Nocturne in Blue and Silver: The Lagoon, Venice

In about 15 months in Venice, Whistler made more than 50 etchings and some 90 pastels, and only three oil paintings, by the museum's count. This is one of them. He stood near the Piazzetta, by the Royal Gardens, and looked south-east across the water at night. The tower and church of San Giorgio Maggiore rise on the right as a dim silhouette, a few gondolas float half-seen, and the lights of the Lido make a thin line along the horizon.

The shimmer has a practical cause. A conservator examining the canvas in Boston in 2007 found a ground and the start of another painting on the back. Whistler seems to have turned the canvas over and worked on the rough, unprimed side, laying thin blue-grey layers that sink into the weave and leave the tips of the threads catching the lower colour. Then he rubbed the paint down so that the boats and the church blur into the dark.

The picture was never shown in his lifetime. His sister-in-law later said that Carmen Rossi, a model who sat for him for many years, had taken it out of his Paris studio. Nothing was proven, and Whistler, who was fond of her, never acted against her. It came up at auction in Paris in November 1903, four months after his death, as the first lot of the sale.