For technical advice, articles, an extensive bibliography, web links and much more relating to the use of natural stone, visit:
resource
n. a supply or source of aid or support; something resorted to in time of need.

Water, poultice (poulticing can be used to remove dirt and pollution from stone surfaces. A variety of solvents or other active ingredients are held against the surface to be cleaned in a poultice of cellulose pulp and sepiolite), JOS & DOFF cleaning systems