Air molecules are charged with antistatic bars: high voltage is applied to sharp tips, which ionises the air, i.e. the air picks up the charge.
The ions are attracted by the opposite charge on the material surface and migrate there (up to 1500mm without additional air support).
The air exchanges the charge on the surface and neutralises the surface almost completely.
The ionization takes place in a pulsed manner – plus and minus are never generated simultaneously, but are clocked.
No surface is really smooth, but the air molecules reach “mountain and valley”.