THERMAL ANALYTICAL INVESTIGATION OF DIFFERENTIAL SURFACE WEATHERING ON INDIANA LIMESTONE: A STUDY OF THE MICHAEL LANTZ SCULPTURES: FEDERAL TRADE COMMISSION, WASHINGTON, DC

摘要

Two Michael Lantz sculptures (1942), located at the Federal Trade Commission in Washington, DC were examined in order to determine the cause of differential surface weathering on the limestone substrate. The sculptures are composed of Indiana limestone (Salem deposit) and have in unprotected, areas lost approximately 1.5mm of calcite cement, leaving fossil shell fragments exposed on the surface. The sculptures exhibit staining along zones that define a gradation in greater and lessor weathered surfaces. A precipitate (>lmm thick), has been deposited in these zones. The sculptures have been exposed to a weathering environment for 56 years and there are no records indicating the use of acidic or alkaline cleaning materials. Black surface deposits have altered the visual characteristics of these important works of art. The present investigation is directed toward a better understanding of differential surface weathering on Indiana limestone sculptures exposed to an urban environment. Collected specimens are investigated by Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA). Optical microscopy and digital photographs of the sculptures are shown to be valuable investigative tools for sculptured surfaces.