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Walk into the Marsha Mateyka Gallery on R Street NW and you’ll be greeted by a series of smoothly minimalist rectangles, each in a single hue of blue, green, red, or yellow. The works’ plywood panels, with their shiny, subtly metallic pigments overlaid with thick layers of acrylic medium, are themselves assembled from smaller rectangles that have been fitted together like elements of a puzzle. The effect of the pieces is arresting—and a decided departure for Sam Gilliam, one of D.C.’s best-known artists.

Gilliam, 68, long worked with jagged, swooping lines and a multiplicity of colors in his paintings and painted sculptural installations. His work was raw and fluid, with colors bleeding into one another and thick overlays of conflicting and complementary patterns. Critic Walter Hopps once remarked on the “delicate balance between improvisation and structure and a sense of chaos controlled” in Gilliam’s works. The artist’s new exhibition, on view at Mateyka to May 18, shows no evidence of chaos at all. “It was time for a change,” Gilliam says.

“After moving into a new house and painting stripes on the wall, I was ready,” he explains of his foray into simple planes of color. “The prints came first.” Working on a computer, Gilliam in 2001 designed a series of templates for pieces such as that year’s Union Pacific and the series of diptychs and triptychs that followed. Working with Tandem Press in Madison, Wis., he collaged birch veneers onto paper and printed them with simple ovals and pure geometric shapes. “Before, I would always overprint, overstain,” says Gilliam. “This time [I chose] just to print a single time.” The paintings followed from this newly restrained approach.

Though Gilliam had previously worked with acrylic on plywood, in the late ’90s, he had moved his riotously colored pictures into three dimensions with a series of hinged parts that defied painting’s traditional flatness. Now, inspired by modernist Dutch designer and architect Gerrit Rietveld—who was influenced by painter Piet Mondrian and made furniture reduced to planes of wood painted in primary colors—Gilliam has returned to the flatness that he so long avoided. And he’s christened his new works “Slats,” in homage to the shapes from which some of Rietveld’s chairs were built.

“Unless you have this kind of freedom in the material or the way you make art,” Gilliam says, “by some standards, you may not be an artist.” —Garance Franke-Ruta