The preservation of audio visual materials is a labour intensive and time consuming activity. Audio visual records are most often motion picture film, video tape and digital video files although at Archives New Zealand we also preserve audio cassette and slide sets and film strips.
Pre-1951 motion picture film was produced using cellulose nitrate film. Nitrate film needs to be stored in special conditions and copied onto newer acetate film stock to prolong its life. If stored in bad conditions it can decompose to a point where the image and sound can no longer be recovered. Archives New Zealand has approximately 2000 cans of nitrate film and there is a continuing programme of copying all of our nitrate film onto safety film to ensure its long term preservation. We also wind through our entire nitrate collection yearly to monitor any decomposition.
Left: A badly decomposed nitrate film. The acids given off also corrode the metal can.
Right: One of our vaults with the preservation copies of our nitrate collection.
In the early 1950’s nitrate film was replaced with a less unstable alternative, cellulose acetate. Although acetate film proved to be less flammable than nitrate film it also suffered from decomposition. When acetate film decomposes it gives off strong acetic acid (vinegar) gasses giving it the common name ‘vinegar syndrome’. The gasses given off by decomposing film can also start other films to decompose and so have to be separated from the rest of the collection.
As with the nitrate film, when an acetate film begins to decompose we copy it onto new stock and store it in the correct conditions.
An acetate magnetic sound track with vinegar syndrome. As it decomposes it goes limp with crystals forming on it. The gasses given off were so strong they began to melt the plastic can.
Both nitrate and acetate decomposition affects the base of the film. Another issue which affects motion picture film is the fading of the image element. This is most often seen in the picture turning red. The reddening of the picture is caused by the colour dyes in the film’s emulsion decomposing leaving only the red colour dye. As the colour fading sets in it is harder and harder to correct that colour either in the laboratory or when copying on video tape.
Videotapes where first used in television in the late 1950’s and like film the physical tape is susceptible to decomposition and the audio visual information is susceptible to damage and information loss. What also makes video difficult to preserve for long periods of time is the support of the machines that bring the image and sound back together from the video tape. Older video machines are hard to find and hard to maintain and there are also multiple formats and systems, some of which were used widely and others which were only used for small periods of time or by specific organisations.
Some of the various video formats Archives New Zealand has to preserve: 1 inch, 2 inch, U-Matic and Beta SP.
To ensure that all of our audio visual holdings are preserved and ensure their long term survival and access we store all of our audio visual material storage in conditions that retard decomposition and fading and have programmes of duplication and migration using processes that ensure the absolute minimum quality loss.