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Section VII: Storage, handling and conservation

7.1 Film archives
7.2 The care of grooved recordings
7.3 Magnetic tape deterioration: recognition, recovery and prevention
7.4 Permanence, care, and handling of CDs including CD-ROM, Writable CD, and Kodak Photo CD
7.5 Preservation of audio and video materials in tropical countries
7.6 Data density versus data security: formats suitable for archival purposes
7.7 Strategies for the safeguarding of audio and video materials in the long term
7.8 Photographic conservation

 

7.1 Film archives

Henning Schou

1. STORAGE

1.1 Introduction

Old magnetic tape and film, especially cellulose nitrate and colour film, are among the most unstable materials kept in an audio-visual archive. Since each successive generation of copies involves a loss of quality (with the exception, perhaps, of digital recordings) the principle aim of preservation is to keep the preservation copy viable for as long as possible. In other words, to minimize the loss or deterioration of the images and sounds recorded on the preservation, or nitrate copy. This involves the storing of material in an appropriate environment. In addition it is necessary to control the access to and use of the material, to reduce the risk of damage.

1.2 External Factors Affecting the Stability of Materials

The main factors affecting the stability of cinematographic film in dark storage are temperature, relative humidity and chemical contaminants in the atmosphere. For magnetic tape, the main factors are temperature, absolute humidity, dust and magnetic fields.

1.2.1 Air Purity

The air in many industrial areas contains small quantities of gases such as nitrogen oxide (also given off by nitrate film), sulphur dioxide, ozone (from photo copiers) and hydrogen sulphide. It is important, therefore, that a vault for archival storage of film is located where the air is clean or else the air supplied to the storage area is purified and filtered to remove gases and dust.

1.3 Storage Conditions for Cellulose Nitrate

The rate of decomposition of cellulose nitrate roughly doubles with every 6EC increase in temperature. Stores, therefore, need to be kept as cold as possible. Moderate relative humidity is also necessary to prevent the nitrogen dioxide gas given off during the deterioration of the film from reacting with the water in the atmosphere and in the photographic emulsion to form an acid that attacks the film.

The main factors affecting the stability of cinematographic film in dark storage are temperature, relative humidity and chemical contaminants in the atmosphere. For magnetic tape, the main factors are temperature, absolute humidity, dust and magnetic fields.

The FIAF Preservation Commission recommends the following storage conditions:

a. Storage Temperature

- 4EC (39EF) +/-1EC on a daily basis
- 4EC (39EF) +/-2EC on an annual basis

b. Relative Humidity

- 50% +/-2% on a daily basis
- 50% +/-5% on an annual basis
- Maximum Range: 40-60% RH

c. Rate of Fresh Air Intake

The rate of fresh air intake should be such as to permit a complete airchange over a period of 5 hours at 4EC. An empirical guideline is if the nitrate can be smelt, the rate of air change should be increased.

If the storage temperature is reduced by 6EC, the production of nitrogen dioxide will be reduced by approximately 50%, ie. by lowering the temperature from 24EC to 4EC, the amount of nitrogen dioxide is reduced to less than one tenth of the amount produced at 24EC. This means that, if the temperature is lowered, the rate of fresh air intake can be greatly reduced.

Nitrate films must always be stored away from other materials because of the fire hazard and the danger of damage caused by the nitrogen dioxide formed during the nitrate decomposition.

It is essential to be aware of, and to adhere to, the legal regulations and fire codes for the storage and use of cellulose nitrate film. The most important of these rules is that nitrate stores must be located at least 200 metres from the nearest accommodation and work areas.

1.4 Storage Conditions for Black and White Safety Film and Magnetic Tapes

a. Recommended Storage Temperature

- Less than
-
16EC (61EF).+/-1EC on a daily basis
-
16EC (61EF) +/-2EC on an annual basis

b. Recommended Relative Humidity

- 35% +/-2% on a daily basis
-
35% +/-5% on an annual basis
-
Maximum Range: 30-60% RH for film
-
20-50% RH for magnetic tape

c. Rate of Fresh Air Intake

- As specified by local health regulations.

Magnetic tapes must not be stored in the vicinity of stray magnetic fields.

1.5 Storage Conditions for Colour and Diacetate Films

a. Recommended Storage Temperature

-5EC (23EF) +/-1EC on a daily basis
-5EC (23EF) +/-2EC on an annual basis

b. Recommended Relative Humidity

30% +/- 2% on a daily basis
30% +/- 5% on an annual basis

- Maximum Range: 15-35% RH

c. Rate of Fresh Air Intake

- As specified by local health regulations

Archivists should not be disheartened by the low temperatures recommended above but should always keep in mind that every degree that the temperature is lowered is beneficial. It must be remembered that each 6EC increase in temperature halves the life of the material.

1.6 General Rules for Storage

a. General

As a general rule, safety motion picture film should be stored at a moderate relative humidity and at as low a temperature as the archive can afford. The relative humidity and temperature must be kept as steady as possible. If the air conditioning plant is set at its lowest possible temperature setting, the result is likely to be a varying temperature. It is preferable to accept a slightly higher, but stable, relative humidity and temperature. The air conditioning should be provided by more than one unit to avoid a complete failure of the system in case of breakdown or repairs.

With storage at low temperatures, precautions must be taken to ensure that the dew point is not exceeded when the material is taken from the vault. This can be achieved by acclimatizing the films at a temperature and relative humidity between those of the vault and the work areas. The dew point is defined as the temperature at which moisture in the air would condense onto the film as water.

b. Storage in Hot and Humid Climates

In hot and humid climates, preservation of the film without air conditioning is impossible. Even cellulose acetate base degrades, becoming sticky and distorted. This is known as the "Vinegar Syndrome" because of the acetic acid, with its characteristic vinegar smell, formed during the decomposition. The emulsion layers can separate from the base during this process and render the film unusable. Another danger with high humidities above about 60% is growth of bacteria and mould.

c. Storage in Sealed Bags

The humidity problem can be greatly diminished by sealing stable safety film and magnetic tape in vapour tight bags. Sealing takes place after the materials have been stored at approximately 2OEC (68EF) and 30-50% RH until such time as the water content has stabilized. In hot and humid climates this can be achieved more easily by using the film conditioning apparatus, known as FICA, produced by the Swedish Film Institute. Acetate film must not be sealed in bags unless it is absolutely stable with no sign of decomposition. The acetic acid given off during the decomposition process will act as a catalyst and accelerate the decay of the film, especially if the acid is trapped in a sealed bag.

Stable diacetate film may benefit from sealing in vapour tight bags as this will reduce the evaporation of volatile plasticiser.

Wrapping of nitrate film or sealing in plastic bags is detrimental to the film. It is important that the decomposition gases be allowed to escape otherwise it will lead to an acceleration of the rate of disintegration of the film.

1.7 Storage Rules

1.7.1 Location

As mentioned above, nitrate and acetate materials must be stored in different buildings because of the flammability and instability of nitrate and because of the detrimental effects of nitrogen dioxide. Whenever possible, preservation,1 duping and viewing copies of films should be stored separately to minimize the risk of losing all the copies of a film in a fire, flood or some other disaster. Even separation by a fire rated wall is better than no separation at all.

1.7.2 Method of Storage

The method of storage is also important since, in long term storage, various stresses and strains can develop in the material. The FIAF Preservation Commission have formulated a number of rules about the packing and storage of preservation copies of film and video tape. The most important of these are given below:

a. Collection material must not be stored on the floor.
b. Film cans should be stored horizontally in stacks no higher than 300mm (1 foot) and, where possible, all the cans should be of the same size.
c. Video tape should be stored upright on shelves with the winding axes horizontal. Video tapes should not be stacked on top of one another.
d. The containers should contain

i. one film and a core or spool only, or
ii. one video tape

No other material, such as paper and household plastic bags, should be placed in the containers. In some cases it may be desirable to enclose the film in special vapour-tight bags. The risk of problems from the vinegar syndrome must, however, be considered.

e. Cans for nitrate films should have one or more holes in the side, preferably towards the bottom, to permit the escape of decomposition gases.

Storage areas are expensive and maximum use can be made of them by installing mobile shelving units. These run on rails that should be installed flush with the floor. The second best option is standard fixed metal shelving.

1.7.3 Cyclical Maintenance

Every few years, it is essential to rewind and examine each reel of film to monitor its condition. Magnetic audio tape should also be spooled through at regular intervals to avoid print through, ie. the unwanted transfer of the signal on a tape to the layers that it is in contact with. The Ampex Corporation recommends that video tape be rewound every three years. There is, however, no widely accepted practice and few archives have sufficient staff to implement such routine procedures consistently. An inspection of a sample of the material is better than no inspection at all.

1.7.4 The Need for Correct Handling

It should be stressed that all the above points are worthless if the material is damaged by excessive handling. The content of a film of permanent value should only be accessible by means of a viewing copy and by striking prints from a duping copy of the original.

1.8 Storage Buildings

Sophisticated film and magnetic tape storage buildings are expensive, not only to construct but also to operate. Small archives may, therefore, have to find suitable accommodation that falls within their budget. Possible alternatives for acetate film include air conditioned office space or well insulated rooms. Unused ammunition storage depots, old underground shelters, caves or unused mines could be suitable for both nitrate and acetate film as well as for magnetic materials. The risk of fire and the general safety of the staff must, of course, be a major consideration when assessing the suitability of such sites.

In making these decisions, the cost of purpose built facilities, the cost of the installation and maintenance of air conditioning and the cost of the general administration etc. of a fully equipped archive must be set against the financial, moral, cultural and scientific consequences of the loss of important and irreplaceable audio-visual documents.

Other considerations include, for example, the possible frequency of cuts in the public electricity supplies. If cuts are frequent and the archive cannot afford suitable generating equipment to provide back-up power for the air conditioning, then it may be better not to provide air conditioning at all but to rely on good thermal insulation to hold the vault temperature as stable as possible. Dehumidifiers can be installed to remove excess moisture from the air. Variable temperature and humidity causes more damage to film than a higher than ideal, but stable, climate.

The archive should also examine traditional cooling methods used in existing buildings in the area. These could provide a generous flow of cooling, outside air past, and often through, the structure.

The design of a sophisticated film and magnetic tape store is quite complex. It will have specially designed and constructed buildings, air conditioning equipment, insulated vaults of various sizes and environments, loading areas and rooms for acclimatizing material before and, especially, after storage. It will possess fire extinguishing equipment water, carbon dioxide or some other inert gas system, such as those using halogenated hydrocarbons. It will have several alarm systems to warn of fire, air conditioning malfunctions and illegal intrusion. In addition it will have special facilities for the storage of cellulose nitrate film.

A nitrate film vault should be an isolated, purpose built depot exclusively used for the storage of nitrate material. It should be a single story building that satisfies all fire and legal requirements, including rules about the standard of fire rating for the construction materials. The building should be partitioned into fire resistant, concrete compartments, each of which should hold a maximum of 2,500 Kg (approximately 300,000m or 1,000,000ft) of nitrate film. The vaults should be as small as possible. Each vault should have doors opening outwards onto a corridor and be equipped with pressure vents to the outside. The depot should be fully air conditioned and the temperature and relative humidity should be continuously measured, recorded and monitored.

The fire alarm and extinguishing system should be as sophisticated as can be afforded. In the event of a fire, only local sprinklers in the burning vault or vaults should be activated to cool the walls to prevent the fire spreading. Water in vaults that are not burning would damage the remaining nitrate collection. The alarm system should warn not only of the outbreak of fire but of the malfunction of the air conditioning and of unauthorized entry to the storage areas.

Note 1: A viewing copy is one available for general access, ideally made from a duping copy kept specifically to make copies from. The duping copy is either a duplicate version of the preservation copy or is a copy made from the preservation copy. The preservation copy is the best preserved copy of the material held by the archive. It is only used if a new duping copy has to be made to replace a damaged or worn out one.


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