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Silver screen no more

February 23, 2007 By Emma Marris This article courtesy of Nature News.

Greener film soundtracks win Academy Award.

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As the film world awaits the tearing of envelopes at Sunday's Oscar ceremony, some are already clutching their Academy Awards. Among them are the 12 technicians who, in the name of reducing pollution, have de-silvered the silver screen for good.

The team worked to replace the silver used in soundtracks with cyan dye, reducing the need for harmful chemicals and saving 2,000 kilograms of silver and more than 150 million litres of water each year.

Black-and-white films were made with silver printed on celluloid. The soundtracks ran alongside the frames as a silvery strip of varying thickness. A tungsten filament light shone through the soundtrack, and a photocell on the other side captured the light, and converted it into sound.

Colour film, developed in the 1930s, uses cyan, magenta and yellow dyes. But the tungsten lamps produce infrared light, which passes through the colour dyes and hits the photocell. So silver was added to the colour film soundtracks to blot out unwanted noise. This involved many extra processing steps, and used toxic chemicals such as sodium hydroxide and hydroquinone. It also made it difficult to dispose of old film.

The solution, devised in the mid-1990s by engineers at Dolby Laboratories in San Francisco, was to change the tungsten light to a red LED. "Cyan is as solid to red light as silver is to infrared," says Ioan Allen, vice-president of Dolby Laboratories, and one of the team that received the Academy Scientific and Technical award on 10 February.

Once the technology was built, it was a matter of convincing theatre owners to switch from tungsten to red-light readers. The first major release with a cyan soundtrack, a teen comedy starring Kirsten Dunst called Get Over It, came out in 2001.

In many cases, cyan soundtracks are now backups to digital soundtracks, which work by a different method. Nevertheless, all films still have cyan dye soundtracks, and the red light also works on old silver soundtracks.

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