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Preservation

Film and Videotape Preservation at the NRFTA

Film, videotape and digital data storage media are fragile objects which need care and expertise in the way they are stored and handled. They are both physically unstable (i.e. prone to chemical decomposition) and susceptible to damage in use.

Film

Film - a flexible, transparent material which is coated with a photosensitive substance to form the visible image - was first sold in roughly the form we know it today by the Eastman Kodak company in 1889. It was originally made from a base known as cellulose nitrate, which continued to be the base used in the professional film industry until the early 1950s. This had the advantage of being simple and cheap to manufacture and also having a very high tensile strength. However, nitrate has two major drawbacks. Firstly, it is a very dangerous and inflammable substance. Because nitrate film generates oxygen as part of the burning process, a burning reel of nitrate film cannot be extinguished. It will continue to burn even underwater! Burning nitrate also releases nitric acid fumes, which are extremely toxic. Inhaling these fumes will cause inflammation of the lungs and can be lethal. The other major drawback of nitrate is that over time it will decompose - eventually to the point at which the images and sounds recorded on it can no longer be recovered. Archivists have discovered that the decomposition process can be inhibited by storing nitrate in cool and dry conditions, hence the need for temperature and humidity-controlled vaults. But the only way of guaranteeing that the content of a nitrate film element will survive in the long term is to copy it, photographically, onto a more stable base.

A temperature and humidity-controlled vault at the NRFTA's Newcastle office.

Since 1909, acetic acid was substituted for nitric acid in an attempt to reduce the flammability of nitrate. These 'cellulose acetate' bases were used a lot in still and amateur movie photography from the 1920s onwards, but were rejected by the cinema industry because early forms of acetate were nowhere near as durable as nitrate. It wasn't until the invention of cellulose triacetate in 1948 that a so-called 'safety film' was available which almost matched the tensile strength of nitrate.Nitrate ceased to be manufactured in February 1950 (apart from in China and the USSR, which continued to use it on a limited scale until the mid-1960s). Whilst acetate does not have the fire risk of nitrate, it is still subject to decomposition. Deacetylation, or 'vinegar syndrome' as it is more commonly known, causes the film to shrink and become brittle over time, which again creates problems when trying to reproduce its content. Vinegar syndrome can also be inhibited by storage at a low temperature and humidity.

Since the late 1980s, most film stock has been produced on a polyester base. Being totally inorganic, this is not (it is believed) subject to the decomposition which has made nitrate and acetate so difficult to preserve, and is the base on which copies of nitrate and acetate originals are now made for long-term preservation.

A 16mm film element in the condition it would typically be acquired.

All film elements are given a thorough technical examination when they are acquired by the NRFTA. This determines what base they are on and whether there is any decomposition, colour dye fading or other damage. Films are cleaned where necessary and recanned before storage in an atmospherically controlled vault. If necesssary, they are sent to a lab where preservation copies are made.

After technical assessment and examination, the film is seen here ready for storage. It has been cleaned and repaired. The original container and spool in which it arrived has been replaced (after any information written on it has been carefully noted), as it was rusty and the spool was coated with a lacquer which can give off harmful fumes.

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Videotape

Mechanically, videotape is quite similar to film in that it consists of a flexible support onto which is coated the chemical substance that records the image and sound information. But there the similarities end. Videotape is a magnetic medium as distinct from a photographic one. On magnetic media, particles of magnetically sensitive material - known as the 'oxide' - are polarised by an electromagnetic source (the 'head' in a recorder or player) as they travel at a constant speed. In playback the process is reversed: the head generates energy in response to tape passing across its surface, which is then processed and amplified into the pictures and sounds you see on the screen.

This is a far more complicated process than the purely mechanical and optical means of reproducing moving images (and, to a certain extent, sound) from film. There have always been a very small number of film formats in existence (and two of them - 35mm and 16mm - account for almost 90% of the film stock ever made), and therefore an archive only needs to maintain a small number of machines in order to look after them. This is not the case with videotape. Since Ampex launched the first broadcast videotape system in 1956, which used 2" wide open-reel tape, there have been 20-30 formats in widespread use and as many again used for more specialist applications. The problem of 'format obsolescence' in videotape, therefore, is as big a problem as base decomposition in film.

This open-reel format uses videotape one inch wide, and was introduced in 1978. It was used extensively for high-quality studio recording until superceded by Betacam SP in the late 1980s. Though this sort of tape is generally very chemically stable, the machines needed to play and copy it are becoming ever more scarse. A highly-qualified engineer is needed to maintain them, and spare parts are becoming ever harder to come by.

UMatic was the first cassette-based videotape format to enter mainstream use, in 1971. A cassette - in which both the supply and take-up spool are housed within a self-contained mechanism - requires less technical skill to use than an open-reel format, and UMatic opened the way for a huge expansion in the use of videotape among broadcasters and in industrial/educational/promotional use during the 1970s. Because the tape was (for its time) very small, it tends to suffer a lot from oxide shedding off the surface of the tape, resulting in visible distortion, called 'dropouts' on the screen. As with one-inch 'C', equipment and spares are now very difficult to get hold of. The NRFTA holds approximately 5,000 tapes in this format.

One means of addressing the obsolescence issue is to copy tapes onto a newer format. But unlike the process of duplicating film for preservation, copying (analogue) videotape loses a lot more picture quality ('generational fading'), and it is likely that the new format will quickly become obsolete, too. Another potential solution is to copy analogue videotapes to a digital format, but that too has potential disadvantages (see below).

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Digital Media

In relation to moving image content, the term 'digital' describes the representation of images and sounds as numeric data encoded and reproduced by a computer. The data can be stored in a variety of ways: most digital video content is recorded on tape, but magnetic discs and optical discs read by a laser (e.g. DVDs) can also be used. Another way to record digital data is photographically, such as the digital sound recorded on film alongside the picture for playback in the cinema.

At first sight, digital technology is a very attractive archival medium because it does not suffer from the generational fading which happens when an analogue format, such as film, is copied. Just as long as you copy all the data accurately, you have a perfect clone of the original, capable of being played back to the same quality - so the theory goes. But this is a double-edged sword. Imperfections on an analogue source will appear as just that - for example, a scratch on film or a dropout on video. With a digital format, all the data has to be reproduced accurately in order to create any picture or sound at all. So whereas a slightly decomposed or damaged analogue recording can be played - albeit imperfectly - with digital, you'll either get a perfect picture or nothing at all. Furthermore, the use of compression (computer programs which reduce the amount of data needed to record images and sounds, such as are used, for example, in the recording and playback of DVDs) can degrade the technical quality of the signal, especially if it has to be decoded and then recompressed in a different format for preservation. An archivist, therefore, has to be very sure that the storage medium for digital data will not suffer from damage or decomposition before using it to preserve any collections.

Most digital storage media are just too new for us to know if they can offer long-term stability. Concern is being expressed in archive circles that the dyes used in recordable CDs and DVDs may not last very long, and digital magnetic tape formats are already showing some problems, especially in systems which use heavy data compression algorithms. The issue of how to preserve 'born digital' materials is one which the NRFTA, along with every other moving image archive, is rapidly having to think very seriously about.