We are working towards improving the storage conditions of our audiovisual materials and one strand of that is the cold storage of rapidly degrading cellulose acetate based moving image films and negatives. We are also prioritising colour film as this is also unstable.
We have just completed a pilot project to store the most vulnerable of this material in a laboratory freezer, which has been an interesting project for the conservators.
Placing a film into the first polythene bag.
It is safe for this material to go below freezing as long as the humidity levels of the stored material remains at a stable, safe level. This is achieved using something called the ‘Critical Moisture Indicator’ method, which involves double-bagging the material into sealed polythene bags with an interlayer of dry materials (either dried boards or silica gel). Should there be any problem with the bags and the dry layer starts to absorb water, there is a blue indicator paper clearly visible which turns pink at higher humidities. The packages can then be reconditioned as necessary.
Image of full freezer – note the blue patches which indicate a safe level of humidity.
— Sarah Lewery, Conservator
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