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. 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 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.