For most of his life, Henri Rousseau was a tax collector. His nickname was “Le Douanier” (the customs officer). During his painting career, which began seriously in his middle years, Rousseau was characterized by critics as naïve and uneducated. After retiring, he supplemented his pension by playing violin, for which he’d won awards as a schoolboy, in the streets of Montparnasse. Rousseau is recognized as a self-taught master, and yet he’s little understood. “A Painter’s Secrets” is part of a wider technical study of the artist’s canvases, conducted by the Barnes Foundation, that focuses on the mechanics of his art. Between 2021 and 2024, five underlying paintings and eight reworked compositions have been discovered, and five paintings have been re-dated. Featuring 60 works—including The Snake Charmer and The Sleeping Gypsy—this show is the largest U.S. exhibition on Rousseau since 2006. —Jimmy Lux Fox