Preserving photographs

What is a photograph?

A photograph is an image that is created by the action of light on a photosensitive paper or plastic substrate. Black-and-white images are formed by minute silver particles in a gelatin emulsion layer and colour images are formed by organic dye layers.

Prints

Traditional fibre-based photographic prints were based on high quality, pure cellulose papers and are considered to be an archival format. From the 1960s resin-coated paper (RC) prints were introduced because they could be quickly processed by hand or machine, but are not regarded as archival.

Negatives and transparencies

Photographic negatives and transparencies, (positive images) can be black and white or colour. Like other photographic formats they have a gelatin image layer.

Negatives are used to print positive images on photographic paper. They found in a range of sizes, the most common are: 35 mm, (miniature) and 6 cm (medium format) roll film; 4" x 5" (102 x 127 mm) and even bigger large format sheet film. Negatives were also produced on a glass base. These will most likely have been produced between the late 1890s and the 1950s.

Transparencies have a positive image and can be viewed directly or through a projector. They are usually colour images (35 mm slides) but can also be black-and-white (glass lantern slides) Transparencies can also be used to produce photographic prints.

Types of materials

Photography was commercially introduced in 1839. In Australia the earliest extant photographic images are from the mid-1840s. The earliest processes likely to be found in collections are daguerreotypes - mercury/silver image on silver-plated copper plate (1840s), ambrotypes – silver image on glass plate and albumen print – silver image on fine artist's papers (1850s).

Commercial colour processes date from the beginning of the 20th Century. However, it is likely the earliest colour photographs found in collections will be from the 1930s.

Preservation and storage

Photographs are prone to various types of deterioration that can affect both the image and support layers. The prime causes of deterioration in photographic materials are poor processing, atmospheric pollutants, physical fragility and chemical instability.

  • If chemicals are not thoroughly washed out during photographic image processing, then the residues can cause staining, darkening or fading over time. With good storage this deterioration will usually slow and it is advisable to create a copy when image deterioration is noted.
  • Pollutants can cause image discolouration and staining.
  • Generally, photographic materials should be held carefully by the edges. Glass supports can break if dropped and embrittle over time. Paper supports will tear and film negatives are prone to chemical deterioration. The image layer should never be touched with bare hands.
  • Black-and-white albumen prints will fade over time, particularly in high humidity.
  • Colour images change colour balance as they age. This is because one or more of the dyes that form the image becomes colourless. For example, colour images from the 1970s often appear orange, because the blue dye is starting to disappear.
  • In early resin-coated paper prints the polyethylene layer on the front and back of the photo may form an irreversible network of cracks.
  • Decorative cardboard mounts and album pages can yellow with age and stain photographic paper. They can also become brittle and if they break, the print is likely to break as well.
  • Cellulose nitrate and cellulose acetate film-base plastics are also inherently unstable.
  • While we cannot stop inherent deterioration – with good storage packaging and environments we can influence how fast it happens.

Cellulose nitrate and acetate films deteriorate irreversibly over time. Copying photographic images is a standard preservation strategy. However, where copying programs are not readily available, specialised low temperature and relative humidity storage will significantly slow deterioration and 'buy time'.

Nitrate film

Nitrate film was the first successful plastic film base, and was used widely from its introduction in 1889 until the early 1950s for motion picture and still film negatives. It has widely varying stability and is highly flammable. When cellulose nitrate deteriorates it releases distinct acrid vapours (nitrogen oxides) that are corrosive to various materials and a human health risk. The film sheet will deform and the surface can develop a greasy quality. In later stages dark yellow/brown staining develops, the film becomes sticky and the image bleaches out. The film finally disintegrates. Tightly wound motion picture film seems to deteriorate more readily.

Cellulose acetate film

Although cellulose acetate 'safety' film, was available in various forms from the 1920s it did not replace the unstable nitrate film base until the early 1950s. It is still used today for motion picture and still film negatives.

As acetate film deteriorates it releases acetic acid that gives it a vinegar smell (known as 'vinegar syndrome'). As deterioration progresses the film base shrinks and becomes brittle, eventually the emulsion layer buckles and separates from the base. It can also develop bubbles under the emulsion layer and white crystalline deposits on the surface.

Ideally, both nitrate and acetate negatives should be kept isolated from other collection material because of the damaging vapours they produce. Additionally, there are regulations that restrict the quantity of nitrate film that can be stored at a single location because of its flammability.

Storage

Ideally, agencies or institutions should store photographic collections in a dedicated space:

  • A storage area with stable climate control is recommended for important collections. Specific information can be found in the Standard for the Physical Storage of Commonwealth Records.
  • When these conditions can’t be maintained, aim for a stable environment and avoid high temperature and humidity levels. A cupboard in an internal room that does not contact external walls can help the buffer photographic records from daily temperature and humidity fluctuations. Lower floor levels in a building are usually cooler and more stable than upper levels. However, avoid damp areas such as basements.
  • Packaging will protect photographic materials from light and dust.
  • Turn off the lighting whenever storage areas are unoccupied.
  • Keep storage and work areas clean and free of food and drink.
  • Inspect the storage area regularly for insects, water leaks, structural damage or other events that may threaten the collection.

Handling and care

The following basic points should be kept in mind when handling photographic material:

  • Paper bases can be creased, folded or torn when in good condition and are even more vulnerable when they deteriorate.
  • Photographic material should be handled where possible in its protective enclosure. If it must be removed then it should be handled with great care by the edges. Clean disposable cotton or surgical-type gloves may be used. Fingerprints will corrode the silver in black-and-white images and cause colour dyes to change colour.
  • Don't apply identification labels or stamps directly to photographic material. Identification should be on the packaging or a piece of archival paper slipped into a sleeve/envelope with the photograph.
  • Pencil or an appropriate pigment pen can be used on the non-image border of slides. If an inscription must be written on a photograph, use a soft (2B) graphite pencil along an edge on the back of the print. Write on a firm surface with light pressure to avoid indentations in the paper. Pencil does not write well on resin-coated papers, so it is advisable to use a pen with permanent pigment-based ink only on the back, along one edge. Do not stack prints before the ink has completely dried, otherwise it can transfer to the front of an adjacent photograph and be very difficult to remove.
  • Never use metal pins, staples, paper clips, rubber bands or adhesive tape to secure photographic materials. Do not try to remove tapes and labels adhered to photographic materials without conservation advice. Removal may cause damage. Only remove rubber bands and metal fasteners when it can be done without damage.
  • Photographic material should always be handled in a clean work environment and all viewing equipment should be well-maintained.

The way a collection is used should determine the type of enclosure. If the material is going to be regularly accessed, clear plastic enclosures allow the photographs to be viewed without removing them from their sleeve. If the collection is infrequently accessed, paper envelopes may be the best choice as they act as a buffer for the photographic item.

Polyester is the most stable plastic for photographic storage. Polypropylene (PP) is a low cost and readily available alternative. Never use polyvinyl chloride (PVC) sleeves and folders.

Use paper envelopes that are known to be safe for photographic materials. The National Archives carries out a test known as the Photographic Activity Test (PAT) to determine the suitability of materials for the storage of photographs. Photographic collections require higher quality paper than paper-based collections: 'acid-free' does not necessarily mean 'photo-safe'.

Never use 'magnetic' self-adhesive albums because, over time they can cause severe damage to your precious photographs.

If photographs are stored in a display album ensure that it is manufactured from 'photo-safe' materials. The National Archives tested a number of commercially available albums and found them acceptable for storage of photographic materials. For specific information see the photographic activity test.

Colour photographic slides can be stored in their original plastic boxes. Otherwise, they can be stored in archival quality slide storage pages available from photographic retailers and conservation suppliers. Slide storage pages should have passed the photographic activity test.

Further advice

Contact the Agency Service Centre.

Copyright National Archives of Australia 2014