Publication Type:Conference Paper
Source:Works of art on paper: books, documents and photographs: techniques and conservation: contributions to the Baltimore Congress, 2-6 September 2002, ISBN: 0-9500525-7-4, p.65-68 (2002)
Keywords:air pollution, discoloration, humidity, opacity, paper (fiber product), transmitted light, ultraviolet radiation
Since 1998, the paper conservation department of the Instituto Português de Conservação e Restauro has been documenting works on paper which present partial or total discoloration and which do not fit the general pattern. The discoloration does not seem to be caused by light or water, but by prolonged contact with air. Visually this type of discoloration turns the paper more opaque and is not reversed by the usual treatments. In the research literature there is reference to photooxidation, foxing, \\"tidelines,\\" and other discoloration related to iron gall ink corrosion or from contact migration of unstable volatile organic materials, normally related to local high humidity absorption. Work on visual characterization, photographic documentation (UV and transmitted light) and simple analytical testing was carried out in order to support the empirical observation that the agent that caused the oxidation was air–the humidified and polluted air found inside a building. Parallel to this, tests were made with different oxidizing and reducing agents to reverse the opacity. The authors also discuss the reason the discoloration is accompanied by a loss of transparency.