Jennifer Montagu kindly confirmed the attribution to Algardi. The Ferretti drawing is similar in handling to one for the Arms of Camillo Pamphili at Holkham Hall, J. Montagu, Alessandro Algardi, New Haven and London, 1985, II, no. 47, I, fig. 109. Three other designs for frames by Algardi are illustrated in Montagu, op. cit., I, figs. 222 and 233, II, nos. 80-3, pl. 185.