When fire tore through the Museum of Modern Art in 1958, staff rushed a colossal canvas out through the adjoining Whitney to save it. Yet the greatest threat to Georges Seurat's A Sunday Afternoon on the Island of La Grande Jatte was already inside the paint. This episode explores the secretive, disciplined artist who spent two years from 1884 to 1886 covering a roughly 7-by-10-foot canvas in tiny dots, and the chemistry that began turning his brightest yellows brown while he was still alive.

We explain Michel-Eugène Chevreul's law of simultaneous contrast, how divisionism turns the viewer's retina into the mixing palette like a digital screen, the three stages of the painting including its dotted border, the instability of zinc yellow, the bourgeois figures frozen in shadow versus the sunlit workers of Bathers at Asnières, the woman fishin ...