How do you paint the color gold? It’s a question that comes up early for many artists, as soon as they’re drawing their first princess crown or dragon hoard and find that the yellow or brown crayons just don’t quite cut it. But even Rembrandt had this problem. His realistic paintings include intricate details, shadows and reflections and some even portray gold in a convincing way.
One of the central characters in Rembrandt’s large painting “The Night Watch” has detailed gold stitching on his outfit. The figure depicts lieutenant Willem van Ruytenburch, and he is one of the few lighter elements of this otherwise shadowy painting. (It’s not set at night, despite the name, but most of the group is out of direct light). The reflection of the light makes the gold on his clothes stand out even more.
Researchers at the Rijksmuseum and the University of Amsterdam have now discovered how Rembrandt deliberately altered paint pigments to create this gold effect. As part of a larger, extensive study of “The Night Watch”, they did an X-ray fluorescence scan of the entire painting, and also took small paint samples to look in more detail. The X-ray scan suggested that the section of the painting that showed Van Ruytenburch’s clothing included arsenic and sulfur, which hinted at the type of paint he might have used.
Under the microscopy, the “gold” paint was more clearly visible as specks of yellow and orange, and a chemical analysis identified it as two somewhat unusual arsenic sulfide components: pararealgar (yellow) and semi-amorphous pararealgar (orange-red).
What’s unusual about pararealgar is that it’s usually found on paintings as a result of aging. Realgar, a red arsenic sulfide pigment, turns into pararealgar over time. But because the yellow pararealgar in the gold elements of The Night Watch are mixed with orange semi-amorphous pararealgar, this wasn’t a logical explanation here. How would the orange have gotten in if the yellow was just caused by aging paint? The museum researchers could only see one explanation: Rembrandt did it on purpose.
To create the illusion of gold, Rembrandt heated yellow pigment (pararealgar) to create orange (semi-amorphous pararealgar) and mixed this with lead–tin yellow and vermilion to create something that looks close to gold.
Until this study, nobody knew that Rembrandt used pigments in this way. Even though the discovery came to light from chemical research, it was also backed up by historical sources that showed that arsenic sulfide pigments were relatively easy to acquire in Amsterdam at the time. One of Rembrandt’s contemporaries, painter Willem Kalf also used a similar mixture of pigments in his work.
This is just one small detail to come out of the much larger study of “The Night Watch” that has taken place at the Rijksmuseum in Amsterdam for the last few years. The museum has been keeping visitors up to date with news about the research on their website and in the gallery.
