[ian@huth]

I have seen sprays advertised that give the window a coating which is supposed to make dirt less likely to stick to the window. Try googling for them. I think that these staqrted life as car windscreen coatings.

Pilkingtons now produce a glass which is specially coated called activ glass, I think. This coating reacts with sunlight tobreak down any dirt deposits on it and rainwater washes them from the glass.