Joseph Yoakum, who died in 1972, said he routinely started drawing without knowing what the end result would be. His 1969 piece above, which is included in the exhibit, turned out to be of a national park in Utah. “It’s a celebration of the wonders of nature,” NGA curator Lynne Cooke says. “Some of the dark shaded areas, they help give mass and volume to the mountain. … They suggest the movement of clouds and sun. It’s a very alive landscape.”

Nutt’s 1970 piece “Toot-Toot Woo-Woo,” is vivid, graphic and cartoonish, as well as exactingly crafted. The reverse-glass technique he used — painting on the back side of a piece of clear Plexiglas — required that he plan every single detail before applying a single drop, since the process doesn’t allow for painting over mistakes. (Courtesy Elmhurst College Art Collection)

The bulk of the art on display at the National Gallery of Art, like that of most national galleries, was made by mainstream artists — often well-heeled white guys who went to art school or apprenticed with other well-known painters. This week, the gallery opened an exhibit of works created by unschooled artists — a group more likely to include women, poor folks and African-Americans.

For curator Lynne Cooke, “Outliers and American Vanguard Art” is even more notable for being the rare outsider-art exhibit to also feature pieces by the mainstream artists who championed their colleagues on the fringes.

“Over the last century, the major advocates of self-taught artists have been professional artists,” Cooke says. “They often found the self-taught artists to be inspirational models of independence and a creative drive indifferent to the fortunes of the market or to current tastes.”

Jim Nutt, one of the most celebrated living American artists, helped shine a spotlight on the work of Joseph Yoakum, a self-taught artist of African-American and American Indian descent. Born in 1890, Yoakum didn’t begin drawing until late in life, Cooke says. His early years were full of travel and adventure: He grew up in Missouri, and then ran away and joined the circus in his early teens. He worked as a coal miner in Kansas before being drafted into the Army at the beginning of America’s involvement in World War I. He traveled after the war and eventually settled in Chicago, where he began drawing decades later, spurred on by a dream he had in 1962.

Joseph Yoakum (Courtesy Prints and Drawings Dept., Art Institute of Chicago)

In 1967, “he hung some of his drawings in the window of his storefront apartment, and someone teaching at Chicago State College saw them and got very excited,” Cooke says. That led to small, local exhibitions where “influential artists like Jim Nutt saw them, and felt really vindicated in their own bid for independence and fantasy and the need to follow their own imagination.”

Nutt and other insider artists pushed for increasingly prestigious exhibits for Yoakum’s drawings, which brought his work into the mainstream.

The “Outliers” exhibit focuses on three time periods when the mainstream was particularly open to self-taught artists like Yoakum. The first, from 1924 to 1943, was driven by the Great Depression and the government funding of artists through the Work Projects Administration. The second period, 1968 to 1992, was brought on by the civil rights movement and pushes for equality by women and gays. The third, from 1998 to 2013, was driven by globalization that resulted in a collapse of distinctions, whereby insider and outsider artists could be shown side by side, Cooke says.

Jim Nutt (Courtesy Jim Newberry)

Where are we now? It’s hard to say, but artists seem to be setting the tone, Cooke says: “Museums of all kinds — whether historical collections like this one, or modern and contemporary art museums — are thinking about diversity and inclusion and exploring it in a number of ways, and this [exhibit] is spearheading that exploration.”

National Gallery of Art, East Building, Fourth Street and Constitution Avenue NW; through May 13, free.