A multidisciplinary study of unusual red and blue lake pigments used in fifteenth-century Swedish wall paintings

This study aimed to understand and characterise previously unidentified fibrous red and blue pigments used in fifteenth-century wall paintings by Albertus Pictor in Härnevi church (Sweden). The findings demonstrate the importance of the synergy of material science, technical art history and conservation. The investigations enabled us to recommend a combination of analytical techniques to determine a clear and robust outcome for future researchers. Both pigments were investigated with optical microscopy, UV fluorescence microscopy, scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDX), and Fourier transform infrared spectroscopy (ATR-FTIR). The red pigment was further analysed with high-performance liquid chromatography (HPLC-DAD). Raman micro-spectroscopy was employed to analyse the blue pigment. Binding media analysis with nano-LC-ESI-Q-TOF was used to identify the binder in samples taken from the red area. Both pigments were found to be prepared from wool shearings dyed with madder for the red pigment and indigo (likely from woad) for the blue pigment.