Jean Goldman has kindly pointed out that this drawing is an early study for the Prophet Zachariah for the cupola of the Cathedral at Piacenza. Guercino received the commission to decorate the cupola in 1626 following the death of Morazzone, who had begun the cycle the year before. The space was divided into eight compartments, each to be filled with a prophet over a putto holding a flag. Morazzone had already painted two compartments when Guercino took over. Between May 1626 and November 1627 Guercino finished the commission, and painted four scenes of the Life of Christ and eight sibyls flanking the windows. He prepared for the cupola with numerous drawings, listed by P. Bagni, Gli affreschi del Guercino nel Duomo di Piacenza, Padua, 1994, nos. 17-35.
This drawing, along with one in the Mahon Collection, one at Windsor Castle and another in a private collection in Chicago, are all related to the Prophet Zachariah. Each of these four preliminary drawings show minor changes made by Guercino before he arrived at his final composition. In the present drawing Guercino introduced the book held by the prophet, and shifted the supporting position on the other arm. He also drew the figures with the legs crossed rather than splayed. The drawing is very close in handling, technique and size to the previous one in the series, now at Windsor Castle (D. Mahon and N. Turner, The Drawings of Guercino in the Collection of Her Majesty the Queen at Windsor Castle, Cambridge, 1989, no. 38, fig. 39).
Sir Denis Mahon has kindly confirmed the attribution to Guercino, dating the drawing to the time of the Piacenza commission. We are grateful to Jean Goldman for providing the information contained in this note.