Impressionism is defined by a reaction to the growth of photography in the 1830s onwards. Painters were in a panic and began to redefine what art should be as photography came to dominate realism and traditional portraits. Artist began to try to capture the light outdoors at a certain time around sunrise or sunset called Golden Hour. The brushwork was much looser in a reaction to photography. One version called pointilism developed as dots on the canvas vs. short stroke of Impressionism. The painters would place contrasting colors next to one another on the canvas to make them pop and vibrate. So to make a "green" a painter may put a yellow next to blue in small strokes, which became green. An "orange" may be made by placing red next to yellow. Another trait adopted was that many artists in this style refused to use black in their painting leaving a lighter mood in the painting. As you can see in Van Gogh's painting you see the contrasting colors laid next to one another for this pop effect. The style originally ran from 1880s to 1900, but many artists still use this in their painting. You can see in some of my painting especially seascapes how I use this technique in the water.