At the San Francisco Museum of Modern Art hangs a gilded frame containing what looks like a blank, faintly smudged sheet of paper. It is Robert Rauschenberg's Erased de Kooning Drawing from 1953, and this episode explains why a museum would acquire and protect an absence. It starts with Rauschenberg's White Paintings, his frustration that erasing his own drawings looked like discarded drafts, and his realization that a meaningful erasure required destroying real artistic capital.

From the Cedar Tavern to Jasper Johns's frame and label, the hosts unpack how a month of scrubbing became one of the most provocative acts in modern art, and how infrared imaging decades later revealed the ghost underneath.

• How Rauschenberg approached Willem de Kooning with the request, expected a refusal, and instead received a dense charcoal and pencil ...