what is the medium of a sunday afternoon on the island of la grande jatte?
Artist: Georges-Pierre Seurat
Medium: Oil on canvas
Location: Art Institute of
Dimension: 81.7 in × 121.25 in
207.6 cm × 308 cm
The work exudes a feeling of harmony, not only in colors and form, but in the scene itself. While it is quite deliberately a mundane scene of a typical Paris afternoon, it carefully portrays all ages and social classes, coexisting peacefully.
Seurat’s first major pointillist work was Bathers at Asnieres (1883-4, National Gallery, London). Although rejected by the official Paris Salon, the work was shown at the Salon des Independants, an alternative event co-founded by Seurat himself, where he met fellow pointillists Paul Signac (1863-1935) and Henri-Edmond Cross (1856-1910), who helped him to further develop the idiom. Shortly afterwards Seurat began painting A Sunday Afternoon on the Island of La Grande Jatte, which took him two years to finish. It was exhibited for the first time in May 1886 at the final Impressionist exhibition: an ironic occurrence since the work is now seen as one of the first major examples of Post-Impressionist painting (1880-95).
Explanation of Other Modern French Paintings
In 1958, the painting was loaned out for the only time: to the Museum of Modern Art in New York. On 15 April 1958, a fire there, which killed one person on the second floor of the museum, forced the evacuation of the painting, which had been on a floor above the fire in the Whitney Museum, which adjoined MoMA at the time. 
The results of investigation into the discoloration of this painting have been ingeniously combined with further research into natural aging of paints to digitally rejuvenate the painting.  
So, the painting is about people gathering around outside on a nice, warm, and sunny Sunday afternoon in the park. There are lots of people in the picture. Some are sitting down and appear to be having a picnic. The river to the left is full of yachts and rowing boats. The river bank on the right has a slight incline and is populated by people of different ages. Perhaps the crowd is lazily witnessing a boat race? A relaxed ambience is presented.
In the summer of 1884, Seurat began work on A Sunday Afternoon on the Island of La Grande Jatte, which took him two years to complete.
It is the most famous example of use of highly systematic and “scientific” technique, subsequently called Pointillism. It relies on the ability of the eye and mind of the viewer to blend the color spots into a fuller range of tones. Seurat himself preferred to call his technique “chromo-luminarism,” a term he felt better stressed its focus on color and light.
Georges Seurat, Sunday at La Grand Jatte, 1884, Art Institute of Chicago, detail