Imagine the ultimate collection of works on paper from the last two centuries: an ink drawing by Brice Marden, a callotype by Muybridge, a Rauschenberg collage, a Degas charcoal, a Friedlander gelatin-silver print and perhaps 65 pieces of comparable quality. This is the wonderful treat that Fraenkel and Marks have put together for us in the exhibition Open Secrets and the accompanying volume of 70 works on paper in a wide range of media from 1815 to the present. What the works have in common is that they are all "pictures that function as the visible evidence of thinking." Elegantly produced, this catalogue speaks eloquently to the pleasures of connoisseurship.