Preserving motion picture film
Film is made from a clear plastic base and a thin gelatin emulsion layer. The gelatin contains an image made from colour dyes. In black and white films, the gelatin contains very small silver particles.
Film bases come in three types:
- cellulose nitrate
- cellulose acetate
- polyester
Film also comes in a range of widths or 'gauges'.
Most films within our collection are 16mm and 35mm gauge cellulose acetate-based. We have some 8mm acetate films and some 35mm cellulose nitrate films. We also have many 16mm and 35mm polyester films.
Three types of problems affect motion picture films:
- chemical decomposition
- mechanical damage
- biological degradation
While these factors drive our approach to film preservation, they are not our only challenges.
We must maintain the equipment needed to repair, clean or view films. This equipment is mostly obsolete in the wider film industry and as such, harder to get or maintain.
Another challenge is ensuring we're effectively using the latest technology in order to preserve our films and provide access.
Chemical decomposition
There are 3 main motion picture film bases that are at chemical decomposition risk.
Cellulose nitrate
This film base is very unstable. It can react with humidity to form nitric acid. As it ages, nitrate film develops a sticky or greasy surface, a dark yellow or brown all-over staining, and a strong bitter or acrid smell. It's also highly flammable, so we store it in special fire-proof cabinets.
Cellulose nitrate film was only produced as 35mm film and used until the early 1950s. It is still found in collections, although there are only small quantities in our holdings.
Cellulose acetate
Cellulose acetate is known as safety film. It's more stable than cellulose nitrate. Over long periods, the film can shrink and become brittle as it reacts with humidity to create acetic acid.
This reaction is called 'vinegar syndrome' because the film develops a characteristic vinegar odour. Most of our holdings contain 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 due to its physical toughness.
It decomposes over time, but does so at such a slow rate that it doesn't pose a preservation risk if stored at low temperatures.
Image loss
Colour motion picture film is prone to fading, no matter the base. Often, colour dye fade results in an overall magenta appearance but other colours can appear due to the film development process and brand.
Black and white film is a lot more stable. But in bad conditions the image can take on a silver mirror effect that can obscure the images a little. When cellulose nitrate-based film ages, it can cause the silver image to fade a lot.
Mechanical damage
Faulty equipment or incorrect projector threading can cause holes and breakages in motion picture films.
Cement or tape splices are used to edit and repair films. Old tape splices can age and fail.
Without careful handling, dirt or other contaminants can cause scratches in the delicate emulsion layer. When this happens, the damage can't be reversed.
Biological decay
Mould can grow when photographic film is stored in warm, humid conditions.
The gelatin image carrying emulsion provides an ideal food source for mould. This results in partial or serious damage to the film's image layer that can't be reversed.
Preserving our motion picture film records
We remove films from their original cans and examine them on a film winding bench. We do this to assess:
- condition
- technical details
- pictorial content
Poor storage, mishandling or frequent use before transfer to our collection is usually what speeds up damage and ageing.
Digitising motion picture film
When we decide to copy a film, we consider:
- Is the film unique?
- Is it the best available copy?
- Does the film contain unique Australian footage?
- Is the film especially significant?
- Is it at risk of further damage, even in the right storage?
We preserve film by digitising it on special scanners. We create a high-quality master file and a smaller access file. This lets us preserve the original record in long-term storage and make the digitised content available to researchers.
Treatment and repackaging
To preserve films we:
- attach a new film leader to both ends and wind at a low-tension
- wind them as flat as possible onto a film core to better preserve them
- repackage films into new archival polypropylene canisters
- transfer any information on the original canister label to the new canister
We intensively treat films we copy.
This includes:
- hand cleaning with specialised solvent
- cleaning mechanically in a purpose built machine
- hand repairing tears, broken splices and perforation damage
While scratches on films are set, careful cleaning will lessen further damage from dust and grit.
Storage
Once we complete treating or copying films we:
- wind them onto film cores with a low-tension wind
- package them in acid-free, archival-quality plastic cans
- store them in temperature and humidity-controlled conditions
We have specially designed temperature and humidity-controlled storage facilities to preserve films long-term.
