Rodin’s The Thinker at Philadelphia: A treatment using chelating agents

Andrew Lins


Situated on a very heavily trafficked parkway in the center of the city, The Thinker at Philadelphia’s Rodin Museum is a prominent local landmark. In 1991, its deteriorating condition necessitated conservation intervention, prodded by negative comments about its appearance from the public. A treatment plan was undertaken with direction from the curatorial staff and in consultation with local conservation groups. The goals of the treatment were: 1) to re-establish the sense of the modelling, which had been undermined by the accumulation of black accretions on the high points ofthe figure and streaking from acid rain run-off, and 2) to return the sculpture – as far as feasible, considering the degree of weathering – to a patination in keeping with the artist’s original intent, based on historical evidence and extant patination.

A survey of the condition and previous conservation treatment of other Thinkers in the USA and in France was carried out, including on-site inspection where possible and photography. Molds were taken at two positions on the sculpture in five different sites (Philadelphia, Paris, Columbia University in New York City, Detroit and Baltimore); positive casts in epoxy were sectioned, mounted and polished to compare the surface relief from the different environments and treatments. Reproductions of weathered surfaces mimicking the Philadelphia example were made by electroforming, patinated with a variety of layers and colors, and coated with various lacquers and waxes. These preparations were a part of the decision-making process, to allow the curators and conservators the most control and agreement over the net result of the treatment.

After determining a patination and coating system that satisfied the aesthetic requirements of the curators and remained feasible in terms of available conservation time and funds, a series of cleaning tests were undertaken. Our goal was to remove the disfiguring black accretion while retaining as much of the underlying cuprite layer as possible, with the hope of thereby reducing the overall surface relief of the weathered bronze. Of the many current cleaning methods, a variant on alkaline EDTA-based poultice followed by low pressure steam proved the most satisfactory, allowing controllable spot application. The black crust and loose copper sulfate corrosion were largely removed, leaving much of the cuprite layer intact.

Following cleaning, the sculpture was patinated with copper nitrate, followed by ammonium sulfate. A wax coating was applied, a selection dictated by the frequent climbing and occasional graffiti which the sculpture endures from the public.