Environmental effects

The environmental conditions surrounding the Sargent murals throughout their history explain many of the changes that have occurred. Pollutants such as dust, grime, and soot from nearby trains substantially darkened the mural surfaces. Fluctuations in air temperature contributed to the cracking and flaking of paint. High levels of relative humidity also enabled pollutants to bind tightly to the mural surfaces.
Israel and the Law, detail showing heavy buildup of grime and dust on paint surface (1999 photo)
The Triumph of Religion