NEW YORK (NYT NEWS SERVICE).- The best exhibitions tell strong human stories, ones that we might not otherwise know. Such is the case with “Boston’s Apollo: Thomas McKeller and John Singer Sargent” at the Isabella Stewart Gardner Museum in Boston, a small show that’s built around a sensational painting and that has an unreadable relationship at its heart.

The Gardner is, of course, in lockdown these days, and there’s no telling when that will end. But its show is compelling enough to make an impact even at a distance, through online images, a stirring short video and an excellent book, all of which I recommend.

The lead characters of the tale are named in the title, although in an order of importance that might baffle some historians. Surely, they would think, Sargent (1856-1925) should have been listed first. The European-born American was one of the art luminaries of his day, a power-portraitist to the elite on both sides of the Atlantic (Isabella Stewart Gardner was a repeat sitter) who commanded top prices for his attentions.

Thomas Eugene McKeller (1890-1962) was a bellhop and elevator attendant at Boston’s deluxe Hotel Vendome, where Sargent often stayed, and one of the many beautiful men he hired as studio models. Among them, McKeller may have been the only African American. And he was possibly one of the few models of whom Sargent would come to say, in a letter to a friend,“ I don’t know what I shall do without him.”

The two men met in 1916, most likely at the Vendome, when Sargent was visiting from his home in London. At 60, the cosmopolitan bachelor — born in Florence, art-trained in Paris — was in the process of making a career transition from portraiture to the more prestigious genre of architectural decoration. Boston had become the staging place for that change.

In 1890, the Boston Public Library invited Sargent to contribute allegorical murals to its interior. Next came an important commission from the Museum of Fine Arts (the MFA) for mural cycles for the rotunda and grand staircase of its new building. Finally, Harvard University asked him to contribute monumental paintings to its Widener Memorial Library, commemorating student lives lost in World War I. Sargent’s response was yes, yes and yes.

It was for the MFA project that Sargent first hired McKeller. Then 26, McKeller had been born in Wilmington, North Carolina, when the city had had a thriving majority African American population. And he was there, still a child, in 1898 when an explosion of anti-black violence changed all that. There was every reason for him to leave town and he eventually did, making his way to Boston where, after hotel work and a stint in the Army, he took a long-term post-office position, married at 44 and permanently settled down. (There may have been an additional reason for his departure from home. In the exhibition video, McKeller’s great-niece, Deidre O’Bryant suggests that McKeller was suspected of being gay. “To be gay was taboo,” she says, “even within your own family.”)

Sargent seems to have put him to work on the MFA project early on, when its design concept was still developing. Classicism would be the style, elevation the tone in a series of mythological motifs — Apollo and the Muses, Eros and Psyche, Ganymede and the Eagle — interspersed with personifications of the fine arts, including architecture and painting.

A schedule was set and roles assigned. McKeller spent mornings in Sargent’s studio posing, usually nude, as the artist drew charcoal studies of figures, male and female — McKeller posed for both — to be worked up for the final compositions. This was the standard professional routine of the day. A model was considered to be a malleable object — directed to pose this way or that — but, with luck, also a self-expressive one, giving sessions a sense of collaboration.

Judging by the studies he produced for the murals, Sargent found McKeller an inspiring collaborator. Late in his career, he gave Gardner — who had already established the museum — a gift of nine signed charcoal studies from the project, most featuring McKeller’s image. She tucked them away in her files, which is where they’ve pretty much stayed, known but little seen, and never until now shown together. Three years ago, Nathaniel Silver, the curator of the museum’s collection, came across them and decided to make them the pretext for the present show, of which McKeller is the newly spotlighted star.

Some of the Gardner studies are fairly generic: a detached limb, a female torso, bodies seen from behind. But others in which McKeller is clearly depicted are closely observed and personalized. In the allegorical sketch, “Study for Classic and Romantic Art for the Rotunda of the Museum of Fine Arts, Boston,” he stands, nude and lithe, arms raised to his chest, head thrown back, mouth open, as if delivering an aria. It’s a showstopping performance on the part of the model.

Sargent evidently thought so, too. On the same sheet of paper, to the left of his figure, we see a detailed drawing of just his head, with its closely cropped hair, small, delicate ear, and rapt dark eyes. And near the right-hand edge of the sheet Sargent moves in even closer, zeroing in on the model’s open mouth, as if he wanted to get the shape of the lips just right.

And how do we know this is Thomas McKeller we’re looking at? Because Sargent painted a portrait of him which, uncommissioned and untitled, is one of the great portraits of his career.

How, exactly, it came about, or when, we don’t know. It seems to have originated as a study for the figure, in the rotunda murals, of Prometheus, the titan who stole fire from the gods and was punished by having his liver perpetually gnawed by an eagle.

Giant eagle wings still fill the background of the portrait. Although they’re only sketched in (or half painted out), they’ve assumed an accidental function. They now form a feathered aureole framing the extraordinary figure of a nude black man who sits, tensely perched on a pillow, legs spread wide. His brown-gold skin glows. His tilted-back head, with its sparkling skyward eyes, is bathed in light.

It’s a transfixed and transfixing image, sensual, aspirational. And I would say homoerotic. Yet Sargent, who was, publicly at least, tight-lipped on the subject of his sexual orientation, displayed the painting prominently in his Boston studio for years, no doubt as a demonstration of his painterly skill but also, surely, as a tribute to a charismatic man, in whom, and for more than one reason, he took delight.

Interestingly, and frustratingly, this man who was so integral to the creation of the MFA project, is only partially present in the murals themselves. His tautly muscled body is there, repeatedly, in the figures of gods and heroes. Yet all those figures have alabaster-white skin and blond hair.

And one of Sargent’s preparatory drawings, this one on loan from the MFA, is particularly revealing. It’s a study for the rotunda figure of Apollo. We see, side by side, a sketch of McKeller’s head, its features easily recognizable, set next to a carefully drawn image of the head of an antique carved Roman god. In the mural, the Roman head appears atop a whitewashed version of McKeller’s superb physique.

In a catalog essay, art historian Nikki Greene writes of McKeller as a figure “under erasure,” in life and in history, which he was, both as a black man in America and as Sargent’s model.

Theirs had to have been a complicated relationship. Sargent, on the evidence of letters, brought to it a degree of casual racism common at the time. And his portrait of McKeller is, to anyone tuned into the politics of race, unsettling, with its image of a naked black man sitting in precarious balance, his genitals exposed, his hands behind him as if bound.

Several of the other catalog writers — Trevor Fairbrother, Paul Fisher, Erica Hirshler and Colm Toibin — in different ways acknowledge this. And as a kind of foil to this painting, the catalog suggests another one, Beauford Delaney’s 1941 “Dark Rapture (James Baldwin).” The painting itself isn’t in the show but is reproduced in the book.

Delaney (1901-1979), who was African American and gay, left Tennessee for Boston in 1923 and spent six years there studying art. He took classes at the MFA and visited the Gardner often to copy work. He is also thought to have visited the Sargent studio at least once when the McKeller portrait may still have been on view.

“Dark Rapture,” Delaney’s portrait of a teenage Baldwin, shares features with it. The sitter is nude, upright, open-legged, exposed. But he looks grounded and unstressed. His hands lie, relaxed, at his side. He’s alert to us, acknowledges we’re there. And Delaney has made his blackness his beauty, by making his body a prism of rainbow light.

Delaney’s painting was, in its time, a daringly forthright way for one man to look at another, through art, with candid desire. My sense is that the same can be said of Sargent’s portrait of Thomas McKeller, done a quarter century earlier and basically a generation further in the past. In it, Sargent expressed desire the surest way he, as a portraitist, knew how, by making the object of it a star.

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