The Richter Window – Gerhard Richter's Window in Cologne Cathedral

The site originally held windows from 1863, a gift of the Prussian royal house to the cathedral. They depicted secular and Christian rulers and came from the Royal Institute for Glass Painting in Berlin-Charlottenburg. Destroyed in the Second World War, they were replaced in 1948 by a plain ornamental glazing by Wilhelm Teuwen. This later needed renovation; because it lacked colour, the incoming light dazzled and was felt to be disturbing.

From a palette of 800 colours, Richter chose 72 tones resembling those found in the cathedral's medieval and 19th-century windows. One half of the surface was arranged by a random generator; on the other half the squares are fixed by mirroring, so that lanes 1 and 3, 2 and 5, and 4 and 6 each mirror one another. Richter intervened in a few places, for instance where a supposed image such as the numeral "1" might have appeared. On his restraint he said: "I held myself back rather. I wanted the window to have something self-evident, something everyday; in any case it should not become a 'riot of colour'. Not too warm, not too cold, reserved, as neutral as possible." The roughly 11,300 mouth-blown glass squares were not held by lead cames but laminated onto safety glass with narrow black silicone strips, so the colours interact without dividing lines.

Gerhard Richter worked without a fee. Those responsible for Reims Cathedral were also interested in a Richter window; after he declined, the artist Imi Knoebel was commissioned there instead.