Conservation of Rodin's Thinker
In 1992, after being displayed outdoors in an urban-industrial environment for over sixty years, Philadelphia’s version of Auguste Rodin’s Thinker, cast in bronze, showed the effects of "acid rain" and deposits of urban grime. Streaking, caused by acidic run-off, had etched a pattern of irregular rivulets in the surface, while airborne particles had built up dark accretions. Rodin’s modeling could no longer be seen properly. Sculpture conservators at the Philadelphia Museum of Art reviewed options for returning the sculpture to a more acceptable appearance and removing some of the corrosion. Rodin’s writings on the subjects of surface finish and patination were considered. Philadelphia’s Thinker was compared with other casts that had not been exposed outdoors. Conservators performed a variety of tests to determine how best to treat the deteriorated surface and develop a patination that would make the modeling clear again. A series of comparative cleaning tests showed that the most controllable and effective removal of both dark accretions and active corrosion (primarily the basic copper sulfate brochantite) was by use of an alkaline chelating agent (EDTA) in a water-based paste thickened with a cellulose-based powder. The paste was applied, allowed to stand for as little as a half hour, and then removed with water, followed by low-pressure steam. After removal of most of the active corrosion and accretions—up to six applications were necessary on some parts of the surface—the sculpture was repeatedly rinsed with water and dried. It was then patinated in two layers, the first a blue-green layer based on copper nitrate, the second a brown/black layer based on ammonium sulfide. After patination, the sculpture was again thoroughly rinsed with water. A corrosion inhibitor (benzotriazole) was applied using heat, and then a protective coating of wax. Read more on Conservation of Rodin's ThinkerFor more information, please contact the Rodin Museum at (215) 568-6026.
