Photographic materials.

Photographical materials are nowadays more and more integrated in library and archival collections. As photographic material we consider following media:

• Photographs
• Negatives and slides
• Glass-plates
• Microforms and microfilms
• Moviefilm

The process of making photographs is mainly based on chemical processes which occur in an emulsion layer. For a better understanding of the processes, the components of photographic material should be known.

Photographs as we know them are mainly composed of 2 or 3 components. The basic components are:

• A basematerial that acts as a support and which can be rigid or flexible.
  
  • Rigid supports were mainly used in former times and include glass and metals and exceptionally ivory, wood,
    etc...
  • Flexible materials include paper (which is opaque) and different transparant plastic materials such as nitrocellulose, cellulose-esters and polyester.
    
    
• An emulsion layer which is a mix of a binder, such as gelatine, albumine or collodion (depending on the timeframe one considers) and imageforming elements of which the most common and bestknow are silverhalides.
  
  
• Sometimes an intermediate layer between support and emulsion layer is used, which is smooth, white and not transparent. A musch used intermediate layer was barytapaper.
  
  
  © De Zilveren Passer.
  

The preservation of photographic materials is being influenced by the stability of the support and the emulsion layer. This stability is being affected by temperature, humidity, light, UV-radiation, chemical pollutants and even ordinary use. The emulsion layer is the most vulnerable of the two, although bad manipulation and exposure of the support can also lead to deterioration.