Dosimetry of paintings: determination of the degree of chemical change in museum-exposed test paintings by mass spectrometry

Painted works of art are constantly exposed to and affected by their environment. The chemical, mechanical and visual characteristics of paintings are subject to changes. The paintings themselves can be seen as dosimeters that integrate the effect of their environment. In the present research, mock paintings are used as dosimeters to integrate the overall effect of the museum environment on the paint in a given time span. Direct temperature resolved mass spectrometry (DTMS) and the multivariate technique of discriminant analysis are used to compare the chemical composition of mock paintings exposed in five different museums in Europe. Changes observed on laboratory-exposed (light, temperature and a mixture of nitrogen oxides and sulphur dioxide) dosimeters serve as the calibration set. The methodology applied to derive chemical information from the dosimeters is presented here. The results obtained on the exposed mock paintings show that the principle of paint-based dosimetry works. Other factors than light alone are found to play an important role in environment-induced deterioration.