“The Annunciation,” 1898, Henry Ossawa Tanner, Oil on canvas. (Courtesy Philadelphia Museum of Art)

The Philadelphia Museum of Art says that its purchase of Henry Ossawa Tanner’s 1898 “Annunciation” was the first piece by an African American artist to be acquired by a major American museum. Tanner’s dramatic painting, in which a slightly disheveled and fretful Mary cowers before an angelic apparition, is one of the key works in the museum’s “Represent: 200 Years of African American Art.”

The exhibition, which opened Saturday, is smaller than its grand title would suggest and has a bit of a Black History Month feel: a well-intentioned institutional effort meant to demonstrate to local audiences a commitment to diversity, but derived from the museum’s collection and relegated to a relatively small, temporary gallery. But as you dig into it, and begin tracing the connections between its works, the show gathers force. In the century and more since the 1899 acquisition of the Tanner, the museum also has accessioned key pieces by other essential African American artists, giving visitors a rich if synoptic history of trends in American art over the past two centuries. And for a visitor who has followed art, and issues of identity and collecting in Washington of late, the exhibition is particularly intriguing — a foil, of sorts, to some of the more conflicted and problematic shows seen in the District in recent months.

First, take the magnificent Tanner. The same painting helped to anchor a retrospective of his work at the Pennsylvania Academy of Fine Arts in 2012. That show couldn’t help but draw out both the power and weakness of his work: his daring reimagination of old themes and provocative use of gritty realism, but also his sentimentality and bathos. In the current exhibition, which includes two Tanner works, both astonishingly good, there are no mediocre Tanners to drag down the general level of one’s enthusiasm.

Now compare Tanner’s “Annunciation” with another Tanner on view in the Smithsonian Museum of African Art’s “Conversations” exhibition, which juxtaposes works from the collection of Bill and Camille Cosby with works by African artists. The 1894 “The Thankful Poor” sums up the basic aesthetic of the Cosbys’ collection, a portfolio of name-brand works by African American artists that often tend to the insipid. It’s a Tanner, but a rather retrograde one that clumsily reinforces a cherished bromide of Darwinian capitalism: that the poor are happy with their lot — rich in spirit if not rich in fact.

The “Annunciation,” by contrast, is a genuinely unsettling painting, with an almost grubby, underage Mary nervously clutching her hands in front of an incandescent shaft of light. There is no angel, just an abstraction of power and luminescence, and the rich folds of sumptuous blue drapery, which serve both to elevate Mary and empower the artist to flights of painterly virtuosity, have been replaced by defiantly terrestrial wads and rags of brown cloth.

“Untitled (I’m Turning Into a Specter before Your Very Eyes and I'm Going to Haunt You),” 1992, by Glenn Ligon. (Copyright Glenn Ligon/Courtesy Philadelphia Museum of Art, Luhring Augustine and Regen Projects)

The painting is so powerful, and so at odds with cliches of idealized depictions of Mary, that it makes one wish it had been included in another Washington exhibition, the National Museum of Women in the Arts’ “Picturing Mary.” That show focused on Renaissance and baroque images and cut off its purview abruptly in the 19th century. Tanner’s painting would have extended the power of the basic argument of “Picturing Mary”: The humanization of Mary in Western art, which didn’t end with the baroque and, in many ways, becomes even more interesting as one explores its ramifications down to the present moment, when long-standing assumptions about Mary’s race, motives and sexuality are no longer taken universally for granted.

“Represent” reaches back even further than Tanner, to the early days of the Republic, when many African American artists and artisans weren’t able to sign their work, not least because a signature would have demonstrated literacy, and in many states teaching slaves to read was illegal. A rare pot made in 1859, signed by an enslaved craftsman named David Drake, speaks eloquently to this injustice, as well as the incalculable impact it had on erasing African American art during the first centuries of the American experience. Inscribed just beneath the rim of the pot is the date and the name “Dave,” rescuing one artisan from the oblivion that befell countless others.

Another object, a wooden standing clock, amplifies the idea that African American artisanship was hidden in plain sight. Peter Hill, a slave who was later freed, likely made the internal timekeeping mechanism, the case probably was made by a white carpenter and the colorful clock face was imported from England. Here, in one piece, we have a metaphor for the material culture of early America: The finely wrought joinery of American craftsmanship looked to Europe for inspiration while neatly keeping out of view the all-important mechanism of enslaved labor.

About the same time that Hill made the guts of the clock, another artist, the once-enslaved Moses Williams, was capturing silhouettes of a family in Philadelphia. But it wasn’t just any family. The museum is fortunate to own a remarkable moment in the history of American art, a collection of Williams’s black-and-white profile portraits of the Peale family, the illustrious clan of white artists and intellectuals who had an outsize impact on American culture. These are not the most visually stunning works in the exhibition, but they have extraordinary symbolic power, a point of connection between white and black, public artistry and hidden craft, artists who have both names and voices, and those who must work in, or literally with, the shadows.

It is moving to see the Williams portraits in the same space as work by Kara Walker, who has repurposed and reinvigorated silhouettes with phantasmagorical energies, and Glenn Ligon’s 1992 black-and-white painting “Untitled (I’m Turning Into a Specter Before Your Very Eyes and I’m Going to Haunt You).” The Ligon painting repeats the words of its title again and again, in stenciled letters that gradually become so overpainted with black pigment that the canvas is transformed from mainly white space on top to mostly black space on the bottom. The title is taken from a play by Jean Genet, in which black actors don “white face” to enact a trenchant critique of race in post-Colonial society.

Works such as this, and many others in this small but poignant exhibition, put into relief how limited the ambition of the Smithsonian’s “Conversations” exhibition is. Cosby has said that he isn’t interested in “angry” art, which seems to translate into complete indifference to much of the best art made after about 1960. Yet the impression left by the art of Walker and Ligon and other artists of the past half-century isn’t so much anger as a deeply focused intellectual critique. Not only does their work make more sense in this context, but it also sets the older works humming with new energy.

So visitors will likely feel two things after spending time with “Represent”: a sense that this project could have been bigger, wider and more prominently displayed, as well as thorough satisfaction that it has been done so well. It also highlights a fundamental, though often overlooked, difference between curators and collectors. The latter are free to pursue any agenda they like, limited only by the art available for purchase and the means to purchase it. The results can be brilliant, or haphazard, such as in the Cosby collection. Curators, by contrast, tease out, underscore and animate the spaces between art, the threads of connection and intellectual webs that make it possible for artists to keep on creating, keep on extending traditions, arguments and elegies. It may not seem so, at this current moment when the market for new art has become so overheated and crazy, but artists — and Art in general — are better served by intellectual and emotional appetites than by acquisitive ones.

Represent: 200 Years of African American Art is on view at the Philadelphia Museum of Art through April 5. For information, visit www.philamuseum.org.