Robert Indiana kept a series of illustrated journals during the late 1950s and 1960s, in which he discusses the development of his work as well as his daily life on Coenties Slip.

Indiana's journal page for February 21, 1961, includes a sketch of the painting Eidolons (destroyed), with a note that he stenciled several "Eidolons." He also records that he added the text "The Sweet Mystery" to the painting of that name, and that John photographed him doing so (likely a reference to the photographer John Ardoin). 

Indiana also notes buying the magazine Holiday, which had a "handsome [Hans] Namuth photograph of Jack [Youngerman] in article on succeeding in New York."