Tomma Abts is stepping off the canvas for the first time. At the invitation of the Fridericianum in Kassel, the painter is creating a site-specific interior wall painting for the museum's Rotunda — her first work conceived as architecture rather than as an easel painting. The composition answers directly to the room. Beneath the Rotunda's fan-shaped glass roof, a spacious atrium is ringed by a gallery that curves along one side. Working with the space's distinctive volumes and light conditions, Abts has devised four geometric forms for it: a circle, a square, an ellipse and a rhombus. The circle and square will sit on the atrium walls directly beneath the glass roof, illuminated by natural daylight; the ellipse and rhombus take the recessed walls of the surrounding gallery, where artificial light dominates. The pairing is deliberate and characteristically rigorous. The two rounded forms are painted as solid fields, the two angular ones as broad frames, and across the void of the atrium they trade roles as figure and ground. Their arrangement shifts with the changing light through the day, setting up moving relationships between the forms, their shadows and the architecture that holds them. The commission marks a new direction for an artist known for an intensely private studio process. Born in Kiel in 1967 and based in London since 1995, Abts builds her small abstract paintings slowly, layer upon layer, working without preliminary studies and letting each composition find its own form. In 2006 she became the first German artist to win the Turner Prize. Now that same patient investigation of form, colour and pictorial space is being tested at architectural scale, in one of Germany's most historically charged exhibition buildings.