I read several years ago that Pilkingtons had developed
a new kind of glass, with some kind of activated surface
which kept the glass clean.
IIRC, the glass was intended for use in very tall buildings
where it is impractical to clean from the outside.

I wonder if anything came of this?

--
Timothy Murphy
e-mail (80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland