Your car can look spotless and still feel rough. Slide your hand into a thin plastic bag and glide it over the paint, and you feel the grit: iron fallout, bonded road grime, tar spots and dust from brakes and railway lines. Washing won't lift that, it's stuck in the paint.

Decontamination is the step that frees it. A clay bar or clay mitt pulls the particles out mechanically, an iron remover dissolves the metal particles chemically, and a tar remover lifts the sticky black spots. What's left is paint that feels glass-smooth and that wax or coating finally bonds to properly.