Scientists unlock extra secrets and techniques of Rembrandt’s pigments in The Night Watch

Since 2019, researchers have been analyzing the chemical composition of the supplies used to create Rembrandt’s masterpiece, The Night Watch, as a part of the Rijksmuseum’s ongoing Operation Night Watch, dedicated to its long-term preservation. Chemists on the Rijksmuseum and the University of Amsterdam have now detected uncommon arsenic-based yellow and orange/purple pigments used to color the duff coat of one of many central figures within the portray, in line with a latest paper within the journal Heritage Science. It’s a brand new addition to Rembrandt’s identified pigment palette that additional provides to our rising physique of data in regards to the supplies he used.

As previously reported, previous analyses of Rembrandt’s work recognized many pigments the Dutch grasp utilized in his work, together with lead white, a number of ochres, bone black, vermilion, madder lake, azurite, ultramarine, yellow lake, and lead-tin yellow, amongst others. The artist hardly ever used pure blue or inexperienced pigments, with Belshazzar’s Feast being a notable exception. (The Rembrandt Database is the perfect useful resource for a complete chronicling of the numerous completely different investigative stories.)

Early final 12 months, the researchers at Operation Night Watch discovered uncommon traces of a compound known as lead formate within the portray—stunning in itself, however the workforce additionally recognized these formates in areas the place there was no lead pigment, white or yellow. It’s doable that lead formates disappear pretty shortly, which may clarify why they haven’t been detected in work by the Dutch Masters till now. But if that’s the case, why did not the lead formate disappear in The Night Watch? And the place did it come from within the first place?

Hoping to reply these questions, the workforce whipped up a mannequin of “cooked oils” from a Seventeenth-century recipe and analyzed these mannequin oils with synchrotron radiation. The outcomes supported their speculation that the oil used for mild components of the portray was handled with an alkaline lead drier. The incontrovertible fact that The Night Watch was revarnished with an oil-based varnish within the 18th century complicates issues, as this will have offered a recent supply of formic acid, such that completely different areas of the portray wealthy in lead formates might have shaped at completely different instances within the portray’s historical past.

Last December, the workforce turned their consideration to the preparatory layers utilized to the canvas. It’s identified that Rembrandt used a quartz-clay floor for The Night Watch—the primary time he had performed so, maybe as a result of the colossal dimension of the portray “motivated him to search for a less expensive, much less heavy and extra versatile various for the bottom layer” than the purple earth, lead white, and cerussite he was identified to make use of on earlier work.

They used 3D X-ray strategies to seize extra element, revealing the presence of an unknown (and sudden) lead-containing layer situated simply beneath the bottom layer. This might be as a consequence of utilizing a lead compound added to the oil used to organize the canvas as a drying additive—maybe to guard the portray from the damaging results of humidity. (Usually a glue sizing was used earlier than making use of the bottom layer.) The lead layer found final 12 months might be the rationale for the bizarre lead protrusions in areas of The Night Watch, since there are not any different lead-containing compounds within the paint. It’s doable that lead migrated into the portray’s floor layer from the lead-oil preparatory layer under.

An intentional mixture

The presence of arsenic sulfides in The Night Watch seems to be an intentional pigment mixture by Rembrandt, in line with the authors of this newest paper. Artists all through historical past have used naturally occurring orpiment and realgar, in addition to synthetic arsenic sulfide pigments, to get yellow, orange, and purple hues of their paints. Orpiment was additionally used for medicinal functions, in hair elimination lotions and oils, in wax seals, yellow ink, bookbinder inexperienced (combined with indigo), and for the remedy or coating of metals like silver.

But the usage of synthetic arsenic sulfides have hardly ever been reported in artworks, though they’re talked about in a number of artists’ treatises relationship again to the fifteenth century. Earlier work utilizing superior analytical strategies reminiscent of Raman spectroscopy and X-ray powder diffraction revealed that Rembrandt used arsenic sulfide pigments (synthetic orpiment) in two late work: The Jewish Bride (c 1665) and The Man in a Red Cap (c 1665).

For this newest work, Nouchka De Keyser of the Rijksmuseum and co-authors used macroscopic X-ray fluorescence imaging to map The Night Watch, which revealed the presence of arsenic and sulfur within the doublet sleeves and embroidered buff coat worn by Lt. Willem Van Ruytenburch, i.e., the central determine to the fitting of Captain Frans Bannick Cocq within the portray. The researchers initially assumed that this was as a consequence of Rembrandt’s use of orpiment for yellow hues and realgar for purple hues.

To be taught extra, they took tiny samples and analyzed them with mild microscopy, micro-Raman spectroscopy, electron microscopy, and X-ray powder diffraction. They discovered the yellow particles have been truly pararealgar whereas the orange to purple particles have been semi-amorphous pararealgar. These are extra uncommon arsenic sulfide elements, usually related to degradation merchandise from both the pure minerals or their synthetic equivalents as they age.

But De Keyser et al. concluded that the presence of those elements was truly an intentional combination, based mostly on their perusal of a number of historic sources and catalogs of assortment cupboards with lengthy lists of assorted arsenic sulfides. There was clearly up to date information of manipulating each pure and synthetic arsenic sulfides to get completely different shades of yellow, orange, and purple.

They additionally discovered vermilion and lead-tin yellow within the paint combination; Rembrandt was identified to make use of these so as to add brightness and depth to his work. In the case of The Night Watch, “Rembrandt clearly aimed for a shiny orange tone with a excessive colour energy that allowed him to create an phantasm of the gold thread embroidery in Van Ruytenburch’s costume,” the authors wrote. “The synthetic orange to purple arsenic sulfide may need provided completely different optical and rheological paint properties as in comparison with the mineral type of orpiment and realgar.”

In addition, the workforce examined paint samples from completely different artists identified to make use of arsenic sulfides—whose works are additionally a part of the Rijksmuseum assortment—and located the same combination of pigments in a portray by Rembrandt’s up to date, Willem Kalf. “It is proof that a wide range of pure and synthetic arsenic sulfides have been manufactured and traded throughout Rembrandt’s time and have been obtainable in Amsterdam,” the authors wrote—most probably imported, for the reason that Dutch Republic didn’t have appreciable mining sources.

DOI: Heritage Science, 2024. 10.1186/s40494-024-01350-x  (About DOIs).