Since the 1830s photographic images have formed an integral part of our visual heritage recording historical events and social and family life. Photographs are composite objects consisting of the support layer, the emulsion layer and the image material made of silver particles in black and white images and synthetic dyes in colour images. Black and white photographs have a much more stable image than colour photographs. The complex physical and chemical structure of the photograph presents special storage and packaging needs to prolong the life of the photographic image. Correct handling practices also play an important part in the preservation of photographs.
Storage furniture, including cabinets and shelves, should be made of non-combustible and corrosion proof materials. Avoid storage furniture made of wood and wood by-products since they contain chemicals harmful to photographs. Allow air to circulate freely around the cupboards and shelving to avoid the build up of stagnant air pockets.
Store the photographs in an environment where temperature, humidity and light levels can be reasonably controlled. Storage conditions which are too warm and too damp will greatly accelerate the chemical and physical deterioration of the photograph. Keep photographs away from attics and basements and areas where there is a risk of fire or flood. High humidity and temperature promote chemical change in the photographic image; evidence of this is black and white images oxidising (silver particles tarnishing) and colour dyes shifting and fading. Low humidity causes photographic emulsions and support materials to crack and become brittle.
Temperature - Refrigeration is an affective method of storing colour photographs and film, however this is not always practicable. Also, if the material is not suitably protected there is the risk of exposure to high RH levels during cold storage and water condensation when brought out of cold storage. Alternatively, keep to a constant storage temperature of 5°C - 18°C for colour prints, black and white prints and film. Photographic material should not be exposed to any rapid changes in temperature and humidity either during storage or prior to viewing. If possible make provision for gradual acclimatisation to room temperature, which should be lowered again gradually after use.
Humidity - The optimum relative humidity level (RH) for a mixed photographic collection is 30 - 40%. This should be combined with low temperatures where possible.
N.B. A thermometer should be used for recording temperature and a hygrometer for RH levels.
Light - Materials used to create photographic images are never truly permanent and retain a certain level of light sensitivity. This means that continued exposure to light will ultimately result in the image fading. It is therefore important that daylight should be excluded from the storage area and use of artificial light should be kept to a minimum. Viewing time of photographic material should be kept short and viewing light levels kept low. The material should be covered if not immediately returned to storage 'after use. For display guidelines see displaying books and documents.
The use of protective packaging will not only provide physical protection to the photographic material but will also work as a barrier to atmospheric pollution and light.
Use commercially available packaging products specifically developed and tested for photographic storage; this means that they are free of substances harmful to photographs and film. Look for lignin-free and sulphur-free paper and board products. It is important to be aware that 'archival' and 'acid-free' products are not necessarily suitable for photographic storage. Do not use materials of unknown origin. Where possible, store similar materials and formats together.
- Paper prints (black and white and colour) - Use polyester sleeves for frequently viewed prints and store in good environmental conditions to avoid condensation inside the sleeve. Paper envelopes are used if viewing is infrequent and environmental conditions are poor. Use four-flap paper enclosures for photographs with broken or flaking emulsions. Large, oversized photographs need to be wrapped individually in large sheets of photographic conservation paper. Store flat or upright in suitable boxes taking care not to pack the photographs too tightly.
- Cased photographs (daguerreotypes and ambrotypes) - NO attempt must be made to remove the photograph from the frame. The frame is an integral part of the photograph and should be protected in storage. Wrap the cased photograph in archival photographic paper, slip into a paper envelope and box.
- Glass plate negatives - Place the glass plates in paper envelopes. Use four-flap paper enclosures for negatives with cracked and flaking emulsions. Store vertically in strong, rigid boxes and add a board divider at every fifth plate. This will cushion any accidental knocks to the box and its contents.
- Film negatives - Store negatives singly in paper envelopes or polyester sleeves for easy and frequent viewing and house in a suitable box.
- Slides - Store vertically in a suitable box designed to give full physical protection. Alternatively use polyester slide storage pages with individual pockets to fit ring binder files.
- Albums - Early albums should be wrapped in paper and placed into a fitted box. Photographs in heavily used albums should be copied to avoid damage to the binding. Photographs kept in modern albums should be removed and placed into archival albums now commercially available.
There is a full range of commercially available boxes designed specifically for the storage of photographic material.
There is always the risk of physical damage to unprotected photographic material through careless handling.
Follow these guidelines to minimise this risk.
- Always work on a clean work surface.
- Make sure that photographs are handled with clean hands. Never touch the emulsion side of the photographic image. If possible wear cotton lint-free gloves.
- Use both hands to support the photograph; alternatively, slide a clean piece of paper or thin card underneath and use as a carrier.
- Nothing should be placed on top of photographs: for example pens, pencils, keys.
- The use of photocopies can help towards solving some handling problems. However this must be carefully regulated as frequent photocopying can be harmful to the photograph. Do not attempt to photocopy rolled or curled photographs.
Duplicate copies and negatives should be kept in separate storage areas as security against possible fire or flood.
Remember to seek specialist advice if there is any doubt about the suitability of the storage accommodation or the appropriate protection methods and materials to be used.
A list of suppliers of materials and equipment is available.