Art and Physics Converge: Accidental Painting

When artist David Alfaro Siqueiros first discovered his “accidental painting” technique in the 1930s, the simplicity of the process coupled with its elaborate results riveted him. Siqueiros simply poured different color paints onto a wooden panel, allowing the different colors to spread, coalesce, and infiltrate one another.

“When he discovered this process, he wrote a very long letter to his girlfriend,” said Sandra Zetina, an art historian at the National Autonomous University of Mexico. “He wrote very beautifully about this.”

Siqueiros fell in love with the aesthetics, but the underlying science sustained his enthusiasm; he even invited scientists to his workshop to explain the physics behind his painting techniques. The scientists, however, had trouble understanding what Siqueiros wanted from them, according to Zetina.

Fast forward to the 21st century. Zetina, like Siqueiros, wanted to understand how these beautiful paintings formed. She needed an expert in fluid dynamics, and she eventually found just the right physicist at her same university — Roberto Zenit. Together, they’ve unraveled this scientific art form.

Zenit and Zetina's beautiful video detailing their research.
Best viewed directly on YouTube.

The Physics of Art

To reproduce Siqueiros’ technique, Zenit and Zetina acquired paints similar to the ones Siqueiros had and a flat, horizontal surface. For the experiment, the pair poured one color of paint onto the surface, allowed it to spread, and then poured another controlled amount of a different color.

The researchers strayed from Siqueiros’ technique in one key area, however. The flat surface was transparent, allowing the researchers to film the paints’ interactions in high definition.

HD film revealed what Zenit had suspected: The mixing and “infiltration” of colors resulted from an imbalance between the paints’ densities.

When a denser fluid rest atop a less dense one, the top fluid wants to move downward, causing the two fluids to mix. Different colors of paint have different densities because of the varying compounds used to make pigments.

Black paint, for instance, tends to be less dense than white paint. Consequently, Zenit and Zetina found that pouring white paint onto black paint would lead to the desired mixing. Black on white, however, would not.

In physics, this battle between densities is called a Rayleigh-Taylor instability, and it crops up in a number of areas outside of art. In astrophysics, for instance, exploding stars expel gases of varying densities, leading to the formation of Rayleigh-Taylor “fingers.”

Rayleigh-Taylor fingers can be seen in the Crab Nebula.
Image Credit: NASA/ESA

Engineers also rely on this instability when digging for oil. Injecting air to unlock oil, for instance, is a very inefficient process because of this instability, but fracking fluids lead to more efficient extraction. Anytime two fluids with different densities interact, you can find this instability.

Although the instability causes the paints to mix together, other physical processes help determine what the painting will look like. Viscosity — or the “thickness” — of a fluid partly determines how far the paints will spread before drying. Consequently, Zenit and Zetina created different types of paintings with paints that varied in not only density but also viscosity.

According to Zenit, Siqueiros seemed to have a feel for these physical dynamics.

“He was a true intellectual,” said Zenit. “He really had an empirical understanding of how liquids flow in paintings.”

A Marriage of Ideas

Siqueiros’ interest in physics extended beyond his techniques and into the actual content of his paintings as well. In the 1940’s, atomic bombs influenced much of Siqueiros’ work, and he developed a keen interest in the patterns found in explosions.

One such painting initially sparked Zetina’s interest in the science behind Siqueiros’ patterns, prompting her to seek Zenit. Since their collaboration, both the physicist and the art historian have developed a deeper appreciation of each other’s fields.

Many artists, for example, understand what methods cause paint or lacquer to flow in different ways – an understanding developed through trial and error. Although Zenit enjoys understanding the underlying science, science can never fully explain the aesthetic complexities of artwork, he said. For that, he defers to the artists.

Zenit and Zetina hope to build upon the research displayed in their video, eventually publishing in an academic journal. Further still, both researchers have expressed interest in teaching students from each other’s disciplines on this collaborative research.

Siqueiros inspired this interdisciplinary research, and both Zenit and Zetina believe that he’d approve of their investigation. Despite Siqueiros’ chosen profession, Zenit thinks he would have excelled in a variety of areas.

“He had intuition about the physical processes,” Zenit said. “He would have been a good physicist.”