This painting was once described as the most beautiful of all the artworks of the 19th century. Certainly it seems the happiest. But beneath renoir's joyful portrayal of working class Parisians at leisure is another, darker story.

Perhaps the most reproduced of all 19th century paintings, The Sunflowers has a story that lies at the crux of the complex relationship between Van Gogh and Paul Gaugin. The programme reveals how Van Gogh started to paint sunflowers soon after he moved from Holland to Paris and how they became the emblem of his embrace of Southern France, warmth and the sun. It looks especially at the 8th of the Sunflower paintings, the one in the National Gallery in London which is arguably the best in the series. It was most admired and desired by Gaugin but denied to him by Van Gogh as their relationship deteriorated.

A popular masterpiece and yet an enduring enigma. It seems to show a quiet scene in a Paris park but there are hints at the demi-monde, if you know where to look. The most remarkable aspect of this vast canvas however remains Seurat's technique his revolutionary pointillism.