IAQ 2003, Presentation 1:
Studies on the Susceptibility of Objects to Pollutant Gases
Susan Bradley & David Thickett
Atmospheric corrosion is a complex phenomenon involving the interaction of pollutant gases, relative humidity, temperature, dust and materials. Artefacts often have complex and heterogeneous compositions and do not react in a uniform way to their environment. The presence of soluble salts, corrosion products and conservation materials can dramatically alter an objects response to an environment. The combination of these factors leads to apparently similar objects having very different susceptibilities to their environment. Acetic acid is the most common, damaging, internally generated pollutant as a consequence of the use of wood and wood products in display and storage environments. Many surfaces will adsorb acetic acid and the porous structure of some substrates will also cause them to take up significant concentrations. The presence of acetic acid as acetate, or formic acid as formate on the surface of glass and enamel objects and in copper corrosion products have been detected instances using ion chromatography. Its presence is also ubiquitous in Egyptian limestone objects in certain storage situations, and cuneiform tablets stored in wood enclosures or cardboard boxes. Despite this, instances of deterioration involving acetic acid have been limited in the environment of the British Museum. When deterioration has been observed, it has been investigated, often from the perspective of a collection of objects in a common environment. The common themes of high relative humidity, wet treatment, and high temperature, and previous conservation treatments have run through this study. Preliminary conclusions regarding susceptibility are drawn.
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© November 2003