From Art Institute of Chicago online release:
This focused installation features pastels by four artists whose work was shown in the Impressionist exhibitions: Mary Cassatt, Edgar Degas, Eva Gonzalès, and Berthe Morisot. Their subjects range from scenes of modern life, such as ballet performers and a woman working in a hat shop, to depictions of intimate moments of bathing and women with children.
Although Impressionism is most closely associated with oil painting, during the late 19th century, Impressionist artists increasingly began to exhibit and market their prints and drawings as finished works of art. In fact, prints and drawings made up nearly half of the works in the eight Impressionist exhibitions held in Paris between 1874 and 1886. Pastels in particular became increasingly sought-after by collectors.
Pastel, a medium used to draw on paper or, less often, on canvas, is made by combining dry pigment with a sticky binder. Once artists have applied the pastel to the surface, they can either blend it, leave their markings visible, or layer different colors to create texture and tone. Pastel portraits had previously gained popularity in France and England in the 18th century, but fell out of fashion with critics when pastel was deemed too feminine; not only was it used by women artists, but it had a powdery consistency similar to women’s makeup. The Impressionists rejected this bias and instead embraced the medium’s ability to impart immediacy, boldness, and radiance.