For followers of abstract art, this summer is shaping up nicely. Several Chelsea galleries have mounted or announced group exhibitions considering abstraction from various angles. Two now on view scrutinize materials: “Substance & Surface” at Bortolami Gallery, and “Stubborn Materials” at Peter Blum Chelsea. Taking divergent but not-quite-irreconcilable positions regarding the most convincing approach to thesubject, their selection of work is guided by entirely different sets of assumptions about what materials are for, and what they should or should not be allowed to do. Taken together, the exhibitions reflect the dual nature of the art object: a marshaling of physical matter, and a metaphor for imaginative space.

“Substance & Surface” features work that wears its materiality on its sleeve. The work enlists the inherent qualities of the chosen materials — stuff like carpet, tar, and sand — favoring the concrete and opaque over the atmospheric and transparent. The show’s touchstones are vintage works by Piero Manzoni and John Armleder. One of the series of works that marked this erstwhile landscape painter’s foray into uncharted Conceptualist territory, Manzoni’s “Achrome” (1959), a small, whitewashed relief in gravel on board, resolutely signifies nothing but itself. It is what it is, a literalistic reaction to the Romantic overlay enlisted throughout the previous decade, from Pollock to Dubuffet, to justify a robust engagement with materials.

Mr. Armleder, who has connections to the Fluxus group, has for many years tested distinctions between art and life. His work from the 1980s elides painting and other classes of nearly two-dimensional objects, such as tabletops, electric guitars, and carpets, by simply hanging them on the wall. “Untitled” (1984), a 4-foot square expanse of pegboard coated in drab, greenish lacquer, does the same for construction materials. With a nod to Duchamp’s readymades, it mocks both the tiresome grids of Minimalism and the retinal jitter of Op.

A strategy common to all of the works here is monochrome, which precludes the depiction and narrative that proceed from figure/ground relationships, as well as the suggestion of space created by interacting colors. The viewer is greeted by Eric Wesley’s imposing, improbably handsome “Spa-chrome 1-6” (2007), in which misaligned grids of bland floor tile jiggle against one other but hold their anti-illusionistic ground. Mike Kelley’s “Carpet 7” (2003) defies the viewer’s reflexive attempt to locate an image somewhere in its broadly white-scumbled blue shag. Glenn Ligon’s “Study for Stranger #26” (2006), in coal dust, oilstick, and canvas, features barely discernable, stenciled lettering. The artist’s recent work culls passages from James Baldwin; the literary substance of this piece is illegible, subsumed by its fetching, gun-metal gray surface.

“Stubborn Materials” is curated by the director of Peter Blum Chelsea, Simone Subal, who favors abstraction with a poetic twist. Here, materials are transformed and transcended. The artist team of Jonah Freeman/Michael Phelan channel the Chinese tradition of the scholar’s rock, or “gongshi,” in a trio of silvery, blown-up scans of crumpled aluminum foil from a series called “Reynolds Wrap Aluminum Foil” (2007). The works’ shadowy creases suggest entangled groups of figures. Refitting Modernist “truth to materials” to the digital era, the artists assert that a given material has numerous truths.

Dangling on fishing line from modified ceiling fans, a swarm of what could be sweepings from Richard Tuttle’s studio floor — bits of tape and paper, plastic beads, rubber bands, a Band-Aid — whirls past the viewer in a kinetic work by Larry Bamburg titled “[ ]” (2007). In assemblagist Ian Pedigo’s “Decentering, Reversibility” (2007), a coiled, blue felt blanket props a slab of honey-colored, foil-faced insulating foam. A pentagon of appropriated magazine photos of leisure-time activities infiltrates this hybrid of found formalism. “Smithson” (2007), by Rosy Keyser, in enamel, vinyl, and reflectors on canvas, incorporates recognizable imagery differently. Taking color cues from the jungle greens on the cover of a 1970s-era Smithsonian Magazine, the artist masks just enough of the image to extract its inherent abstraction.

Jutta Koether’s work is generally uneven, but she has two solid pieces here. “Plein Air #4” (2007) is on 9-foot-wide unstretched canvas, stapled to the wall. From frantic, feathery washes of black paint emerges a murky, mysterious space. “#3” (2006) is a small, inverted isosceles triangle about an inch thick, covered with black paint and a hard, smooth skin of “liquid glass,” or sodium silicate. It’s a great-looking material, but Ms. Koether has used it often, and she should find a new hook. Visually severe, obdurately resistant to association, this reticent work would not be incongruous in “Substance & Surface.”

“Substance & Surface” until August 31 (510 W. 25th St., between Tenth and Eleventh avenues, 212-727-2050);

“Stubborn Materials” until August 25 (526 W. 29th St., between Tenth and Eleventh avenues, 212-244-6055; NB: The gallery will be closed the first three weeks of August).