The effects of organic pollutants on metals in museums: Corrosion products, synergistic effects and the influence of climatic parameters

The presence of indoor pollutants in museums is a fact and a real problem because they are quite difficult to keep under control. The use of new materials and techniques in the fabrication of showcases and, above all, the speed with which temporary exhibitions have to be opened, have brought new problems into the conservation field. Previous researches have tested metal coupons in an environment with high concentrations of pollutants (ppm) as well as high relative humidity (RH = 95-75%), but little is known on the effects of pollutants at low concentrations (ppb) and low RH. Considering that some materials are sold as low-emitting and the rush with which metallic objects are placed inside showcases after using them, low pollutant concentrations and short periods of time need to be tested. This paper presents a study of copper and lead coupons exposed to four polluted environments: low concentrations (100 ppb) of acetic acid, formic acid, formaldehyde and a mixture of Volatile Organic Compounds (VOCs) were created in environments of 54% RH for a short period of time (14 days and also 28 days for VOCs). Taking into account established pollutant limit values for objects in museums and their terminology, it was expected that little or no changes should be observed to the coupons. Nevertheless, it was found that in the case of lead, changes in the surface were observed, while in the case of copper, VOCs may have an inhibitory effect, which is something that will be studied in the near future. A discussion about limit values terminology is also provided, trying to elucidate which one should be used taking into account the results presented and being, above all, practical and realistic within museum environments