At different times during the 1950s and 1960s, Rothko produced a substantial quantity of small works on paper. It is not certain whether these are studies for larger paintings or simply smaller variations employing a similar dynamic of form and color. Rothko had many of them mounted on panel, canvas, or board in order to simulate the presence of unframed canvases. The smaller format especially suited Rothko in 1968, when his physical activity was dramatically curtailed by a heart ailment. Rothko continued to work predominantly on paper even after he returned to a relatively large format in 1969.