A lot of art materials are pretty icky, and it hardly requires a dedicated Freudian to note that, in their raw form, clay, paint, and glue are not without an excremental quality. The physical nature of artistic media, the mess of an artist’s studio, and the feel of handling materials not fully transformed into something else are at the heart of William J. O’Brien’s recent sculpture. O’Brien, like Robert Rauschenberg or, more recently, Nancy Rubins, Jessica Stockholder, and Jason Rhoades, has a light touch, making assemblages that seem at once tenuous and inevitable. O’Brien’s aesthetic is one