This pen-and-ink wash drawing is an elaborate design for the painted decoration of a staircase. Grand mythological scenes cover the walls, framed by imposing illusionist architecture. The Birth of Venus appears at ground level. Surrounded by attendants, her swans below, Venus is seen rising from the foam of the sea which, according to the Greek poet Hesiod, was produced as the result of Cronus castrating Uranus with a scythe. Cronus was later identified as the Roman god Saturn, who appears directly behind Venus, his scythe borne aloft. The scene is surveyed by the gods on Olympus, who appear on the ceiling sprawling on clouds, presided over by Jupiter who is flanked by his wife Juno and his attribute the eagle, the sun radiating behind him. Mercury, the messenger of the gods, hovers between the earthly and godly spheres while, on the wall rising up the stairs, the sea god Neptune appears in his chariot.
The scheme, minus Neptune, is almost identical to an oil sketch by Thornhill at the Victoria and Albert Museum, and presumably is a preliminary design for it. It was Thornhill's method when devising an interior to begin with rapid pen or pencil drawings, selecting and rejecting subject matter and compositions as he went. As the design progressed, the drawings become more detailed and worked, resulting finally in an oil sketch. It has been suggested that the oil sketch at the Victoria and Albert Museum, along with two others which are perhaps alternative designs for the same space, are connected to Thornhill's work for James Brydges, 1st Duke of Chandos at his celebrated mansion, Canons, in Middlesex. Constructed between 1713 and 1725 the house was magnificently decorated but, owing to Chandos's princely living outstripping his means, was pulled down in 1748. Thornhill painted the Saloon and some contemporary sources say the staircase as well, although others give this to Francesco Sleter (1685-1775), which on balance is probably correct. The dimensions of this sketch do not fit the narrow, rectangular space known to have been occupied by the staircase from floor plans of the house; most likely the scheme is for another, unidentified, location.
British Watercolours from the Oppé Collection, exhibition catalogue, Tate Gallery, 1997, no.3 p.42
Jacob Simon, English Baroque Sketches, exhibition catalogue, Greater London Council, Marble Hill House, Twickenham 1974, unpaginated, between nos.44-47