Damage to photographs occurs in two ways: Through inherent instability in the materials and techniques, and/or as a result of interaction with the external environment. Although problems with materials and technique can sometimes be dealt with through conservation treatment, a good environment will slow down the rate of deterioration. Galleries and museums have strictly controlled environments in order to minimise damage to collections.
Inherent instability can take many forms, depending on the photographic materials and processes that have been used. Chemical residues are probably the most common cause of instability in both negatives and prints, usually due to poor processing, such as inadequate washing, and fixing; the image may either darken or fade as a result. Another example is compatibility between the emulsion and support layers. This is found in early resin coated papers, where the image layers may crack and flake. Plastic film supports such as cellulose diacetate film bases can shrink severely, causing the emulsion layer to distort, while cellulose nitrate film disintegrates rapidly and has been known to spontaneously combust.
Prolonged exposure to artificial or natural light can cause fading and tonal shifts in photographs; light damage is irreversible. Ultra-violet radiation, present in natural and fluorescent lighting is the most active and therefore the most damaging part of the spectrum. Infra-red radiation present in both daylight and tungsten light is a source of heat, posing another form of danger for photographs. Colour photographs, historic black-and-white photographs and modern black-and-white photographs all have different levels of resistance to light. Those most susceptible to light are early processes such as salted paper prints and albumen prints; the organic dyes used in colour prints are also particularly vulnerable.
• Display photographs in low light levels, well away from windows and strong light sources. The recommended museum light level is 50 lux.
• Reduce light levels by drawing the curtains during the brightest part of the day. Prevent sunlight from falling directly on works. Install UV filters on fluorescent tubes. Never spotlight a photograph.
• UV filters can be used on windows and glazing in frames.
• Have professional copies made of irreplaceable photographs and negatives. Display the copies and store the original material in a dark place.
Relative humidity and temperature
The amount of moisture in the air is in direct correlation to its temperature, the warmer the air the more moisture it can hold. Conversely, in cold conditions moisture can be deposited as condensation. High temperatures and humidity will accelerate chemical deterioration and encourage mould growth, particularly on gelatine-based material. Gelatine layers can also swell and become sticky. Low humidity can cause desiccation of emulsion layers. Constant fluctuations in temperature and humidity constitute the most damaging scenario, setting up a cycle of expansion and contraction in the various layers of the photograph, which can lead to severe physical damage such as distorted supports and flaking images.
• Display and store photographs in a cool, dry environment. The recommended museums levels are 20ºC and 50%RH.
• Try to avoid marked fluctuations in temperature and humidity – hang framed photographs on inside walls, well away from direct sources of heat such as fires and radiators.
• External walls tend to be damper. A stopper placed behind a framed work, at each corner, will allow air circulation and reduce the risk of mould growth.
• Avoid hanging photographs on walls in close proximity to kitchens and bathrooms. Never be tempted to store photographs in places like attics and garages.
Dust, insects and pollutants
Both gelatine and paper are particularly attractive food sources for insects, and most insect activity will thrive in an undisturbed, dusty environment. Dust, in addition to being abrasive, may also harbour chemical pollutants. Particulate silver, the ubiquitous photographic image-forming material both the nineteenth and twentieth centuries, will react dramatically to atmospheric contaminants such as hydrogen sulphide and peroxides. These are common not only in city environments, but in poor quality display and storage materials, wooden storage furniture, paints and varnishes. Visible deterioration of the photograph or negative will manifest itself as tarnishing in darker image areas (silvering out), changes in image tone from black to brown (sulphiding) and overall fading.
• Keep photographs in a clean, dust-free environment. Inspect stored material regularly for signs of insect activity or other damage. Isolate any suspect material from the rest of the collection.
• Restrict dust, insects and pollutants by using well-made storage boxes and frames that provide a good seal against the environment.
• Always use framing and storage materials that pass the ANSI PAT standard (American National Standards Institute, Photographic Activity Test). Consult a conservation materials supplier for details.
All photographs are vulnerable to mechanical damage. Glass supports can be cracked or broken, paper supports torn and creased. Fingerprints can leave a greasy residue which, in time, becomes etched in the surface of the emulsion.
• Always handle photographic negatives and prints with care, by the edges, preferably using cotton gloves.
Extensive damage can result from the use of inappropriate storage materials. Chemical pollutants may be emitted by poor quality storage materials and furniture, such as PVC enclosures, adhesives, unsealed wooden drawers and shelves and freshly painted or varnished walls or furniture. Other material sometimes stored with photographs, like newspaper clippings, poor quality cardboard mounts, paper clips and rubber bands can also cause deterioration.
• Always use archival quality storage materials that pass the ANSI PAT.
• Archival quality filing enclosures for photographic negatives and prints must be made from chemically stable plastics such as polyethylene, polypropylene or polyester. Alternatively, if paper enclosures are used they must be acid-free, unbuffered, that is having a neutral pH level, and free from lignin, sulphur and peroxides. Boxes and albums should also be made from materials of the same standard.
• Store glass plate negatives in individual archival enclosures, upright in an acid-free box.
• Never store photographs with material such as newspaper clippings and poor quality paper or card.
• Always store original material separate from copies and copy negatives, to avoid total loss if the original is damaged or misplaced.
• Photographic prints in storage boxes should be placed in archival folders or interleaved with acid-free tissue.
• Always keep cased images and albums intact. Interleave historic photographic albums with archival tissue and store in an acid-free box. Cased images are also best stored in archival boxes.
• When making up new photograph albums choose an acid-free type. Use archival paper or mylar photocorners to secure the photographs. Alternatively retain the photograph with small diagonal corner slits in the album page. Avoid albums with poor quality, self-adhesive plastic pages.
Mounting and framing
Poor quality mounting and framing materials are one of the main causes of damage to photographs. Acidic woodpulp mounts and animal glue, often used for mounting photographs in the past can cause fading and discolouration of images, together with degradation of paper supports.
• Mounting and framing materials should be archival quality, acid-free, unbuffered, free from lignin, sulphur and peroxides and pass the ANSI PAT.
• The photograph should be attached to a backboard using mylar corners or archival paper corners. A window mount, hinged to the backboard, will separate the photograph from the glazing in the frame. Photographs can sometimes stick to glazing when in direct contact.
• The frame moulding should be sturdy enough to support the glazing, the mounted work and backboard. The frame should be sealed using brown gummed tape or similar.
• The glazing should be acrylic sheet or glass. A well-made frame will exclude dust and insects.
Never attempt to treat a damaged photograph yourself. Consult a conservator, who will be happy to provide advice and information.