Sweden's medieval churches are often decorated with beautiful murals. Sometimes the authors are known, e.g. Albertus Pictor, Johannes Iwan or Johannes Rosenrod. Other times they are only named as "Egypticus", "The Master of the Passion", "The Master of Roslag" etc. The project team has previously identified about twenty different color pigments in these medieval paintings. However, we do not know where the pigments come from. Are they domestic or imported? Are they naturally occurring minerals or synthetic products? The planned investigations are limited to church paintings in Mälardalen, Skåne and Gotland. The composition of the pigments will first be determined using a scanning electron microscope. In cases where the pigments contain lead, the origin of the lead can often be established by determining the isotopic composition with a mass spectrometer. The values obtained constitute a 'fingerprint' that may be specific to a particular mine or region. Other pigments may contain metals such as copper, iron, cobalt, mercury, etc. In these cases, isotopic studies rarely provide any information about the origin, but we have to search the literature for probable medieval sites. Our interdisciplinary research group consists of natural scientists and conservators with backgrounds from the Swedish National Heritage Board, the Swedish Museum of Natural History, the Nordic Museum and Byggnadshyttan on Gotland. The results may therefore be of great interest to art historians, antiquarians, conservators, architects and mineralogists.