Some light surface scratches can be improved by controlled polishing, but deeper scratches that have removed paint cannot be polished back into existence.
The first step is to identify whether the visible mark is contamination, transferred material, a light defect within the upper finish or a scratch that has passed through the colour into primer, metal or plastic.
Polishing works by refining the surface. It does not replace missing colour or primer. Using an aggressive compound on a deep scratch can therefore remove healthy surrounding coating without solving the actual damage.
If colour has been removed, the area normally needs an appropriate paint-repair assessment. Where bare metal is exposed, restoring the protective coating also becomes important because corrosion can develop if the area remains unprotected.
A scratch combined with a dent or panel distortion requires body repair before final refinishing. Likewise, a deep gouge on a plastic bumper may require preparation of the plastic substrate rather than polishing alone.
A common fingernail test can provide a rough clue but is not a reliable professional diagnosis by itself.
For a complete explanation, read Types of Car Scratches and Repair Options or see our Scratch & Dent Removal service.