Fiesta musical, castillo de East Cowes

For most of a century this canvas was catalogued as a scene at Petworth, the Sussex house where Turner kept a studio in the 1830s. The room turned out to be somewhere else. The art historian Patrick Youngblood matched its curved corners and deep bay window to the octagon room at East Cowes Castle on the Isle of Wight, the house the architect John Nash built for himself.

Turner stayed there in 1827 to paint the regatta and was back on the island in the early 1830s, nearer the date of this picture. Nash's wife was a serious pianist, which is roughly what you are looking at, figures gathered around music indoors.

He never finished it. It came to the nation in 1856 with the rest of his studio, some 300 oils he had kept back.