The research team that is analyzing the painting in Amsterdam has found that it was used to create the golden glow on the doublet of Lieutenant Willem van Ruytenburch, one of the main figures.
Rembrandt, the Dutch master of the Golden Age, mixed arsenic sulfide pigments in his most famous work, The Night Watch (1642). Research by the Rijksmuseum —which exhibits the painting— and the University of Amsterdam, which has been analyzing it since 2019, maintains that the artist thus created the illusion of a gold thread in the embroidery on the doublet of Lieutenant Willem van Ruytenburch. He is the figure dressed in yellow in the center of the painting, and Rembrandt used materials that arrived via European trade routes.
“We thought that Rembrandt had used natural arsenic sulphide pigments, such as orpiment (yellow) and realgar (red) for the gilding effect on Lieutenant van Ruytenburch’s gilt,” explains Fréderique Broers, one of the study’s lead authors, along with Nouchka de Keyser, over the phone. However, the application of high-tech spectroscopy, microscopy and X-ray techniques to two samples obtained in 2019 has revealed the presence of two other components. It was done during the so-called Operation Night Watch, and they found “pararealgar [formed as an alteration of realgar], for the yellow, and semi-amorphous pararealgar, for the orange/red. The second must have been obtained by heating or roasting the first, achieving what we call artificial arsenic sulphide,” she says.
Although arsenical pigments were used in still lifes at the time for fruit and flowers, the discovery indicates that Rembrandt was innovative in using something else for portraits. The discovery adds colour to the painter’s palette and expands the range of materials that 17th-century artists in Amsterdam were thought to be able to obtain.
The research has been published in the journal Heritage Science, and Broers admits that the terminology can be somewhat confusing “because different names are used for each of the pigments over time and in different countries.” However, with the help of specific analytical techniques, “which can distinguish two molecules even if both only contain arsenic and sulphide, we have been able to differentiate them,” he says. The pigments were very toxic in powder form, although once mixed with linseed oil to obtain paint they were stabilised.
Realgar is often found in older paintings because realgar degrades into this compound over time, according to the expert. However, since it is distributed together with the semi-morphous realgar in a homogeneous and unaltered manner in The Night Watch, “we believe that the painter used them deliberately for its golden reflection effect on the lieutenant’s clothing,” says Broers. He wanted to recreate a luxurious fabric that would monopolize the light in the composition.
It is not clear whether Rembrandt bought the red and yellow mixture now discovered ready-made, or made it in his workshop.
Since the Netherlands does not have significant mineral resources, “we believe that they arrived via trade routes in Germany, Vienna and Venice, and the artist could buy them in Amsterdam,” says the work. Because of this, the use of natural and artificial arsenic sulfides may have been more common than previously believed in the Golden Age of Dutch painting. The artist did have vermilion, “which is mercury sulfide and also very toxic.” “And earth tones, obtained with iron.” The problem was that they lacked the depth of the mixture with the reddish and yellowish tones obtained with arsenic sulfide.
Cocq and Ruytenburch
The Night Watch is actually titled The Military Company of Captain Frans Banning Cocq and Lieutenant Willem van Ruytenburch. They are the two main figures in the group of arquebusiers who accompany them on their surveillance mission. The lieutenant “wears a brilliant outfit, possibly made of buffalo skin,” according to the Rijksmuseum’s documentation of the work. His sleeveless doublet “is magnificently decorated with dense gold thread embroidery,” and manages to be the centre of attention. Rembrandt was the first to depict figures doing something in a group portrait, and Captain Banning Cocq, dressed in black with a red sash, orders his lieutenant to start the company.
The artist and his 17th-century colleagues could consult manuals that explained the possible combinations of materials for painting and how to arrange the different layers. Although they were unaware of the details of the chemical reactions, “they knew, among other things, that arsenic sulfide should not be mixed directly with lead because it darkened the final effect.” The study includes a review of historical sources to trace the use of the pigments found, and notes something similar in a still life by Willem Kalf, a contemporary of Rembrandt and also resident in Amsterdam. This work belongs to the collection of the Rijksmuseum.
Since 2019, Operation Night Watch has uncovered some secrets of the famous painting. Rembrandt painted feathers on the helmet of one of the figures in the background, which were then erased. The change in the position of the leg of one of the portrayed people has also been seen; the reduction of the final number of spears; and an initial sketch of the final work, made on the canvas itself. The upper left-hand section of the canvas, which measures 3.79 x 4.53 metres in total, was also found to be warped due to the time it spent hanging in another room during the Rijksmuseum’s restoration work, which took place between 2003 and 2012. Lead was also found in a layer of impregnation spread beneath the ground used to prepare the canvas. The lead creates tiny protuberances that can come loose and damage the whole piece.
This will help to document and prepare for the conservation and cleaning of the painting, which owes its popular name to the yellowish varnish of its past. “For some time, it was believed that this type of coating added an authentic aspect to a Rembrandt masterpiece,” says Fréderique Broers. After the summer, the museum plans to provide information on the future of Operation Night Watch.
