Young Woman Powdering Herself
In this particular painting, Young Woman Powdering Herself, the modulation of light and shadow on the wall is achieved with the use of small dots of pure colour juxtaposed in varying concentrations and intensity. The young model depicted by Seurat was his mistress, Madeleine Knobloch, who bore him two sons, and this painting therefore takes on a very personal meaning.
A hidden self-portrait
An even more personal touch was revealed by a scanner created by the Italian Institute of Optics, showing that the vase of flowers in the top left-hand corner of the image was originally a reflection of Seurat at work, and would have been the only self-portrait of the artist to exist.
See this painting in The Courtauld Gallery