Self-cleaning windows give pane relief

Rain plays an integral part in the performance of the new glass, as the product is activated by both sunlight and rainfall.Pilkington, which will launch its Activ self-cleaning glass this month, claims the revolutionary coated glass will 'virtually eliminate' the chore of window-cleaning.With impressive sales in test markets where a similar product is already on sale, the company also hopes it will boost sales of replacement windows and be adopted by architects for corporate clients.However, representatives of the nation's window cleaners reacted less favourably to the news.

The glass works using a microscopically thin layer of titanium oxide, a compound which is already commonly used as a white pigment in some paints, toothpaste, make-up and foods -- including the letters stamped on M&Ms.

However it is also known to have useful properties when applied to glass. In the 1970s, Japanese researchers discovered that titanium oxide could be activated by ultraviolet light, causing it to react chemically with dirt, breaking down organic molecules. This means that windows coated with titanium oxide will be activated by sunlight, and will then oxidise dirt particles, helping loosen their grip on glass.

A second intrinsic property of the compound helps to make the glass truly self-cleaning, Pilkington claims. Titanium oxide is also hydrophilic -- attracting water and causing it to form sheets on the surface of the glass rather than forming separate droplets and rivulets. This effect causes loosened particles of dirt to be washed naturally from the surface of a window during rainy weather.

In normal windows, glass repels water and creates beads and trickles which attract dirt and contributes to the familiar grimy windows as the water dries leaving behind marks and stains.

It may be wishful thinking in Scotland, but extended dry spells don't entirely eliminate the unique properties of the glass. The same cleaning effect can be achieved with a simple spray of a garden hose, according to the manufacturers. The windows then dry naturally -- and more quickly than ordinary glass -- without spots or smears.

While the technology behind the product has been known about for nearly 20 years, glass manufacturers have been working to find a way of effectively applying it to window glass.

Pilkington, and a rival company, PPG Industries of Pittsburgh, which has brought a similar product to market, apply it during the liquid stage of the manufacture of the glass itself. The resulting coating is so thin -- just 50 millionths of a millimetre -- that it is invisible to the naked eye and makes no significant difference to the opacity of a window.

Pilkington's Activ glass has already been successfully launched in US and European markets, and the company now hopes to see it adopted for both domestic and business use in the UK. Suppliers are expected to charge 15% more for the product than ordinary glass.

Rick Karcher, president of Pilkington Building Products said: 'It's not that you'll never have to clean your windows again, but the frequency and amount of time needed for cleaning windows will decrease significantly.'

A spokeswoman for Pilkington in the UK said the product was not available here yet because other countries had been used as guinea pigs: 'Because we are a UK company we were keen to test it elsewhere so that we know it is working really well before launching it at home.'

However, there are limitations. Rain or the garden hose won't help keep windows clean indoors, and the glass is only coated on the exterior side. Some critics have also queried what will happen to panes which are under the eaves of a house or otherwise sheltered from the rain and sun.

Meanwhile, the window cleaning industry is less than impressed with a development which threatens to leave them all washed up.

Andrew Lee, vice-chairman of the National Federation of Master Window Cleaners -- which has more than 2500 members across the UK -- said that he was 'sceptical' about the claims being made for the new glass.

He added that the consensus in the window cleaning industry was that the product would be unlikely to stand the test of time.

'Window cleaners certainly aren't quaking in their shoes,' he said. 'Like all new inventions we will be interested to see whether the claims made of this product will satisfy the commercial and domestic marketplaces.'

Lee said customers would demand high performance, as the glass is more expensive than conventional windows.

'Will it stop something like bird muck being baked onto windows by the sun, resist graffiti or kids throwing mud bombs? I suspect not,' he said. 'This is not going to wipe us out.'