Cy Twombly was a postwar art-world giant, as is Jeff Koons. Other than that, the two artists have little in common. Koons’s machine-made fabrications are reductive and bold, and take inspiration from mass media. Twombly was a proponent of gestural mark-making freely scribbled, a technique he called “romantic symbolism.” While Koons’s work is in-your-face accessible, Twombly’s was once described by the curator Kirk Varnedoe as “truculently difficult not just for a broad public, but for the sophisticated inmates of postwar art as well.” The Bastian exhibition places works by Koons—his “Gazing Ball” series as well as the painting Primal Swish—in conversation with Twombly’s Untitled, a set of six lithographs. The juxtaposition teases out hidden similarities between the two artists. —E.C.