This afternoon trip in downtown Washington, D.C., will permit study of pollution, structural, and other kinds of damage to structures with emphasis on those constructed of fine- to coarse-grained marble but with representatives of limestone and red sandstone. The tour will include in order of examination [date of work initiated (i) and/or occupied (o.) and stone type]: the Renwick Museum (1859o., red sandstone trim replaced 1987), Corcoran Museum (1879c. enlarged 1927, coarse-grained marble), two Red Cross buildings (1915i.-1917o., 1927i., fine-grained marble), Memorial Continental Hall of the Daughters of the American Revolution, DAR (1904i.-1909o., fine-grained marble), Pan American Union Building (1908i.-1910o., coarse-grained marble), Constitution Hall (DAR) (1929o., limestone), Washington Monument (1885o., marble), Jefferson Memorial (1943o., exterior of fine-grained marble), and Lincoln Memorial (1922o., very fine-grained marble). Coarse-grained marble is normally more resistant to pollution damage than fine-grained marble. Direct exposure to the elements hastens degradation. The most severe pollution damage occurs to balustrades and columns: runoff from bronze onto fine-grained marble can also cause serious degradation. Any sort of overhang tends to protect the underlying stone, but exceptions will be seen at the Jefferson Memorial. In general, vertical |