Catherine Yass

Catherine Yass' recent exhibition 'Descent' comprised one film and two light boxes. As the film - also titled Descent (all works 2002) - begins, to the left of the image we see the uncompleted framework of a building, to the centre and right, an illegible white expanse. Visual information enters at the top edge of the frame and disappears at its bottom. As the camera ascends, it reveals to the left a sequence of receding half-constructed spaces. One light twinkles through the opaque whiteness, which gradually disperses; only at the moment of its disappearance does it become apparent that the whiteness is fog. To the right, a grid of green windows makes us realize that the space into which we are looking is a gap between two skyscrapers, which we seem to be travelling perpendicular to. The structure to the left begins to look more complete, now walled with white metal planks. This is strange, for how could this building stand if those floors at its top end were heavier than those we saw earlier at its base? The answer quickly becomes apparent: at the top of the frame a horizon emerges - the street. Only now does it become obvious that the film has been projected backwards. But it's bewildering, for how could the street be at the top of the frame and how would the workmen walking along it be moving forwards? No, the film is being shown in the same sequence as it was made: during filming the camera was on a platform being lowered by a crane. Yass then rotated every frame by 180 degrees. By the end you feel inverted; as if your head might crash into the ground.

During the late 1960s artists using film would often make one aspect of their apparatus their subject to examine the specificity of their medium and make transparent their working process. Descent recalls Michael Snow's Back and Forth (1968-9), whose subject is the ceaseless panning of the camera, and Richard Serra's Hand Catching Lead (1969), where the descent of the frame through the projector gate is doubled by the image of pieces of lead falling through his grasp. Yet Descent exceeds this Structuralist paradigm. There are too many inversions for them to make sense, for the film's structure to become transparent. The dense fog seen at its beginning stands for the opacity that is the content of this film in which sense is pulled apart, slowly.

It is this pulling apart that characterizes Yass' approach to the medium, and that gives unity to her work in film and photography.

The lightboxes here were produced in the same way as all Yass' lightboxes to date: the transparency at their front is a composite of two photographs of the same subject taken moments apart, one processed as a negative and the other as a positive. Yass' portrait subjects often move between two shots, but here the support holding the camera descended during exposures. The images read like Richter paintings, with scratches of intense red and blue streaking down them. Imagine that cliché of urban photography the motorway at night. Long exposure keeps the road totally legible, but renders cars as streaks of light, connoting 'speed'. Here streaks of colour are the index of stationary buildings: all that is solid melts into light. One light-box (Descent: HQ5: 1/4s, 4.7a, 0mm, 40mph) is dark, with distant elements in relative focus (the City of London skyline) and nearer details virtually illegible. The other (Descent: HQ5: 1/4s, 7.2a, 0.2mm, 20 mph/180a) is much lighter and more abstract since the negative has been inverted; here the pulls of colour look like beads or trails of drops. Like through a rain-washed window, the view on to space beyond is all but blocked by the surface. In both light-boxes the vertical colour streaks warp our sense of space. Viewing them is a vertiginous experience: at one moment their surfaces seem to be concave, bowing away from us both horizontally and vertically, then they flatten out again.

Does Yass' concern with the medium come at the expense of reflecting on the very literal support of her cameras - a corporate building site? Is it possible now to look at skyscrapers without imagining their destruction? Criticisms of the work's abstraction would miss how politics might inform an approach to process and the medium. The view from the World Trade Center was as astounding as the speed of ascent from street level. This too is the upward speed of capital. Yass' works exchange ascent for descent and speed for disorientating slowness. Literally, it takes eight minutes to see her film; metaphorically, slowness here is in the gradual pulling apart of time, space, sense, of media.