At the end of 1917 Matisse settled in Nice, where he spent most of each year for the remainder of his long life. In the decades that followed he did not forget his period of extreme experimentation. Around 1931 Matisse returned to Back. The final state, made from a cast of Back (III), is a starkly refined, highly architectural monolith in which the struggles of the earlier states have been smoothed away. Matisse kept a plaster version of Back (IV) in his studio for the rest of his life, and it is visible in photographs with his late, monumental paper cutouts (below), which—like his works of 1913–17—combine pictorial and sculptural characteristics. All four Backs were unique plaster bas-reliefs until 1950, when Back (I), (III), and (IV) were cast in bronze; Back (II) was not discovered until 1955, a year after the artist’s death, and it was cast a year later.
from Matisse: Radical Invention, 1913-1917, July 18–October 11, 2010