Assessing the Deterioration of Pennsylvania Marble in William Strickland's Mechanics' Bank
Historic Preservation and Conservation
Pennsylvania marble, a moderately metamorphosed and polishable calcareous stone, was the most desirable building material in early-nineteenth-century Philadelphia, gracing structures that ranged from federal institutions to hundreds of rowhouse stoops and grave markers. While changes in architectural taste and a poor performance under pollution made it an obsolete material by the early twentieth century, its major role in the historic fabric of the city justifies research into its deterioration and conservation. The Mechanics’ Bank was erected on Philadelphia’s Third Street in 1837 by William Strickland, one of the country’s leading Greek Revival architects. The marble-clad Corinthian building is, in spite of its small size, one of the finest structures built in the city in the early nineteenth century; however, a history of private ownership and frequent changes in use has resulted in very little research on the building and scant, poorly documented, and often misguided maintenance. This thesis seeks to document the marble façade of the Mechanics’ Bank and gain an understanding of its micro- and macroscopic behavior through condition surveying and mapping, non-destructive evaluation methods, and laboratory analysis of samples including polarized light microscopy. The knowledge gathered through these means will be used to establish hypotheses for the causes of deterioration; compare the building with other Pennsylvania marble structures in Philadelphia; and test and refine previous findings on the relationship between the microstructure of Pennsylvania marble and its performance.