A photographic image is formed by the action of light falling onto a base material that has been coated with a light-sensitive emulsion. This latent image may then be 'developed' and 'fixed' by further chemical processing. The emulsion coating in photographs is usually gelatine, which incorporates either silver halide salts to form black and white images, or dyes or pigments to form colour images. The base can be made from any material that can be coated with an emulsion, but the most common bases are paper and film:

• paper-based prints – either colour or black and white with a variety of emulsion types depending on the age of the material – these can be simple 'snapshots' to mounted presentation photographs to very large aerial survey shots
• negatives – reversed polarity images from which positive prints are produced, which can be colour or black and white, and in a range of sizes – early negatives were on glass but for most of the 20th century flexible film bases were used. Film-based negatives can be in either sheet or roll form. 
• transparencies or slides – positive images on a transparent film base, which requiring viewing with a back light source or projection system – the most common are 35 mm slides but other sizes are also used.

In the 150 years since photography was invented, a wide variety of base materials and emulsions have been used in photographic processes.

Historical photographs may be daguerreotypes, using copper sheets and mercury vapours, or albumen prints made on very thin papers with an emulsion derived from egg whites. Early photographs were also made with supports of glass and metal and collodion emulsions. In the late 1880s glass negatives were replaced by a clear plastic film made from cellulose nitrate. This was superseded in the 1930s by 'safety film' on cellulose diacetate base and again in the 1950s by cellulose triacetate. Triacetate is still used as a film base today in conjunction with polyester film, which was introduced in 1960.

All materials degrade over time. We cannot control this inevitable deterioration, but we can control how fast it happens. It is useful to know that certain materials are susceptible to deterioration in particular ways just because of their properties, and that other materials deteriorate as a result of particular environmental conditions.

A photographic image is produced because of the reactive nature of the chemicals present in the emulsion and the processing. This reactivity makes the photographic image very susceptible to deterioration from poor quality raw materials, packaging, processing, poor storage environment or pollution.

• Glass transparencies or negatives are fragile because of the nature and age of the glass. 
• Albums and mounted material are susceptible to the same intrinsic deterioration problems of other paper-based records – brittleness, discolouration and loss of adhesion in the mounts. 
• High humidity may promote mould growth, particularly in gelatine emulsions which provide an excellent nutrient for mould, while low humidity can cause the emulsion to crack and the support to become brittle. 
• Some photographs are very light sensitive, and can fade or darken with excessive light exposure. 
• Film or prints that have been poorly processed may develop instability of the base material and staining or bleaching of the image. 
• Film-based negatives can be badly damaged by exposure to dust, dirt and fingerprints, which spoil the image quality and may also act as a moisture absorbent and promote mould growth.

Nitrate and acetate film bases present particularly serious problems in collections of archival film. The degradation processes that arise in these types of film cannot be halted and ultimately lead to irretrievable image loss, sometimes over very short periods of time.

Nitrate film is classified as a hazardous substance as it can self-ignite in some circumstances and is difficult to extinguish once it starts to burn. It must be stored separately from other collection materials, in a designated area that firefighters can identify. As nitrate film deteriorates it produces nitric acid fumes which will damage other records stored in the vicinity and can cause health problems for staff working with the material.

Nitrate film was widely used before the 1940s and can be identified by the following characteristics:

• a sticky or greasy surface 
• a dark yellow or brown all over staining 
• a strong bitter or acrid smell

Cellulose acetate film is also known as 'safety film' because it was developed to avoid the high risks associated with nitrate film. It was widely used until the 1970s and is still commonly used in some photographic applications. Once acetate film starts to degrade it gives off acetic acid vapour, a type of deterioration commonly known as 'vinegar syndrome'. As the deterioration progresses the base material shrinks and the emulsion layer starts to warp and wrinkle. Acetate film includes both diacetate and triacetate bases. Triacetate is relatively more stable than diacetate, but it too may develop vinegar syndrome as it ages.

Acetate film was produced after the 1940s. Degrading acetate film can be identified by the following characteristics:

• a noticeable vinegar smell 
• the base is warped or wavy 
• the emulsion contains bubbles, wrinkles or crystalline deposits

As with any archival item, correct handling of photographs will aid in preserving them for as long as they are required.

• Handle with care.
• Use lint-free cotton gloves at all times when handling photographic material. 
• Labels and identification stamps should never be applied directly to photographic material. Identification should be on the packaging. Pencil or an appropriate pigment pen can be used on the border of slides. Never write on the back of photographic prints as this will damage the image. 
• Never use metal pins, staples, paper clips, rubber bands or adhesive tape with photographic materials. 
• Viewing equipment should be well-maintained and in a clean work environment.

The method of packaging photographs will depend on the particular material and the use for which it is required. Photos may be kept in reference albums, enclosures, boxes and folders. Very fragile items such as glass plates, daguerreotypes or large presentation prints may require customised packaging.

• Archival quality packaging which passes the Photographic Activity Test should be used for long-term storage. If plastics are used they should be polyester or polypropylene – PVC should not be used at all. Archival quality paper or board should be used for envelopes, files and boxes.
• Prints and negatives should be individually packed in bags or envelopes or placed in individual pockets in an album page. Loose material should be packed in small groups in archival files or folders and then boxed. If paper-based albums are used the support and boards should be of archival quality, with all pages interleaved and the images held by photo corners. 
• 'Magnetic' or self-adhesive albums should never be used. 
• Do not roll oversized material. Store it flat in drawers or in a folder or box. If you have rolled material, contact your local National Archives of Australia office for advice on flattening it. 
• Slides can be stored in slide boxes, albums or hanging files made of an appropriate material as for prints and negatives.
• X-rays should be treated as negative sheets and stored in archival envelopes or plastic sleeves and then boxed or held in file systems.

Photographic material should be stored in a clean, dark, climatically-controlled environment. Black and white material should be kept at 8–12°C and 30–40% relative humidity, and colour at less than 5°C and 30–40% relative humidity. Temporary records and reference copies can be stored under general archives standards of 18–22°C and 45–55% relative humidity.

Materials degrade quicker when exposed to ultraviolet light. Fluorescent tubes which are low in ultraviolet light should be used wherever possible in storage areas. Ultraviolet light can be easily measured with a light meter, and levels should not exceed 75µW/lumen. Lights should be turned off whenever possible. Storage areas should not have windows, but if they do they should be covered with curtains or blinds.

Insects and rodents once attracted to a records storage area may start eating the records, so:

• do not eat in storage areas
• keep surfaces (floors, tops of shelves) clean 
• bait regularly for rodents and fumigate annually for insects

Different photographic materials have different levels of stability and therefore different life expectancies. When photographic methods are used as a recording system, it is important that the quality of the format is appropriate for the purposes for which the photos will ultimately be required.

• Polaroid prints are ideal for quick, short-term retention images but should never be used as a permanent record. 
• 35 mm positive and negative 'domestic' films may be suitable as auxiliary material but are not generally classed as preservation quality. Larger format, or 'professional' quality films should be used for important images. 
• Film should be used well within the use-by date, otherwise image quality and colour rendition can be seriously affected. 
• For permanent-value records, film should always be processed to Australian or international standards. Professional film laboratories should be used, rather than rapid process minilabs which do not provide archival processing.

For frequently used or significant material, reference copies should be made. A master and a working copy should be produced. If multiple reference copies are required a duplicating copy is also recommended. Photographic material should not be photocopied as the UV light emitted by the copier can damage the image.

Original photographic material should only be exhibited under stringent environmental guidelines. Copy material should ideally be produced for display.

Please contact the Agency Service Centre if you require further advice on protecting and handling your photographic material.

Follow this link obtain this advice in PDF format.