Met History wrote:

>
> Brick Presbyterian Church, 1939 by York & Sawyer is a muscular red
> brick new england meeting house on 91st and Park Avenue.    The
> building was cleaned recently, bringing out the crisp limestone
> carving very nicely.   But the slate roof is quite visible for blocks
> around.  The slate was not cleaned, is streaked and discolored.
>
> So, has it come to this, Shaman?  We need to clean roofs now, too?
>
> christopher

Sharpshooter,

With tooth brushes.
Been there, done that, don't want to go back.

For those beyond the Hudson, the air got cleaner some time ago, jut
nobody cleaned the roofs of the last centrury + .50.
I can imagine that suddenly the slate roof would look dirty once a stone
facade below is cleaned.
Does anyone need to do anything about it... well, not really -- change
the aesthetic perception of the dimwats and leave it alone.
Cleaning of buildings in many cases is a capital indulgence, unless
attached to a more extensive maintenance program, done for the show of
being able to do it.
Then again, cleaning the marble roof at Federal Hall of WTC debris is
serious business not to be snuffed at. A whole bunch of dust, loose
stationary, receipts & business cards.

][<

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