Amidst his palette of reds and browns, Rembrandt used wheat, according to a new state-of-the-art analysis of two of his works.
It is the first study to identify wheat starch in any of Rembrandt's work, even though scientists have performed numerous analyses on more than 150 of the 17th-century Dutch artist's paintings. Rembrandt probably used wheat flour to make his paints stickier and more transparent, among other properties.
Identifying ingredients in old paintings can help curators decide how best to maintain, display and restore them. The study also offers surprisingly new insights into the techniques that Rembrandt dabbled with as he created his masterpieces.
"Scientific reports on Rembrandt's painting technique are so numerous that we did not expect to do much more than confirm what was already known," said Jana Sanyova, an analytical chemist at the Royal Institute for Cultural Heritage in Brussels. "The most striking result is undoubtedly the presence of starch, which to our knowledge has not been observed before in Rembrandt's work."
"He was probably looking for special effects," added Sanyova, who specializes in historical research on the materials and techniques used by ancient artists. "Rembrandt is known as a very ingenious and inventive artist-experimentalist who exceptionally mastered the use of his materials. The introduction of flour at the height of his career shows once more how he was keen for challenges."
For decades, artists and art conservationists have been interested in uncovering the secrets of Old Masters that lived centuries ago, particularly when it comes to lost or unrecorded information about what was in their paints.
In Rembrandt's time, artists mixed their own paints, which they then spread onto canvas in layers. Often, individual layers of the same piece of art contained different binding agents, pigments, varnishes and other ingredients. Besides color, each layer was mixed to just the right level of thickness, glossiness, texture, evenness on the surface, drying time and more.
But paint layers are tough to analyze because they are spread so incredibly thin. The thinnest ones rise just a thousandth of a millimeter above the layer below them.
Using a variety of chemical and physical analytical methods, along with old written records, scientists have been able to identify pigments and other inorganic materials in many ancient paintings.
But organic materials have been more difficult, mostly because the tiny molecules require high-resolution instruments to see them.
For the new study, Sanyova and colleagues used some of the most high-tech equipment around to look at the "Portrait of Nicolaes van Bambeeck," which Rembrandt van Rijn painted in 1641.
First the researchers took a cross-section from a miniscule section of the painting. Then they used a variety of methods to probe the layers, including a technique called Time of Fly -- Secondary Ion Mass spectrometry (ToF-SIMS). This technique involves sending a focused, high-energy beam of ions at the layered sample, then observing the ions that bounce back.
By analyzing the energy and chemical nature of the ejected ions, scientists can deduce detailed information about the types of elements and chemical bonds held within. For the second greyish layer of paint on the "Portrait of Nicolaes van Bambeeck," the scan showed, Rembrandt mixed oil and a small amount of lead with wheat flour.
Ancient painting manuals described the use of wheat starch or flour as a base layer of support on the canvas or paper. But the new study, published in the journal Analytical Chemistry, was the first to reveal the use of wheat before the 19th century as an agent for changing the working properties of paint.
It's not clear yet whether Rembrandt used wheat earlier or continued to use the ingredient after painting the "Portrait of Nicolaes van Bambeeck," who was a rich wool merchant.But Sanyova and colleagues also found wheat in the "Portrait of Agatha Bas," the merchant's wife. That supports a theory that Rembrandt painted the couple on the same piece of canvas and then cut the canvas in two.
Wheat flour probably helped Rembrandt make his oily paint thicker and more viscous, speculated Narayan Khandekar, a conservation scientist at the Harvard Art Museums in Cambridge, Mass.
Knowing what's in the layers of ancient paintings can help curators predict how the art will respond to temperature, humidity and other environmental conditions, he said. Wheat starch, for one, is very stable.
Beyond the practical applications, revealing the recipes of ancient artists can also provide an exciting new window into the past and an inspiration for artists of the future.
"It's rediscovering a lost technique," Khandekar said. "People are curious to know what Rembrandt used to paint with because he's one of the greatest painters. It's natural to want to know."