The 1840s saw Turner experimenting with square canvases. He shaped some, as here, into octagons. A pair to War, hanging nearby, it depicts the funeral of his friend, the artist David Wilkie. Wilkie died of typhoid in 1841 as he returned from the Middle East. Fearful the disease would spread, the Governor of Gibraltar refused to allow his body ashore and Wilkie was buried at sea. The island’s white cliffs are seen behind the ship. Turner imagines a funeral carriage on the ship’s deck, symbolising the public funeral Wilkie should have had. The painting was criticised for the blackness of its sails. Turner replied that he wished he could have made them blacker.

• Tate site