Brudzenie i niszczenie materiałów kamiennych w architekturze zabytkowej oraz sposoby ich czyszczenia

The cleaning of stone materials forming component parts of historical buildings in our times has become the necessity arising, among the others, from the ever- -groving pollution of air. As a consequence, the conservators are facing the two basic tasks: (1) to clean the stone surfaces without any damage brought to them, (2) to protect the stone surfaces against the repeated harmful environmental effects. Mechanisms causing that the stone surfaces become „dirty” are to be handled as a continuous process including the action of several factors and mong them those of chemical character as, for instance, the gaseous contaminations of air by sulphur oxides, those of carbon or nitrogen, the water soluble salts contained in stone and the like. Basing on examples of the stone and brick-built historical buildings in Poznań and in Rogalin, the author listed some methods used in cleaning their buildings with solutions preventing mineralization as, for example, the detergent solution with an admixture of liquid ammonia. For both cleaning and consolidating of stone material hydrogen fluoride solution of clay is also used but when applying this medium the stone needs to be eralder treated with lime water. For filling the losses or restoring the damaged stone material in most cases the following three methods are used: (1) patching (i.e. replacing a portion of worn out stone material by that new in the from of metal, e.g. brass plugs), (2) filling with putties (nowadays prepared from synthetic binders), (3) application of mortars (for coloured plasters and troweled stuccos). However, within in-door parts of buildings for protection of stone materials are highly recommended silicone solutions as they do not affect either the porosity or colour of theirsurfaces. A wide range of works aimed at choosing the most appropriate methods for conservation of historical stone objects is carried out at the National Museum, Poznań.