Joseph Beuys used a rust-proofing product to make his distinctive brown paint, which he called Braunkreuz (brown cross), a German student has found out. Ole Valler of the Hochschule Rhein-Waal made the discovery using x-ray fluorescence analysis on more than 80 works by Beuys in the collection of the Museum Schloss Moyland.

Beuys used Braunkreuz, a matt reddish-brown pigment, on works on paper and sculptures during the late 1950s and early 1960s. He never revealed what was in the mixture, though many suspected it contained floor paint or blood. Now Valler has established that the majority of the works he analysed contained iron, zinc and chromium—components found in rust proofer. The findings are due to be published in the journal Chemie in unserer Zeit (chemistry in our time).

“It is important to know that Beuys used an industrial product in his work rather than an artistic one,” says Barbara Strieder, the head supervisor of the graphic arts collection of the Museum Schloss Moyland. “This shows his belief in the strong connection between art and everyday life. Materials have a special meaning in Beuys’s work.” Strieder also says that the discovery will be helpful for the restoration of works by Beuys and for detecting forgeries.