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Active Ventilation
Active Ventilation
Because the efficacy of acid scavengers is limited by the
slow diffusion of acetic acid vapours, ScreenSound Australia has been
experimenting with methods of ventilating film cans. It was found that simply
punching some holes in the enclosure is ineffective in lowering acid
concentrations inside a film can. They have therefore been investigating more
active approaches to ventilation. They have determined that the best way of
ventilating a film can is to have the air flow in the vault pass through two
holes in the film can which are directly opposite each other. The positive air
pressure from one side to the other helps ventilate the film can. Further
experiments varying the design of the film can and shape of ventilation holes
are under way10.
Dr Ngo Hieu Chi of the Vietnam Film Institute has developed
a treatment method whereby films affected by Vinegar Syndrome are unrolled and
exposed to a ventilator for 36 hours. The amount of acetic acid in the film is
reduced by 90-95%, and the life expectancy of the film is increased by about 3
years (with subsequent storage at 14ºC and 40%RH). This allows more time
for duplication before the film becomes unuseable (Ngo Hieu Chi, 1998, Annex
Q).
Evaporation of the acetic acid reduces the rate of
deterioration of the film, however, it also leads to accelerated shrinkage.
According to Dr Ngo, this method is most effective if the acid content of the
film is still relatively low between 0.7% - 6% of the total film weight,
or 50-400 mg per meter of film for 35mm film. In this case, shrinkage is
restricted to about 1.5% 2.5%, and the film remains useable (Ngo, 1998).
If the film is severely deteriorated, evaporation of the acetic acid results in
shrinkage of over 3%, and the film becomes unusable.
(10) For further details, contact Mick
Newnham at ScreenSound Australia
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