BEACON, N.Y.—Even the sunlight that streams through the glass walls of Dia:Beacon on an early summer afternoon cannot break through the mysterious darkness cast by the paintings of Antoni Tàpies. Although they are diverse in color and texture—some are cultivated from an earthy palette while others are as cool and smooth as a slab of slate—all 20 of the works on view at “Antoni Tàpies: The Resources of Rhetoric,” at the outpost’s Riggio Galleries here until October 19, seem to be inconsolably morose. Like the rest of Tàpies’s paintings, which have not been surveyed by a major U.S. institution in decades, they are full of secrets as big and deep as their monstrously sized, densely layered surfaces.

Several years ago, I paid a visit to Tàpies at his home in the ritzy Barcelona neighborhood of Gracia. As we drank tea and spoke in a fumbling mixture of Castilian and Catalan, I stole glances at the Mirós and Picassos that flickered throughout the dimly lit apartment and awkwardly tried to edge the conversation toward the subject I’d come to discuss. I had read his memoir and his many essays on art, but I was still perplexed by the sphinxlike quality of his paintings. Above all, I could not get over the fact that his best work—including most of the canvases hung in the Dia show—comes from the 1950s, ’60s, and ’70s, decades that coincided with the reign of Spanish dictator Francisco Franco. I wanted to know how Tàpies had managed to execute work so modern and, at times, subversive under such a notoriously repressive regime. But when I asked the octogenarian painter what it was like to live in Spain during the Franco years, he just smiled and said, “That was a long time ago.”

His brush-off seemed like a perfect example of el pacto del olvido, or the pact of forgetting, a widespread phenomenon that was the inspiration for Giles Tremlett’s best-selling The Ghosts of Spain. Like many of his compatriots who were pleased with how quickly the country had moved toward a stable democracy following Franco’s death in 1975, Tàpies did not wish to discuss the past. But as an artist whose success defied the odds in a period marked by brutality and intolerance, he was not going to get off the hook that easily. In the end, he budged, giving me a glimpse into an era that, for many of us, is still somewhat of a mystery.

The most well-known story of an artist in the Franco era ends with the assassination and anonymous burial of the Andalusian poet Federico García Lorca. That dark tale has been the focus of no less than two New Yorker articles in recent years, and it is only a matter of time before the incident makes it to the big screen. Yet Tàpies’s story paints a very different picture of what happened to artists living under Franco. Despite being an artist whose ideological résumé (atheist, communist, supporter of Catalan autonomy) defied three of the regime’s defining characteristics (Catholic, anti-socialist, nationalist), somehow, in the second half of the 20th century, Tàpies became the reigning cultural king of post-Picasso Spain.

In 1936, when the Civil War erupted, Tàpies was about to turn 13. During that period, the Spanish art world had more than its fair share of Alfred Rosenbergs—conservative critics who cannibalized the very vanguard movements that their fellow Spaniards had conceived in the first quarter of the 20th century. But even the most ardent enemies of Cubism ceased their polemics when they realized that artists mimicking Velásquez and Goya wouldn’t exactly usher in a new Golden Age; the irreversible advents of photography and Impressionism had forever altered the landscape of 20th-century painting, and it was too late to go back to the good old days. By the time Tàpies participated in his first public exhibition in 1948, the pendulum had swung away from nostalgic revivalism and once more toward the avant-garde.

But the truce with modern art was tentative and certainly did not guarantee the right to free expression. In our interview, Tàpies remembered that during his first solo show in 1950, the dealer Josep Gudiol became frantic when a gallery patron complained of the sacrilegious nature of one his etchings, which depicted a grotesque priest. Without a second thought, Gudiol tore it from the gallery wall.