Preserving motion picture film
Motion picture film consists of a clear plastic base coated with a thin layer of gelatin. This layer contains an image made from colour dyes, or in black and white film, very small particles of silver. Film also comes in a range of widths or 'gauges': 35 mm and 16 mm are professional formats and 8 mm is usually a domestic format. Historically, there are three common types of film base: cellulose nitrate, cellulose acetate and polyester.
- Cellulose nitrate-based motion picture film was widely used by filmmakers until the early 1950s, but is highly flammable.
- Cellulose acetate safety film base was used from the 1950s. It can be identified by the words, safety film imprinted on the film edge.
- Polyester-based motion picture film used widely in picture theatres to project films because of its strength and durability.
A number of different components are created to make a motion picture film and include: camera negative and reversal (positive) films; magnetic film soundtracks; optical soundtracks; projection or release prints with optical soundtrack stripes along the film edge.
All materials deteriorate over time and although it is inevitable, correct handling and care can slow it down.
Motion picture film is at risk of three types of deterioration: chemical decomposition, mechanical damage and biological degradation. The plastics used to make motion picture film are at risk from different types of chemical deterioration.
- Cellulose nitrate film is very unstable. It can react with moisture in the air to form nitric acid. As nitrate film deteriorates it develops a sticky or greasy surface, a dark yellow or brown all-over staining and a bitter or acrid smell. It can self-ignite if stored in a hot, humid environment and may be almost impossible to extinguish once it starts to burn.
- Cellulose triacetate film is vulnerable to 'vinegar syndrome', where the plastic reacts with water in the air to form acetic acid. This produces a vinegar smell, which gives the reaction its name. Vinegar syndrome-affected film shrinks, distorts so that the film will not lie flat. Extremely degraded film often develops a white powder on the edges. The image layer can crack and appear fragmented. Eventually, the film layers can stick together and become blocked. Once film reaches this stage there is no practical way to repair it.
- Polyester film is mechanically tough and chemically stable. However, the gelatin image layer is still susceptible to scratching and to the effects of mould.
Health and safety risks
Care should be taken when handling degraded nitrate and acetate -based film because both pose a health and safety threat. Nitrate-based film is highly flammable and classified as a hazardous material. It has an acrid smell when deteriorating and must be stored separately from other collection materials in a designated area that firefighters can identify. Vinegar syndrome affected acetate film has a characteristic smell of acetic acid. Exposure to these fumes can cause throat, eye and skin irritations. If you are aware of these odours leave the films in their closed canisters. For further advice contact the Agency Service Centre.
Preservation and storage
Motion picture film is fragile and must be handled with care to extend its useful life.
- Handle film by the edges, and avoid touching the emulsion which is easily damaged.
- Return films to their protective packaging when finished using them.
- To minimise the possibility of mechanical damage, ensure that all playback and recording equipment is clean and in good working order before using it. If you are unsure how to use replay equipment contact the Agency Service Centre.
- A roll of film should be wound tightly enough so that it doesn’t unravel, yet loose enough to allow some airflow. This will minimise the risk of film blocking due to vinegar syndrome.
- Store film in clean canisters to protect them from dust, dirt, pests and other contaminants. Plastic canisters are generally preferred to steel film canisters which are prone to rust.
- Ensure that film is free from dust, mould and other contaminants before enclosing it.
- A roll of film should be wound evenly onto a reel or core so that when it is stored in a film can it will be as flat as possible. The end should be secured with archival hold-down tape.
- Label every film can clearly and prominently for easy identification and to reduce handling.
Motion picture film is at particular risk of damage when being projected.
- Mishandling during winding or projection can tear film and cause old splices to fail.
- Improper film threading for projection can result in perforation damage.
- Contact with dirt or other contaminants can permanently scratch film.
Good film storage is the primary strategy for preservation.
Warm and humid conditions, as well as changing temperature and relative humidity levels can accelerate chemical deterioration and encourage mould growth. Mould can cause serious damage to both image and base emulsion layers of motion picture film. The colour dyes in film are likely to fade over time, especially when exposed to light, heat and humidity. Therefore, it's very important to store motion picture film in cool, dry and stable conditions to slow deterioration. Lights should be turned off when the storage area is not in use. If storage areas have windows they should be covered with curtains or blinds to eliminate light and reduce heating effects. Recommended conditions can be found at, Physical Storage of Commonwealth Records (page 34).
- Store motion picture film horizontally on powder-coated steel or wooden shelves, with an inert coating.
- Do not stack film cans more than five high and preferably less if they are 35mm films.
- Do not eat or leave food in storage areas as this can attract pests.
- The lowest shelves should be 15cm off the floor in case of minor flooding.
- Films should not be stored on the top of shelving units where they will be exposed to dust and the possibility of water damage from roof leaks.
Important and frequently used films should be digitised for preservation and reference purposes. Film digitisation specialists that undertake film to digital video file and film to DVD copying, (for access) are located throughout Australia. Contact details for these service providers may be found in local telephone directories.
Contact the Agency Service Centre.