One wintry day in 1983, alongside other street sellers in the East Village, David Hammons peddled snowballs of various sizes. He had neatly laid them out in graduated rows and spent the day acting as obliging salesman. He called the evanescent and unannounced street action Bliz-aard Ball Sale, thus inscribing it into a body of work that, from the late 1960s to the present, has used a lexicon of ephemeral actions and self-consciously "black" materials to comment on the nature of the artwork, the art world, and race in America. And although Bliz-aard Ball Sale has been...