Visible scratches, etching from acid rain and bird droppings, oxidation, and rock chips. The only way to completely eliminate these imperfections is to remove micro layers of paint down to the base of the scratch. This is not the best method as you always want to keep as much paint on the car as possible. In some cases you don't need to get down to the base of the scratch. Simply rounding off the "V" of the scratch and filling the remaining crevice with wax will reduce the visibility of the imperfection substantially.