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.

This journal page covers February 14–15, 1961. Indiana's first entry, for February 14, 1961, includes a sketch of Eidolons, a painting on Homasote (later destroyed), with the notes "add coat of Mars black" and "raw sienna." "Poe" appears in parentheses below the work's title, possibly a reference to Edgar Allen Poe's poem "Dream-Land," whose third and fourth lines read "Where an Eidolon, named NIGHT,  / On a black throne reigns upright." 

The entry for February 15, 1961, consists of a sketch of The Sweet Mystery, with note "add stripes [to] Sweet Mystery."