"Pat Lyon at the Forge" by John B. Neagle, oil on canvas, 1829. Pennsylvania Academy of the Fine Arts, Philadelphia; on view at the National Portrait Gallery's "The Sweat of Their Face: Portraying American Workers" exhibit. (Pennsylvania Academy of the Fine Arts/Pennsylvania Academy of the Fine Arts)

Once upon a time, there was a promise that man's dominion over the world would lead to shared prosperity and leisure. As we made machines to do our bidding, we would gain time to tend to our families and communities and pursue the improvement of our minds and spirit.

That promise never came to pass, and today the mechanization of labor is increasing more rapidly than ever, dragging legions of once middle- and working-class people into unemployment and despair. The great promise of technical mastery of the world has led to increasing inequality, and for many, penury and new forms of peonage.

And so we have exhibitions like "The Sweat of Their Face" at the National Portrait Gallery, which looks at how workers have been represented in this country since the early days of the republic. At one end of the spectrum is a dramatic 1829 painting by John Neagle called "Pat Lyon at the Forge." It depicts a ruddy, healthy, well-knit middle-aged man standing at a glowing forge with a hammer in his hand, staring straight at the viewer with a look of steely, democratic self-confidence. At the other end is a Lewis Hine photograph from around 1910, showing small girls at labor on the bare dirt floor of a tobacco barn, stringing leaves together at a crude table that is almost as tall as they are.

Pat Lyon was a moderately wealthy artisan and entrepreneur who embraced his identity as a worker over any pretensions to upper-class refinement. The young girls in Hine's photograph are anonymous toilers, exploited and miserable. The success of America, as an ideology, is that when we think of work, we tend to think of the dignity of Pat Lyon, not the hundreds of millions for whom work is degrading, dehumanizing and destructive.

The exhibition, organized by curators David C. Ward and Dorothy Moss, is more than a history of labor through pictures. It grapples with the difficulty of defining what is a portrait, and with the fact that workers were not often the subject of portraits, especially in the days before photography. And even with the advent of the camera, photographers weren't necessarily using the lens to capture workers with the same dignity, intimacy and personality that one finds in photographs of the bourgeoisie. Rather, photographers and especially photojournalists sought out types, ethnographic evidence and social data. The "worker" didn't exist within the formal understanding of portraiture throughout much of American history.

"We Can Do It!" by J. Howard Miller, photolithograph, c. 1942. (Smithsonian National Museum of American History/Smithsonian National Museum of American History)

Images of workers abound in paintings, but they aren't always portraits, and they don't necessarily give us much insight into personality or character. Consider the women gathered in a field in the early light of day in Winslow Homer's "Old Mill (The Morning Bell)." Are they merely decorative? Is the buxom, smiling figure in Lilly Martin Spencer's 1851 "The Jolly Washerwoman" a real person or a caricature inserted to enliven a picture dominated by the tools of her trade, the washboard, soapy wooden bucket and metal pails of wet clothes?

The story of labor in America is mainly one of misery, from the turmoil of industrialization to the vicissitudes of the market economy with its periodic and horrendous crashes and the alignment of state power with the corporate class. The foul synergy of racism, sexism and classism continues still. Propagandists would occasionally attempt to imbue the worker with dignity, and from time to time, America would face a crisis that required it to treat workers with a modicum of humanity. So we have images such as J. Howard Miller's "We Can Do It!" poster made during the Second World War, which glamorizes the wartime factory service of women, who filled in for men who were fighting the Axis powers. And there are images made by progressive artists to assert the inviolable humanity of workers, no matter how exploited and brutalized by the economic forces arrayed against them, including Dawoud Bey's powerful and melancholy images of small shop owners in Harlem made in the 1970s.

But in several images, we also have telltale signs of the true status of the American worker, beguiled by promises of rising prosperity, seduced into the fiction that work is essential to our humanity, traduced by greed and disempowered by the close alliance of politics to commerce. Trash, seen in the foreground, becomes a visual metaphor for the worker as entirely expendable. One sees it in the crumpled paper on the pavement in front of Henry Inman's 1841 "News Boy" and in the oyster shells and discarded newspaper in John George Brown's 1879 "The Longshoremen's Noon." In a haunting photograph by Hine, made around 1910, a small, barefoot girl in an orphanage makes the connection explicit: She is in the foreground, almost tipping into our space outside the image, and she is grimy, vulnerable and forlorn, a social castoff. A quarter century later, Edward Weston photographed a cement worker's glove, cast off, torn and covered in solidified grime. The worker isn't even present. Someone has taken out the trash.

It's hard to locate any golden age of the American worker in this exhibition. The early days o f the independent artisan-patriot, seen in Pat Lyon's portrait, were brief, if they ever existed at all. Images of workers during the postwar boom years of the 1950s and 1960s must be seen in the context of those who didn't share in the upper mobility, the migrant farmworkers who put the iceberg lettuce on the Formica tables and the street sweepers and janitors who swept up the McDonald's wrappers and mopped up the ketchup spatters.

And what of our new age, this precipice on which we stand and wait for automation to displace the teamsters and taxi drivers and waiters and cleaning staff and fry cooks and fast-food workers and bank tellers and all the rest of the last residue of the old blue-collar class? And what of disruption, this idea celebrated by our new oligarchs as essential to progress, but which amounts only to more destruction of community and more disintegration of family life for so many people?

In his assembled sculpture, "Nine to Five," artist Josh Kline shows us a janitorial worker printed in 3-D, dismembered and jumbled up with his cleaning brushes and detergents and Lysol bottle, a perfect dystopian image of the future. Sam Comen shows us an army of farmworkers, wooden poles in hand, about to savage the almond trees of California for the last of the harvest. Perhaps someday they will carry more than poles, but in service to what? There are intimations of anger and even rebellion in some of the last images of this exhibition, but anger is merely a force, not an idea, and it is easily co-opted and misdirected and put to purely self-destructive uses.

One wishes for some kind of utopian image to end the show, something that says: It didn't have to be this way. Something that reminds us that the market economy isn't like the weather or gravity, a given of the natural world. It could be tamed and made to serve us all better, so that we might spend less of our life working and more of it fully engaged with our true humanity. But that would be naive and a fool's dream. For as long as it was profitable to structure America like a workhouse, we had work. Now that the possibility of mass leisure is upon us, we have unemployment, opioids and death.

The Sweat of Their Face: Portraying American Workers is on view at the National Portrait Gallery through Sept. 3, 2018. For more information visit npg.si.edu.