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The attribution to Guercino of this newly-discovered, double-sided drawing is confirmed by the study on the verso of a kneeling man with his hands tied behind his back, which is an early idea, probably drawn from life, for St James's companion in Guercino's lost altarpiece of the Martyrdom of St James the Greater, painted in 1627 for the Cappella Prini in SS. Pietro e Prospero, Reggio Emilia (Salerno, I dipinti del Guercino, 1988, p. 209, no. 118). The artist began the altarpiece while still at work on his frescoes in the cupola of Piacenza cathedral.
The appearance of this lost altarpiece survives, in reverse, in an engraving (above)

Giovanni Francesco Barbieri, called GUERCINO (Cento 1591 - 1666 Bologna)
Leaning Nude Man (recto); Kneeling Man, Hands Tied Behind His Back (verso)
Black chalk heightened with white on light blue-grey paper
18 1/8 x 13 3/4 in
46 x 35 cm
46 x 35 cm