Unveiling Rembrandt’s use of red lake pigments in The Night Watch by bi-modal imaging spectroscopy approach

Over recent decades, efforts to reduce the taking of micro-samples have driven the development of non-invasive, macro-scale spectral imaging techniques. This approach was central to the research phase of Operation Night Watch, the extensive conservation project on Rembrandt’s The Night Watch (1642), combining macro-scale imaging techniques with targeted sample analysis before conservation treatments. Red lake pigments are a key component of Rembrandt’s palette and are widely found in the painting, and their analysis remains challenging. This study aims to map red lakes in The Night Watch using macro-scale X-ray fluorescence imaging spectroscopy (MA-XRF) and visible-to-near-infrared reflectance imaging spectroscopy (RIS-VNIR), and to determine whether they were applied as glazes over or mixed with vermilion. Principal component analysis (PCA) of selected RIS-VNIR spectra, supported by paint models and cross-section comparisons, demonstrates that the red lake application method can be determined from RIS, and the results offer insights into Rembrandt’s artistic choices.