Your car can look spotless yet still feel rough. Slip your hand into a thin plastic bag and glide it over the paint, and you'll feel the grit: rail dust, road fallout, tar spots. Washing doesn't remove it, it's embedded in the paint.

An iron remover dissolves this by chemically converting metal particles. The product turns purple where it reacts: that purple colour change is proof that the particles are releasing. You then rinse the liquefied residue away and your paint is free of embedded metal particles.