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

This paper describes the effects of accelerated artificial and natural ageing on samples of azurite paint tempera prepared according to traditional early Italian recipes. The pigment used was basic copper carbonate in the form known as azurite and this was mixed using whole egg tempera medium. Artificial and natural ageing of the dosimeters was performed using controlled ageing chambers and selected sites of varying environmental conditions. The effects of ageing were quantified using a number of analytical techniques, which include the following: thermal analysis (DSC and TGA), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The data were then compared with those obtained from samples which were naturally aged by exposure in selected European art galleries and historic castles for a period of 9 months. It was found that the changes observed on artificial light ageing alone were minimal. Mass spectrometry (DTMS) showed that samples had already undergone oxidation during the curing stage of 3 months [O.F. van den Brink, G.B. Eijkel, J.J. Boon, Thermochim. Acta 360 (2) (2000), this proceedings]. There were, however, measurable differences in the samples that had been subjected to thermal and pollutant ageing, and this was used to rank the sites.