Glass coated with a very thin layer of titanium dioxide never needs cleaning. This is done through a special nano-scale coating of microcrystalline titanium oxide, which reacts to daylight. This reaction breaks down filth on the glass, with no need for detergent. When water hits it, a hydrophilic effect is created, so water and dirt slide off. Although it is slightly more expensive than conventional glass, adding about 15 percent to 20 percent to the cost of installation, the technology is already being used in sheltered housing windows where easy cleaning is important.

Right illustration

• 1 - Dirt, glass, Nano-scale Activ coating containing microcrystalline titanium dioxide
• 2 - Sun shines on window. The UV rays trigger a chemical reaction in Activ coating, called a photocatalytic process, which breaks down dirt
• 3 - When water hits glass, a hydrophilic effect is created. Water spreads evenly over the surface, instead of droplets, so runs off and takes dirt with it

I can't wait to do up the whole house in this stuff for Mother's Day. Those clever Brits, what won't they think up next? And remember when it was Americans who were ingenious?

BBC News June 8, 2004