Rachel de Ruvigny, Countess of Southampton

Van Dyck was the court painter of Charles the First and the inventor of the elegant, elongated style that dominated British portraiture for two hundred years. Look at the way the blue dress is painted, in long fluid strokes with highlights of pale silver, and at the transparency of the crystal ball, in which you can see reflections of the sky. The countess's face is composed and a little melancholy, her hair dressed in the loose ringlets of the 1630s. The clouds she sits on are painted thinly, so that the canvas shows through, while the dress is built up in thick, confident paint. The contrast between the earthly skull and the heavenly light is the whole meaning of the picture.

The portrait was bought through the Felton Bequest in 1922 and is one of the finest Van Dycks outside Europe. Several copies exist, including one at the Fitzwilliam Museum in Cambridge, and a cleaning in the late 1990s confirmed that the Melbourne canvas is the original. It matters because Van Dyck defined what a grand portrait could be, and this one shows him at the height of his powers, months before his own death. The memorable detail is the crystal sphere, which the young Turner admired so much that he sketched it when the painting was in England.

Did You Know? The young J. M. W. Turner was so struck by the crystal sphere in this portrait that he sketched it, and it influenced his own work.