Preventive conservation of photographs
Preventive conservation involves preserving works of art by controlling the environments in which they are displayed, stored and transported.
Environmental factors that contribute to the deterioration of photographs include: light, temperature and relative humidity; dust accumulation and insect activity; poor storage and display materials; and incorrect handling.
Deterioration of photographs is also influenced by the materials and techniques used to create them; this inherent instability can take many forms. A common cause of instability in photographs is from chemical residues, a result of poor processing such as inadequate washing and fixing. The image may either darken or fade as a result. Colour photographs with inherent instability problems may change tone, the entire image becoming more blue, red or yellow.
The inherent instability of photographs can be reduced by providing a good environment for photographs; preventive conservation measures will slow down the rate of deterioration. The Gallery’s Conservation Department addresses preventive conservation for photographs in many ways that can be applied more simply in the home for the preservation of photographic collections.
Exposure to artificial or natural light causes damage to photographic materials such as fading and tonal shifts, and can accelerate other deterioration processes. Light damage is irreversible and cumulative, and all types of photographs are vulnerable, but the most susceptible to light are salted paper prints, albumen silver prints, and colour prints.
It is best to display photographs at low light levels, away from strong light sources such as windows that do not have light-blocking curtains. The recommended light level for displaying photographs at the Gallery is 50 Lux; this is why galleries displaying photographs and other sensitive materials are more dimly lit than those containing paintings, ceramics or sculpture. The most damaging component of visible light – the high energy Ultraviolet (UV) content – is controlled by using incandescent lights instead of fluorescent tubes which have a higher UV output. UV filters are used in situations where low UV light sources cannot be used. In addition, UV-filtering acrylic glazing is generally used instead of glass for framing photographs. The overall display time for photographs at the Gallery is limited to three months every two years to reduce cumulative light damage.
Temperature and relative humidity
Throughout the areas where works of art are stored and displayed, temperature and relative humidity (% RH) are maintained at a stable level: generally 21oC and 50% RH. Temperature and RH are interdependent and fluctuations in either can lead to problems with photographs, such as distortion of the photographic support and cracking or flaking of the emulsion layer. High temperatures will accelerate chemical deterioration processes in photographic materials, and at high humidity levels, gelatin layers can swell and become sticky, and mould can develop. Low RH can also cause problems including embrittlement of the emulsion layers.
Mid-20th-century gelatin silver photograph with insect damage, surface accretions and staining, resulting from poor storage conditions and handling click to enlarge
Early 20th-century gelatin silver photograph with tarnishing or ‘silvering out’ in darker image areas from exposure to poor storage materials click to enlarge
Dust accumulation and insect activity
Dust collected on the surface of a photograph can cause abrasion and scratching and may also contain chemical pollutants that react adversely with materials in the photograph. Insects are attracted to dust as a food source, but paper and photographic emulsions are also attractive. Attack from silverfish, cockroaches and paper lice can result in a ‘grazing’ of the surface, and include accretions, losses and staining. Photographs are best protected from dust and insects by storing them in well-sealed archival boxes, by displaying them in frames that have a good seal and by monitoring and addressing any insect activity.
Storage and display materials
Accelerated deterioration can occur if photographs are stored and/or displayed with inappropriate materials. Chemical pollutants are emitted into the immediate environment from poor quality materials such as PVC enclosures and albums, adhesives, unsealed wooden furniture, and freshly painted or varnished walls and furniture. Other materials such as woollen fabric linings, poor quality tissue paper and acidic cardboard mounts also cause deterioration from the ‘offgassing’ of chemical pollutants. Particulate silver, the principal photographic image-forming material in both the 19th and 20th centuries, reacts dramatically to atmospheric contaminants such as hydrogen sulphide and peroxides. Visible deterioration of the photograph or negative will manifest as tarnishing in darker image areas (known as ‘silvering out’), changes in image tone from black to brown (‘sulphiding’) and overall fading. To avoid this, photographs should be mounted and framed or interleaved and stored with archival quality chemically stable acid-free plastics such as polyethylene, polypropylene or polyester. Archival paper products should be neutral pH, unbuffered and lignin, sulphur and peroxide free. One sure way to determine if something is archival quality is to check if the material passes the American National Standards Institute Photographic Activity Test (ANSI PAT).
All photographs can be physically damaged by careless handling, which may cause creases, tears, and losses. Sweat and oil from the skin deposited on photographs will also etch into the emulsion over time. This can be prevented by wearing clean cotton gloves or nitrile/rubber gloves and using acid-free paper triangles to hold the edges of photographic materials.