The chemists of the Rijksmuseum and of theUniversity of Amsterdam they discovered and disclosed in a study published in July 2024 on Heritage Science how it did Rembrandta great Dutch painter and engraver of the seventeenth century, to create his famous details based on “gold varnish”. Using sophisticated spectroscopic techniques, the doctoral students Fréderique Broers and Nouchka de Keyser were in fact able to map the presence of pararealgar (a yellow mineral) and semi-amorphous (orange/red) pigments in a detail of his famous oil painting The night watchfrom 1642. The gold pigments in question show traces of arsenic sulfide mixed with colors: Rembrandt used this technique to paint the gold thread in the embroidered coat and the gold embroidery in the double sleeves of one of the two protagonists of the work, Lieutenant Willem van Ruytenburch, the central character of the painting alongside Captain Frans Banninck Cocq.
But this chemical compound is dangerous? It all depends on the doses: according to the Toxin and Toxin Target Database (T3DB) Arsenic sulfide would be very harmful if ingested or even just inhaled in certain doseswhich probably partly happened to Rembrandt and other painters of the time and which could cause depression of the central nervous system and damage to the bone marrow, lungs, liver and kidneys, with the risk of cancer. For comparison, 600 micrograms per kg of body weight of arsenic trioxide (a sulfide-like compound) are enough to bring an individual of average physical condition to death.
The discovery of the Rijksmuseum and the University of Amsterdam is not the only “dangerous” secret of the painting The night watch by Rembrandt. The project Operation Night Watchstarted in 2019 to unravel the mysteries of this masterpiece, has in fact brought to light other interesting elements, including the presence of other compounds of arsenic and sulfur in the clothes of Lieutenant Van Ruytenburch himself (as seen in X-ray fluorescence scanning). Given the findings, scholars have realized that artists active in Amsterdam in the 17th century had a much wider range of materials at their disposal than previously believed.
