Okay, so you've heard about this nanotechnology thing, and you're willing to admit that it's going to mean smaller, faster computers, and the occasional odd chemical, and maybe a new and scary section for the science fiction wing of your local library.

But self-cleaning windows — that sounds like someone's trying to unload a shipment of weapons-grade balognium, right?

Not so fast — not only is this theoretically possible, such windows are actually being produced, by a British company called Pilkington Glass.

Pilkington makes specialty glass for auto windshields and buildings. Its nanotech variety is known as Pilkington Activ, and its invention was a finalist for Britain's MacRobert Engineering Award, a £50,000 prize.

Activ is glass that has been coated in titanium oxide, which is used in toothpaste and sun screen and typically occurs as a white powder. But scientists at Pilkington developed a titanium oxide film that is only 15 nanometers thick — so thin that it's transparent.

The titanium oxide does two things. When it reacts with ultraviolet light, it acts as a catalyst and causes organic dirt and grease to break down, without being altered itself. Second, the film causes the glass underneath to become hydrophilic — it causes water droplets to seek each other, forming sheets of water that drip off, rather than individual drops that would dry on the glass surface, creating spots and streaks.

The inventors of Activ liken the nano-scale film to an invisible squeegee. And so, although the technology may be so small as to be invisible, the effect is something we can all see