I  was just in Paris an observed the cleaning of Notre Dame ; truly remarkable
results; the stone absolutely had a glow about it. However the day I visited
the job site a scathing report about the cost overruns and the time it was
taking to complete was front page news. The entire Lourve was cleaned in a
little over a year with Gommage( micro abrasion neutral powders ) Notre Dame
is still on the front facade at three times the expense and time. Im not sure
it will be popular with budget managers..lovely lovely results though. Regards
Michael Davidson