Paint scratches
Assess a scratch before polishing: appearance and simple tests cannot measure its depth or the remaining clearcoat.
The depth and the paint system change the decision
A scratch is physical damage to a surface. A fine mark in the top paint layer and a gouge exposing the substrate are different repair problems even if both are described as a scratched car.
On a basecoat–clearcoat finish, abrasive correction normally works in the clearcoat. It cannot replace missing colour, primer or metal protection. A defect can also be too deep to remove safely even if it has not completely penetrated the clearcoat.
A visible line is a clue, not a layer measurement
A groove can scatter light and appear pale, but a pale mark may also involve transferred material or exposed lower layers. Colour alone cannot identify the damaged layer. Clean appropriately before assessing the mark, without grinding contamination into the surface.
A scratch becoming less visible when wet does not mean it has healed, and it does not prove a safe polishing depth. The optical change is temporary. Do not scrape at the mark or lift a paint edge to investigate it.
Use several observations together
Inspect clean, dry paint under suitable lighting from several positions. Check whether coating is cracked, lifting or missing, and consider previous refinishing. A fingernail-catching description is only a rough screening clue, not a reliable clearcoat-depth test.
A common paint-thickness gauge reports total coating, not scratch depth or remaining clearcoat. Measurements can inform the decision but do not turn a photograph or simple test into a guaranteed diagnosis.
Improve, leave or refinish
For a suitable sound gloss finish, a small controlled polishing test may establish whether an acceptable improvement is possible. Stop at the required result rather than pursuing complete removal at any cost. Hand polishing is still abrasive.
A deep isolated mark may be left partly visible to preserve paint. Missing colour or exposed substrate can need an appropriate touch-up or refinish repair. Promptly assess exposed metal because protection is compromised, without assuming the same corrosion mechanism or timetable for steel, aluminium and plastic.
Do not confuse every defect with a scratch
Swirl patterns and polishing trails involve fine surface marks, while water deposits, chemical etching, chips and bonded contaminants have different mechanisms. A chemical cleaner cannot put back paint lost to etching, and abrasive compound is not the first response to every stain.
Reduce new damage by removing loose dirt before contact, keeping wash media clean and avoiding repeated dry rubbing. After correction, choose care appropriate to the finish. A wax or glaze changing visibility is not proof that a scratch was removed.