From: Bristol. United Kingdom
Registered: Oct 2007
posted December 26, 2016 04:48 AM
In my recent "Reminiscing" topic I mentioned about the introduction of red exciter lamps in cinema projection equipment. Perhaps members would like to learn more about this as I assume that few are, or were, employed in cinema projection.
Towards the end of the last century environmental concern banned the use of a lot of chemicals that were deemed toxic. In cinema projection rooms this meant the demise of the fabulous cleaner, carbon tetrachloride (CTC). Soon, black and white soundtracks disappeared from 35mm colour films to replaced by cyan tracks.
For a great many years the production of black and white tracks on colour films involved a lot of extra working processes produced by highly experienced staff. Some materials used in this process were toxic, the sound track received its own processing which was applied by a small wheel. The main ingredient was silver, but bleach and hydroquinone were also used. Copious amounts of water were used to thoroughly wash the film.
So, in the early years of the 21st century the soundtrack was changed to cyan dye optical tracks. The original exciter lamps produced large amounts of infra-red light, but cyan sound tracks do not absorb such light.
Cinemas had to change to red LED or laser exciter lamps, these would also be able to read the old black and white sound tracks with no trouble.
It is alleged that the change has saved 2,000 kilograms of silver and 150 million litres of water each year!
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