Introduction

In 1992, after being displayed outdoors in an urban-industrial environment for over 60 years, Philadelphia’s version of Rodin’s The Thinker showed the effects of "acid rain" and particulate deposition common in such atmospheres. Streaking, caused by the run-off of condensate from the sculptural forms, had etched a pattern of irregular rivulets in the surface, while urban aerosols from industrial and vehicular sources built up black and other accretions.

The forms were obscured; Rodin’s modeling could no longer be "read," with some high points black and recesses bright due to corrosion.