Читать книгу Monument Future - Siegfried Siegesmund - Страница 421

There are different cleaning methods: the choice of the same must be from time to time, through laboratory tests, based on the nature of the substance to be removed, the type of surface and object to be cleaned, the nature of the stone material, the type and of the degree of alteration. It is therefore clear that cleaning involves both extremely delicate aesthetic and technical problems that only a specialized technician can solve.

The cleaning techniques most frequently used in the stone conservation sector can be distinguished in chemical, mechanical or laser methods.

In general terms, the cleaning of a historical monument should meet minimum requirements such as: 1) the absence of harmful products which, remaining on the stone, could compromise its future conservation; 2) a cleansing action that does not produce surface irregularities, micro-fractures, increase in porosity, dissolutions, mineral transformations or colour changes in the original material; 3) a sufficiently slow action over time to allow the operator to continuously check the degree of cleaning and stop the operation at the desired time; 4) moreover, they must be gradual and selective processes with affordable costs. (Pozo-Antonio J. S., et al. 2016), (Turk, J., et al. 2019), (Gulotta, D., Toniolo, L., 2019), (Perez-Monserrat, E. M. et al.), (Doehne, E. F.; Price, C. A., 2011).

In this research, only micro-sandblasting was evaluated as it is a recommended technique for cleaning all types of natural stone. Unlike water-based cleaning techniques that are usually applied in the conservation of buildings without historical and artistic interest, dry systems are suitable for the cleaning of stone monuments, in particular those covered with atmospheric particles and other crusts. The use of regular sandblasting is accepted only in certain circumstances, for example on large stone surfaces and on areas without any artistic or historical interest, due to its high aggressiveness caused by high pressure and high hardness of the projected sand (Pozo-Antonio J. S., et al. 2016).