality. Claying does not remove the clear coat of the paint but can cause marring or dullness if used incorrectly. When using a clay bar sufficient lubrication must be present to avoid scratching the paint. It takes a few passes of clay to feel the difference on the surface of the paint.
To evaluate the effectiveness of claying dry the area and assess the paint and the bar. The paint should become slick to touch. The clay bar used should be turning gray. If the clay bar is dropped it must be discarded. The clay bar should be folded over frequently to expose clean surface.
Claying does not replace polishing. It is a process that should be used before polishing compound is used.
Now today theres a new generation of Bar, they are not clay bar but will work much better, here's an example of some test I have done
What you see in the roof is overspray, the entire roof is FULL of it, actually the entire car, or what’s left of it, I was able to remove 99% of it
