Contributions to the 5th AICCM Book, Paper and Photographic Materials Symposium. Editors: Prue McKay and Alana Treasure. Canberra, ACT: AICCM (Inc.), 2008.
This presentation examines the mechanisms of silver image fade in cellulose nitrate motion picture film and describes a non-chemical treatment to intensify the faded silver image. From the earliest days of motion pictures until the early 1950s, cellulose nitrate was the dominant polymer used for professional motion picture film base. In the presence of moisture, cellulose nitrate decomposes via a hydrolytic pathway and releases a range of nitrogen oxides, some of which combine with moisture to form nitrous and nitric acids. The first stages of decomposition include the fading or yellowing of the silver image to colourless silver compounds, due to oxidation effected by the nitrogen oxides. Traditional techniques for intensifying a silver image involve aqueous solutions. However, the gelatin emulsion of a decomposing film is not sufficiently stable to withstand the treatment and will generally disintegrate if it is exposed to aqueous solutions. An alternative technique is the vacuum pre-treatment and exposure of the film to specific wavelengths of light, thereby reducing the silver compounds to metallic silver and substantially reforming the original image.