From the start, Wolfgang Tillmans' (born 1968) abstract photographs played a decisive role in his gentle subversion of photographic hierarchies and his seductive emphasis on the materiality of photographic objects in his presentation of them. In the past decade he has pursued this tack, making wholly non-representational photographs that explore processes of exposure. From the delicate veils of color in the Blushes and Freischwimmer series, and the sculptural paper drops made of folded or rolled-up photographic paper, to the colorfully compelling works of the Lighter series, the printed object itself, divorced from its reproductive function, is always the point. For me, the abstract picture is already objective because it's a concrete object and represents itself, Tillmans says; the paper on which the picture is printed is for me an object, there is no separating the picture from that which carries it. That's why I like to show photographs sometimes framed and sometimes not, just taped to the wall. Designed by the photographer, and with 275 color reproductions of these works, Abstract Pictures --now in paperback--impressively demonstrates how fruitfully Tillmans has mined this terrain.