Postwar painters took nothing for granted, not even the shape of the canvas. From Frank Stella to Elizabeth Murray, the pioneers of shaped painting abandoned the familiar rectangle to explore alternative geometries. Shaped canvas represents its own branch of painting’s evolutionary tree. Along the way, some creators edged out others. Ellsworth Kelly is a household name. Charles Hinman got left behind. 

Now on view at the Kreeger Museum, Charles Hinman: Structures, 1965–2014 is an effort to remind viewers of the pioneering role he has played in exploring the sculpture of painting. As one of the first artists to bend two-dimensional paintings into three-dimensional formats, Hinman opened up new ways of thinking about the genre. Structures shows how Hinman unlocked painting, but the show also hints at why he isn’t better known today.

“Sails” (1965) is emblematic of Hinman’s work. The painting is a configuration of irregular tiles arranged in a flaglike shape. At a point where several of these monochrome sections meet, the painting bulges, as if it were being pressed outward from behind. The verso side of “Sails,” a painting originally purchased by David and Carmen Kreeger, reveals a patchwork construction of intersecting stretcher bars (wooden beams that artists use to support canvas in a painting).

That was Hinman’s innovation: His paintings jut into three-dimensional space, as if they were wall-mounted sculptures. Hinman’s paintings have a physicality to them; “Sails” looks like a fat gumdrop. Alongside the many paintings on view, curator Danielle O’Steen provides preparatory drawings and diagrams to show the meticulous construction behind works such as “Canary Islands” (1988). While the paintings themselves tell little about how they were made, the schematics, along with documentary video from the artist’s studio, reveal a sculptor at work.

Hinman shares a lot of affinities with Ellsworth Kelly, especially in his early works. Hinman’s brushstroke looks automatic, as if his acrylics were applied industrially, just as in Kelly’s work. Hinman favors the same bold primary and secondary colors as Kelly. While Kelly favored simple geometric shapes like rhombuses and sectors to carry his palette, Hinman’s shapes, at least in his early paintings, are more abstract. The most satisfying paintings in Hinman’s show—“Cloud,” “Red Wing,” and “Interlocking,” a trio of 1965 paintings that belong to the Hirshhorn Museum and Sculpture Garden—are graceful abstractions full of potential. These three paintings showcase alert new ideas in Pop Art and Minimalism, with Hinman’s contribution being the foray into three-dimensional space.  

With the support of prominent modernist collectors such as the Kreegers and Joseph Hirshhorn, Hinman was hardly unknown in his day. The critic Lucy Lippard observed at the time how Hinman’s topological paintings conveyed speed, as O’Steen notes. Hinman was excluded from the definitive 1964 show at the Solomon R. Guggenheim Museum, The Shaped Canvas, but so were other painters who were pushing the three-dimensional boundary. And the next year, Hinman’s work appeared in Shape and Structure, an important corrective at the Tibor de Nagy Gallery, a proving ground for postwar painters. 

Hinman was in the right place to make good on his innovations in the New York art scene. But he retreated to safer ground in the 1970s, jettisoning the color from his paintings, for example, to focus on shape. “Happy Landing” (1974) and “White Rise” (1976) look like jumbles of white quartz crystals. Soft pastels make an appearance in his work in the 1980s. “Watkins Glen” (1987) is a hard-edged geometric painting, like most of Hinman’s work, but it’s a gentle retread of his earlier themes.  

Later experiments in material have paid off for Hinman, including “Perseids” (1999) and “Andromedids” (2003), both paintings on wood and Lutradur, a spun textile that’s a cross between paper and fabric. “Trieste” (1982) and “Vulcan” (1983) are both works Hinman made by casting paper in a mold, a technique usually reserved for making bas-relief impressions. These abstractions are even more impressive than Hinman’s exquisite maquettes, which clearly play to his strengths as a sculptor.

Recent works from Hinman’s “Gems” series, such as “Onyx” or “Indochinite” (both 2013), betray his fascination with space. Hidden from view, brightly colored panels on the underside of these paintings make the wall behind the paintings appear to glow. The new works find Hinman still determined to chart a course through shaped canvas, even though it has led to diminishing returns as his works have grown less evocative and more representational. 

Earlier this year, viewers in D.C. got another look at a master of shaped paintings: The Phillips Collection held a retrospective of the Cuban-born, Puerto Rico-based painter Zilia Sánchez. It’s hard not to compare the two exhibitions (and indeed, the curators spoke together in a two-part conversation held at each museum in May). The Phillips Collection show made the case that Sánchez, a sensual abstract painter, deserves greater recognition for using shaped canvas to push boundaries in both Minimalism and Surrealism.

Structures at the Kreeger Museum makes a different case: Hinman may have missed his true calling as an architect. At times, Hinman’s paintings are not as compelling as the means he used to produce them. Maybe the best works in the show are the precise graphite and charcoal studies he generated for paintings such as “Cohesive Three” (1974). The care and exactitude Hinman shows in preparing paintings that work in space suggest that maybe he should have been building all along. 

At the Kreeger Museum to July 31. 2401 Foxhall Road NW. $8–$10. kreegermuseum.org.