Word: discoloration
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Dates: during 1960-1969
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...Cleaning. The unwholesome mess that U.S. citizens and corporations spew into that great sewer in the sky costs them dearly-$11 billion a year in property damage alone, according to the Department of Health, Education and Welfare. Air pollutants abrade, corrode, tarnish, soil, erode, crack, weaken and discolor materials of all varieties. Steel corrodes from two to four times as fast in urban and indus trial regions as in rural areas, where much less sulphur-bearing coal and oil are burned. The erosion of some stone statuary and buildings is also greatly speeded by high concentrations of sulphur oxides...
Freedman emphasized that haste is of extreme importance in such work. If stains are allowed to dry, they may permanently discolor an object...