Use what the pros use to detail your car at home! Magic clay is the safest material to remove contaminants (removes overspray, rail dust, brake dust, pollution) from you car's paint.
1. do not wash your car in the direct sun light,
2. do not wash your car if you car has recently been run. Must be cool to the touch.
3. do not wash your car using the clay bar with other cleaner (if cleaner PH 7 is ok).