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The vice inherent in photographic film

February 25th, 2012 By Mark Strange

For the first time in New Zealand, we have treated a large number of badly deteriorating acetate photographic films.

Most photographic materials are complex, a combination of composite and laminate structures, and this complexity entails some inherent vice. In the case of this picture, the clear acetate film layer that supports a coating of gelatin, suspending tiny grains of silver in the shape of the image, deteriorated while being stored in a humid environment.

Whites Aviation collection image before treatment.
Pre-treatment version of De Havilland Vampire aircraft, photograph taken by Whites Aviation, Ref: WA-29339-F.

In the photographic industry acetate is known as one of the safety films because it is not as spectacularly flammable as its predecessor – cellulose nitrate. Though less flammable, acetate film still shrinks, and becomes blistered and brittle. The image becomes disfigured and cannot be digitised.

A very tightly controlled storage climate arrests this kind of decay, and the Library's controlled atmosphere room for film is very dry and cool (30% Relative Humidity and 2°C). If you have camera film (negatives or slides) at home, it will almost certainly include some acetate.

Treating film that has decayed over decades before being acquired takes several days, a laboratory with solvent extraction facilities, and conservation expertise that is only found in New Zealand in the Library.

Treating the images

The acetate films are immersed in a sequence of solvent baths that dissolve the adhesive between the gelatin layer and the acetate support, letting us strip away the shrunken plastic. Freed of its unstable inherent support layer, the gelatin can finally regain its original shape and flatness ready to be digitised for public access.

Whites Aviation collection image after treatment.
Post-treatment version

As a conservator, I encounter small national treasures almost every day in my work. It’s immensely satisfying to be able to deliver new images to the public where they were previously inaccessible, and to return the beauty and logic of an image that might have been considered unworthy of being acquired or kept.

Until now, the process has only been performed on individual negatives. Recently a batch of 25 films was successfully treated simultaneously. This test batch lets us plan the treatment of over 2,000 similar negatives from the Whites Aviation and Evening Post collections, getting them ready for digitisation by Pictures Online.

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