The sketches, chosen to represent the many stages in his prolific career, reveal a fascination with landscapes. Landscapes offer every variation on a theme with paths, woods, distant views, animals and even the occasional human.

The finely pencilled Pathway through a Wooded Landscape with a Farm in the Distance (1747), gives a sharp sense of distance, while Wooded Landscape with Cottage, Peasant, Cows and Sheep (1777-8), suggests rather than realises the details of the background. The latter shows Gainsborough's technical inventiveness - he used black chalk, white lead, ochre, red and green washes on the paper, and for final effect, even dipped it into a mix of skimmed milk and varnish. Some landscapes have a definite Suffolk feel, but locations are not identifiable.

Gainsborough didn't restrict his drawing to landscapes. In Study for Diana and Acteon (1784) he presents the story of the virgin goddess of hunting who turned Prince Acteon into a stag and destroyed him with his own hounds for the mistake of seeing her bathe naked. The supple, bending figures have a translucent quality and are more human than mythical.

Gainsborough is best known for his portraits of rich customers wanting their lives, and sometimes properties, preserved for posterity. The charming little sketch of Anne Lynch, done when he was only 17, shows the emerging skills for which he later became so famous. Her tiny waist and direct gaze gave him plenty to work on. Study for the Portrait of Ann Ford (1760) on a luxurious blue paper, tantalizingly outlines her frilly dress. Peasants Going to Market (1770-74) is a powerful group study, with a dog showing the way to two donkeys and their human loads. Their detailed figures richly dominate the foreground.

Joshua Reynolds described the skills of his contemporary Gainsborough, by which he was intrigued, as "all those odd little scratches and marks". To see the scratches and marks, and be intrigued yourself, visit the exhibition which runs until March 24.