DOWNTOWN

Donal Lumbert’s art has undergone an upheaval. His formerly flat, earth-on-aluminum abstractions that suggested aerial views of desert terrain have surged into high reliefs that closely emulate boulders. These rough-textured “rocks” jut out as much as two feet into the room and occupy up to 54 square feet of wall space. They are made of polyurethane foam, covered with sand and stained with earth and pigments.

While Lumbert’s earlier work insinuated itself into memory through a subtle tension between art and nature, the new pieces play a more assertive game. They vigorously announce themselves as natural forms, then back off and remind you that they are really paintings. It’s hard for art to have it both ways, but Lumbert’s balancing act is what makes his current effort interesting. He successfully weighs the drama of diagonally tilted boulders that might have been excised from stone cliffs against gentle nuances of natural-looking blue-gray or rust-red washes. Surfaces are at once painterly and natural looking, a fact that re-creates the artfulness of nature.

That Lumbert insists upon mounting these massive stone-like forms on sheets of similarly treated aluminum at first seems distracting. Yet, as you imagine the reliefs without their protruding corners, you realize that the flat backing removes the work from geological wonder and grounds it in aesthetics. (Ovsey Gallery, 705 E. 3rd St., to April 20.)