Guercino’s picture was painted around 1619 for Cardinal Jacopo Serra. Turner set out what is probably a colour key of this picture on folio 52 verso of this sketchbook, facing his copy, and further comments on folios 54 recto and verso (D04341, D04343, D04344). Here, and in a later Perspective lecture at the Royal Academy when he praised its ‘sepulchral darkness’, he believed the picture to be by Domenichino.1 Turner also thought Guercino’s Mars and Venus to be by Domenichino; see folio 36 (D04320) and his copy on folio 35 (D04319). See also folio 37 (D04322) for a copy of a Guercino Virgin and Child then in the Louvre.
For the lecture text, see John Gage, Colour in Turner: Poetry and Truth, London 1969, p.208.