Motion picture film preservation

Motion picture film being wound before packaging
Winding and examining film for preservation.

Film consists of a clear plastic base and a thin layer of gelatin emulsion containing an image made from colour dyes or very small particles of silver (in black and white film).

Historically, there are three common types of film base: cellulose nitrate, cellulose acetate and polyester. Film also comes in a range of widths or 'gauges'. The most common examples held at the Archives are 16mm and 35mm gauge cellulose acetate-based films. We also have some 8mm acetate films and a small number of 35mm cellulose nitrate films.

Motion picture film is at risk of three types of deterioration: chemical decomposition, mechanical damage and biological degradation. While these factors drive the Archives' approach to film preservation, they are not our only challenges. We must maintain the necessary equipment used to repair, clean or view films. This equipment is mostly obsolete in the wider film industry and consequently, harder to acquire or maintain. Another challenge we face is providing access and preserving our film holdings by ensuring the most effective use of changing digital technology.

Chemical decomposition

There are three main motion picture film bases that are each at risk from different types of chemical decomposition.

Cellulose nitrate

This film base is very unstable. It can react with humidity in the air to form nitric acid. As it deteriorates, nitrate film develops a sticky or greasy surface, a dark yellow or brown all-over staining, and a strong bitter or acrid smell. It is also highly flammable. Cellulose nitrate film was for all practical purposes only produced as 35mm film and used until the early 1950s. It is still found in collections, although there are only small quantities in the Archives' holdings.

Cellulose acetate

Cellulose acetate is known as safety film, and can be more stable than cellulose nitrate. Over an extended period, the film can shrink and become brittle as it reacts with humidity in the air to create acetic acid. This reaction is called 'vinegar syndrome' because the film develops a characteristic vinegar odour. Most of the Archives' holdings consist of cellulose acetate film.

Polyester

Polyester is the newest and most stable film base. It has been used since the 1960s for microfilm and is routinely used for picture theatre projection prints because of its physical toughness. It does decompose over time, but does so at such a slow rate that it does not pose a preservation risk.

Image loss

All motion picture film, regardless of the base, is susceptible to fading. Commonly, colour dye-fade results in an overall magenta appearance. However, different colour castes can occur according to the type of process and brand. Black and white film in general is a lot more stable. However, in adverse conditions the image can take on a silver mirror effect that can partially obscure the images. When cellulose nitrate-based film deteriorates, it can cause significant fading of the silver image.

Mechanical damage

Motion picture film can suffer perforation damage or breakage caused by incorrect threading of a projector or faulty equipment. Cement or tape splices are used to edit and repair films. Old tape splices can deteriorate and fail. Without careful handling, dirt or other contaminants can irreversibly damage the film image by scratching the delicate emulsion layer.

Biological decay

Mould can develop when photographic film is stored in warm, humid conditions. The gelatin image carrying emulsion provides an ideal food source for the mould. The resulting damage can cause partial or serious irreversible damage to the film's image layer.

Preserving our motion picture film holdings

Preservation action

Films are removed from their original canister and examined on a film winding bench to assess condition, technical details and pictorial content. Damage and deterioration are generally found to be due to poor storage, mishandling or frequent use prior to being transferred to the Archives.

Duplicating and digitising

When making the decision to copy a film a number of factors are considered. Is the film unique; is it the best available copy; does the film contain unique Australian footage; is the film of special significance; is it at risk of further deterioration, even in specialised storage? Sometimes we duplicate films of particular significance to film. However, we usually digitise film content to produce both preservation and access digital files. This strategy enables us to preserve the original record in long-term storage and make the digitised content accessible.

Treatment and repackaging

Films receive basic preservation treatment, including attachment of new film leader to both ends and winding at a low-tension, preservation wind as flat as possible onto a film core. Films may also be repackaged into new archival polypropylene canisters. We transfer any information on the original canister label to the new canister.

The Archives intensively treats films chosen for copying. This treatment includes specialised solvent or mechanical cleaning and repair of mechanical damage such as tears, broken splices and perforation damage. While scratches on films are irreversible, careful cleaning will minimise the likelihood of further damage from dust and grit.

Storage

Once films have been treated or copied, they are wound onto film cores with a low-tension wind before they are packaged in vented, acid-free plastic cans and stored in temperature and humidity-controlled conditions. The Archives has specially designed temperature and humidity-controlled storage facilities for long-term film preservation.

Copyright National Archives of Australia 2017