Curator's Choice: Duncan Thomson on swaggerless Gainsborough

THIS painting is one of Gainsborough's great full-length portraits but it has intriguing undertones. It's not your typical 'swagger' portrait, but a cross between a state portrait and a more profound work. It's a portrait of someone who's trying to present his best face to the world but isn't quite carrying it off. Rather than indicating his coronet, as would be customary, John Campbell, Fourth Duke of Argyll, seems to be grabbing at it for support. He seems to be looking towards an uncertain fate. His glance is that often used in an apotheosis, but here it seems uncertain. Unlike other swagger portraits, you want to get in close to it, to get up a step ladder and look at that face. It's an intimate portrait. The other wonderful thing about it for me is the concoction of crisp paint. The contrast of light is tremendous, particularly in the fragments of paint on the Duke's coat. Gainsbourgh didn't welcome being a portrait painter and took every opportunity to cut loose, which he does here in a wonderful incrustation of pigment.

Duncan Thomson is Keeper of the Scottish National Portrait Gallery, Edinburgh, where Gainsborough's portrait of 'John Campbell, 4th Duke of Argyll' is on permanent display

(Photograph omitted)