In a message dated 3/25/2010 1:35:19 P.M. Eastern Daylight Time,  
[log in to unmask] writes:

efflorescence caused by the use of an acidic wash during  clean-up.


Yeah,  I was thinking of that, looking at the 1923 Pershing Square  
Building, at 42nd and Park.  It is this lovely tawny masterpiece of mottled  buff, 
yellow and brown brick, which to my eye got sort of burned in a  cleaning.  
Do buildings ever recover from that?   c 

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