The photogram is a footnote in the history of Modernism, writes Andrew Mead. In the 1920s, harking back to the origins of photography, Man Ray and Moholy-Nagy placed objects on sensitised paper, which they then exposed to light. Contours, shadows and textures duly combined to make abstractions without a camera.
At Kettle's Yard, Susan Derges reinvents the photogram, working at a much larger scale than her 1920s predecessors. When night has fallen, sheets of light-sensitive paper, 1.5m to 2m long, are placed underwater in trays, either on the bed of the sea or in Devon's River Taw. The latter may be in full spate, frozen over, or diminished by drought - Derges makes capital from perpetual change. A brief exposure to flashlight captures both a moment in the river's flux and the ambient conditions - moonlight falling on the water, perhaps, or traces of human presence (Derges and her assistants).
Some of the resulting photograms speak directly of these aqueous origins: of ripples and eddies, or the angular geometries of fractured ice. But they tend to slip loose from their literal moorings and live as metaphors. One work at Kettle's Yard, intricate and multicellular, is like a microscopic section through an organism. Others are reminiscent of aerial views, the satellite's eye on the world - a reading encouraged by their tendency to comprise two unequal parts, with an irregular coast-like line as the divison.
In the gallery's double-height space, the images are pink, purple, violet in hue. The four-part 4.9.97 (right) has real grandeur, recalling Abstract Expressionist paintings in search of the sublime.