On an agitated sea, we can make out people, boats and sails. The shifting colours and lights bring out the haze, the winter sun through the clouds and the powerful swell of the waves. This is one of a series of atmospheric coastal scenes Turner painted in the 1840s. Despite his position as one of the leading figures of British art, this work has rarely been shown. But it is an extraordinary example of Turner’s technique, which already in his lifetime was aptly described as ‘airy visions painted with tinted steam’.