Applying science
The scientific discoveries and inventions of the 19th century had an important influence on the way painters worked. New research encouraged artists to experiment with complementary colours.
For instance, in Renoir's The Skiff (La Yole), he places an orange boat against cobalt blue water. Orange and blue were understood to be opposite one another in the colour spectrum, and by placing them next to each other, each looked deeper and brighter.
Even more significant to the Impressionists was an interest in the way in which the human mind processes what it sees. When we look at a landscape, or a crowd of people, we do not instantly see every face, or leaf in detailed focus, but as a mass of colour and light. Impressionist painters tried to express this experience.