It’s a small work of art — precisely the size of an old Savarin coffee can jammed with artist’s paintbrushes — but in the history of postwar art and in the career of Jasper Johns, one of the most important artists of the last half century, it looms large.

Created in 1960, “Painted Bronze” has been a fixture for more than three decades at the Philadelphia Museum of Art, where it has been on long-term loan from Mr. Johns’s personal collection. But now it will migrate north to a permanent home at the Museum of Modern Art, which will receive the sculpture as a promised gift from the collectors Henry R. Kravis and his wife, Marie-Josée Kravis, the Museum of Modern Art’s president, who recently bought it.