Dosimetry of paintings: determination of the degree of chemical change in museum exposed test paintings (smalt tempera) by thermal analysis

One of the main concerns of conservators and curators is to find a method for evaluating the damage incurred by works of art in major galleries, historic houses, and castles with differing indoor environmental conditions. For this purpose, test tempera paintings were prepared and exposed at selected sites. The test paintings act as dosimeters and integrate the contributions from a range of factors which determine the overall environmental hazard to which paintings are exposed. Subsequent analysis of the test paintings involved an interdisciplinary approach using mass spectrometry (FOM Institute, the Netherlands), thermal analysis (Birkbeck College, UK) and non-invasive spectroscopic analysis (CNR–IROE, Italy). These techniques gave a measure of the physicochemical change and hence the resulting damage. In this paper, the thermoanalytical data will be presented, in particular of smalt tempera. Prior accelerated ageing of similar test paintings using controlled conditions was also performed to provide a comparison between artificial and natural ageing and a means for calibrating the test paintings.