The following images are taken from an experiment by one of our suppliers, examining the effects of limescale, lipstick, excessive rinse aid, heat and dirty glass washers on the quality of beer in glasses. They all use lager poured into a 'head retainer' glass, which has nucleation points etched into the base of the glass to promote foam generation.
Good Clean Glass
With a clean glass, you can see a crisp, clean 1cm tall head at the top of the glass, which is retained for a decent time. The lager is fizzy to taste, and the gas release is controlled. 15 minutes later: