I’ve barely seen a stranger’s face in a year, just masked figures roaming the streets, distinguishable by a hair-do or a distinctive slouch. That might explain the frisson I felt seeing all the maskless mugs in Alice Neel: People Come First, the Metropolitan Museum of Art’s tribute to the 20th-century’s pre-eminent portraitist. They glare, stare, mull and pout, so many naked features it feels illicit to be among them, like having sneaked into the kind of large gathering the authorities are always prohibiting.

The exhibition is an exciting, though not especially comfortable, place to spend an afternoon. “Randall in Extremis” could almost be a warning against going barefaced, the corpse-like head a mélange of blood-red, mud-brown and industrial grey blotches, the teeth jagged and feral, round eyes awry.

Neel, who died in 1984, was a virtuoso at whipping away the kind of shield that most of us wear even in the absence of an airborne germ — carefully composed attitudes of indifference, pathetic defences we mount against our own eccentricities. She performs that surgical removal with tenderness (sometimes), clinical aloofness (often), and at times even predatory passion. The critic Lawrence Campbell noted that she “seems to detect a hidden weakness in her sitters which she drags out, yelping, into the clear glare of day”.

The Met takes a narrow view of Neel, portraying her as a radical humanist, brimming with politically charged empathy. The curators make much of her choice to live in East Harlem as part of her life-long campaign against poverty.

They position her within the convulsions of her moment (which are ours, too), emphasising her critique of sexism and her support for civil rights. The texts and catalogue essays draw a line from her political beliefs to her art. And it’s true that she gravitated toward the angry, the vulnerable and the victimised, stabbing at injustice with every stroke of her brush. At the same time, though, this brawny, abundant show overwhelms its organisers’ bland affirmations. Neel’s irreconcilable complexities blow past any attempts to contain them.

Her gift was formidable, supercharged by tenacity. She offers us Georgie, a boy she’s painted several times before; he practically grew up on canvas, the way today’s toddlers are already practised Instagram posers. Now he’s on the border of manhood, a phallic knife jutting from his lap, his hair coiling into a tower. Two vertical strokes on his forehead denote the creases of a frown. The torso is torqued, ready to spring. Neel claimed to be unimpressed by the weapon. “He had a rubber knife and used to pretend to cut my throat,” she recalled. “This was just fun and games.” And yet this unsettling work portends a dark future: two decades after it was painted, Georgie was convicted of a double murder.

As in so many of her portraits, sympathy, detachment and ferocity intertwine. Neel likened her life’s project to Balzac’s multi-novel portrait of society La Comédie humaine, in which the author taxonomised humans the way entomologists classify bugs. Neel’s version is La Comédie newyorquaise, a loving yet cool ethnography of her city. But alongside the scholar in her soul, a hunter lurked, too. Neel was enthralled by the people who visited her home and arranged themselves before her easel. She chattered while she swept the canvas with dark outlines, disarming her sitters, desultorily waiting to pounce. Then, she gorged herself on her subjects’ vitality. When they left, she felt depleted.

She insisted on the timeliness and almost journalistic precision of her art. “People’s images reflect the era in a way that nothing else could. When portraits are good, they reflect the culture, the time and so many other things,” she said. It’s true: you can almost date the picture to within a year or two, just by examining the hair and clothes.

And yet the New York she feasted on remains intact. In 1962, Neel moved from East Harlem to West 107th Street and Broadway, a corner I walk past several times a week. I recognise the “Cityscape” she transcribed from her window: the strip of snow-streaked median where West End Avenue begins, the heavy stone facade of the building on the far side of Broadway, and the blaring sign on the corner of 108th Street. (It read “Bar” then; now it’s a Chinese restaurant.) I have stood on the same spot she did on Riverside Drive, watching the same wavering, candle-like sunset, with its lurid, Munch-ian hues.

That sense of permanence and solidity pervades her work, and it makes her ideals and zeitgeist-grabbing aspirations matter a little less with every passing day. Despite herself, she was a painter of classics. People rarely smile in an Alice Neel portrait. Whatever their class or social background, they share an affectless melancholy, a contorted discomfort in the world. They hoist a heavy burden.

“Richard in the Era of the Corporation” portrays one of her sons in a suit, tangled up in his own limbs. His hair is a shiny helmet, his face and hands tinged grotesquely green. A text tells us his mother disapproved of his work for Pan Am because of her belief that capitalism was dehumanising, and the image reflects that critique. (Richard was a fan of Richard Nixon’s, whose name Neel forbade him to utter in her presence.) Yet she also used paint to articulate a more unbridgeable separation between them than the one carved by political disagreements. Her interest is as much in the chasm itself as in the man on the other side.

Neel recognised that she saw her poor neighbours from a distance, through the lens of relative privilege. “I enjoyed the luxuries of the rich, but sympathised with the poor,” she confessed. “I always loved the most wretched and the working class, but then I also loved the most effete and most elegant.” Only a nice bourgeois lady could be so profligate in her affections; only a great artist could manage them with sensitivity and aplomb.

In one of the exhibition’s most arresting images, a woman cradles an ailing infant in her lap. The picture splinters into discordant fragments: her gentle, smiling face, so at odds with the bluish breast thrusting from her dress; the struggling baby, vainly gasping for nourishment; the child’s enlarged genitalia; the mother’s fingers, spread like a giant squid across her knee. There’s sympathy here, but also something darker. The woman is Carmen Gordon, a Haitian housekeeper who sometimes also worked for Richard’s family: an employee, in other words, partially unclothed and at the painter’s mercy. The picture’s disequilibrium mirrors the painter’s discomfort at the power relationship between observer and observed.

Neel finally resolved that tension in a late tour de force, a merciless self-portrait of the artist at 80. She is nude and battered by time and experience, with sinking breasts, splotchy legs, and a torso shaded in bilious green. It’s a courageous move for a life-long student of foibles to open herself up to the impassive scrutiny of others. Like Carmen, she is also monumental and charismatic, a presence who challenges viewers to look away, to dismiss all that she has seen and all that she knows.

To August 1, metmuseum.org

All photographs from The Estate of Alice Neel

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