Urban Hospital — Kreuzberg, Berlin

Four stacks stand against a wall of exposed-aggregate panels, each capped with a round grille, all the same height, evenly spaced. A diagonal of sun crosses the wall behind them and clips the first two. Nothing else happens in the frame.

What held me here was the blue. It was already on the pipes; I only pushed it a little. Everything else in the picture stays grey — the panels, their joints, the cobbles — so the colour is not spread across the surface but locked inside four objects. It behaves less like paint on a building than like something set down in front of one.

Service equipment on the least photographed side of a public building. Nobody designs a ventilation stack to be looked at, and nobody moves one either — they stand where the plant needs them, which is why the spacing is as regular as it is. The picture takes that accident of engineering and reads it as composition.

Ventilation stacks on the Klinikum Am Urban in Berlin-Kreuzberg, the only hospital in the district: Peter Poelzig’s reinforced-concrete complex, begun in 1966 and opened in 1970, the first municipal hospital built in Berlin after the war. Part of Fremde Fassaden, an ongoing series of colour-shifted façades made in Berlin, with detours to Duisburg, Visby and Douglas. See the other works made in Kreuzberg.