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7.8 Photographic conservation
Susie Clark, Photographic Conservator. Brochure published by the National Preservation Office, the British Library, London, n.d.
Photographs are housed in libraries and archives all over the world, but photographic conservation is still a relatively new subject, particularly in the area of chemical treatment. It is usually possible to prolong the life of a photograph simply by good handling and housekeeping practices and by providing suitable storage conditions.
This leaflet provides guidelines on handling, storage and basic housekeeping techniques.
Ideally, a photograph should not be handled at all! Obviously this would defeat the purpose of an archive as a useful resource, but it is still possible to keep damage to a minimum with careful handling procedures.
* Always use clean hands for examining photographs, and preferably wear lintless cotton gloves to avoid leaving finger-prints and stains on photographs.
* Always work on a clean surface area. If necessary, cover the surface with cheap, plain paper such as unprinted newsprint, which can be changed as soon as it becomes dirty.
* Use two hands to hold the photograph and, if possible, support it with a piece of stiff card, especially if the photograph is fragile or brittle. Avoid touching the emulsion surface.
* Remove envelopes from negatives and not vice versa. If a photograph appears stuck in its container, do not attempt to remove it.
* Do not stack up loose prints and glass plate negatives - nothing should be placed on top of photographs.
* Do not attempt to flatten rolled or curled prints - this job is best left to the conservator.
* Support a photographic album with a book cradle, to protect its structure and with book snakes to hold the album open at the relevant page.
* Do not allow food and drink in the vicinity of valuable pictures. Sooner or later, an accident will happen. Prohibit smoking, too. Even short-term exposure to nicotine can cause staining.
* Avoid the use of ink, especially felt-tip pens. If photographs become at all damp, the ink may travel through to the image side, and the caption may eventually become illegible, as well as damaging the original. Use a soft pencil.
* Do not use adhesive tapes, staples, pins, metal paper clips and rubber bands.
* Supervise anyone who handles photographs, particularly new members of staff.
* Examine photographs in light which has been ultra-violet filtered.
* Wherever possible, give your client a copy print rather than the original material, to reduce damage to the original. Many photographic libraries and some archives already supply copy prints for reproduction as part of their service. Advise clients on sensible handling procedures to avoid constantly returning to the original negative to make new prints.
housekeeping the importance of good housekeeping is often overlooked, but it is one of the simplest and cheapest aspects of preservation.
* Keep the archive research and storage areas clean. Apart from the surface dirt, which can build up on archival objects, dust will also cause scratches and blemishes on films and prints.
* Check temperature and relative humidity regularly. Also check for signs of deterioration such as mould and insect or rodent attack. Damaged prints should be removed and stored separately to await conservation.
* Avoid storing archives in basements - they are prone to flooding.
* Never place photographs near a heat source, such as hot pipes, or hang them above a radiator. Do not place or store photographs in direct sunlight.
* Keep photographs out of freshly painted rooms and away from freshly painted objects for at least 2 weeks and preferably 4 weeks. Fresh paints may emit peroxides which can cause damage to photographs.
* Keep copying machines away from the collections. Ozone, produced by electrostatic copy machines, is very damaging.
* Do not allow photographs or their containers to come into contact with household cleaners containing ammonia or chlorine.
storage Many of the problems visible in photographic archives are a result of poor storage. Photographs are complex objects and poor storage can cause many stresses on the different components of a photograph
housing One common cause of deterioration in photographs is the housing in which they are enclosed. Unfortunately, many of the original enclosures for photographs were far from ideal. However, good quality conservation storage materials are now available in both paper/board and plastic.
1. have a high alpha-cellulose content (above 87%)
2. have a pH of 6.5-7.5.
3. have an undetectable, reducible sulphur content.
4. be free of lignin, pH buffers, metal particles, acid, peroxides and harmful sizing agents.
Silversafe photostore paper is made from 100% cotton fibre and is particularly suitable for photographic storage. It was developed in response to the concern of photographic conservators about traditional storage papers.
Plastic enclosures should be made from polyester such as 'Melinex' or 'Mylar,' uncoated polyethylene or uncoated cellulose triacetate. Plastics should be free of plasticiser, added to make them flexible, and the surface should not be glazed or coated. Chlorinated sheeting, namely polyvinyl chloride (PVC), should not be used. A variety of enclosures are available for storage and many firms will supply them custom-designed for special collections. Glass negatives are best stored vertically in neutral paper enclosures and then in boxes, preferably made from acid-free board, which will provide an extra buffer against acidic pollutants in the environment. Both black and white and colour film negatives, and transparencies, are best stored in polyester sleeves in photographic storage boxes, or in a hanging file system in metal cabinets.
Most prints, black and white or colour, are best stored in polyester sleeves with photographic conservation board as a support, if necessary. They should then be placed in conservation boxes or files. The exceptions are prints with delicate surfaces, such as flaking emulsion, or lifting pigments, which should be seen by a photographic conservator.
Early photographic albums are often in poor condition and will benefit from being wrapped in photographic conservation paper and being placed in an acid-free box.
Polyvinyl chloride plastics, glassine envelopes, mechanical wood pulp papers, Kraft papers and old photographic product boxes (although the latter may be of archival interest in themselves) are all unsuitable for photographic storage.
All filing cabinets should be made of metal with baked enamel finish. While old wood may be safe, new wood must be avoided, especially if it has been bleached or freshly painted.
an extra warning
Cellulose nitrate film, which was produced mainly between 1889 and 1939, (although some production continued until 1950), can be very dangerous. Any nitrate film in a collection should be isolated and removed to a cool, dry, well-ventilated area until it can be copied. Cellulose nitrate film is highly inflammable and may spontaneously ignite in certain conditions. The greatest risk is with large amounts of old, densely packed film. In this instance the ignition temperature may be as low as 48EC. and the film should not be placed near an external heat source. Once cellulose nitrate begins to burn, it produces gaseous products which catalyse further decomposition and affect surrounding materials. It can also continue to burn under water or carbon dioxide. Highly toxic fumes, as well as smoke and heat, are produced very quickly. It is also worth noting that if the archive buildings or contents are insured, the policy may prohibit the storage of cellulose nitrate film.
There are a number of environmental factors affecting the preservation of photographs: temperature, relative humidity, air purity and light.
Generally, photographic materials gain added protection by storage at low temperatures. The rate of most chemical reactions doubles if the temperature is raised by 10EC. Conversely, lowering the storage temperature considerably reduces the rate of deterioration. Cycling of temperature is particularly destructive because it causes expansion and contraction which occurs differentially in each layer of the photograph, giving rise to various kinds of physical damage. Daily cycling of more than 4EC should be avoided and the temperature should not rise above 21EC at any time. A storage temperature of 10-15EC is best for materials other than colour photographs and film. Colour materials require a much lower temperature, ideally 2EC. This may be practical for valuable material which is infrequently used. However, where constant access is needed, the temperature should still be maintained at the minimum needed for human comfort. Rapid changes in temperature should be avoided as condensation can occur when materials are taken from cold storage and placed in a warm, humid room.
Relative humidity is probably the most important environmental factor in photographic conservation. It is closely related to temperature. Low humidity may cause problems such as flaking and peeling emulsions, but most problems occur with high humidity. This may promote deterioration such as foxing of paper, mould growth and adhesion of the gelatin layers of adjacent photographs. Again, cycling is particularly damaging. A constant level of 35-40% is recommended for a collection of mixed photographic materials. Humidity levels should never rise above 65% as mould will begin to grow.
A number of chemicals present in the atmosphere are capable of oxidising image silver. These include peroxides, ozone, sulphur-containing compounds (such as sulphur oxides and hydrogen sulphide) and nitrogen oxide, all of which are present to some extent in the environment. Suggested maximum limits for gaseous pollutants are not more than 1µgm-3 for sulphur dioxide and nitrogen dioxide, while ozone should be reduced to trace levels (25µgm-3). Unfortunately, this can only be achieved by an air-conditioning system.
light and display
Resin-coated prints are not particularly light stable, but archivally processed silver gelatin prints are essentially stable at low light levels. However, long- term display should be avoided where possible for salted paper, albumen prints and various non-silver pigment prints. Colour materials are particularly vulnerable to light in the presence of oxygen and moisture. The ultra-violet light spectrum is the most damaging to photographic materials in general.
Obviously colour transparencies suffer particularly from light damage due to a relatively high level of exposure. To prolong the life of transparencies, projection should be kept to a minimum. Some transparencies have been shown to fade noticeably after 20 minutes exposure to a projector lamp. The type of transparency used should be carefully chosen. Some will retain their original colours longer under projection, whereas others will last longer in dark storage. Master copies should be of the latter category.
In storage and display areas, lights should be fitted with UV filters. Polymethyl methacrylate ("Perspex") rather than glass, provides a better protection against UV light where prints are to be displayed. A light level of 100 lux is the maximum recommended display level. The materials used for mounting display prints should conform to the same standards as storage materials.
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