Larry-

For the brownstone we used Prosoco 766 Prewash, 45 min dwell, with 2:1
Restoration Cleaner, 5 min dwell. For the buff sandstone the treatment was
the same, but the restoration cleaner was repeated twice. The buff still
appears slightly soiled (carbon) but we prefered to underclean rather than
overclean and risk a bleached appearance. The same personnel did the work as
the previous facade.

I suspect in a few years that the difference in facades will be less
noticeable. I also realized today that part of the difference is one of
perception - the sun washes the South face, and the West face is nearly
always in shadow due to surrounding megaliths.

Twybil