Research into methods of cleaning silicate sandstones used for historical monuments

Abstract

The cleaning of monuments ranks among the most critical processes in monument restoration, both from an aesthetic and a technological point of view. This article deals with research into the cleaning methods used for the removal of soiling firmly sticking to fine-grained silicate sandstones. The work contains petrological characterization of the substrates and the modes of soiling deposited on the surface. For the cleaning tests, two types of laser have been used (Q-switch and short free running), micro-abrasive cleaning using two different abrasives, and chemical cleaning based on ammonium fluoride. The effects of fluency, frequency, pre-moistening, and the type of device have been examined within the laser cleaning tests. These results have been compared with the results of the abrasive cleaning and chemical cleaning tests from the point of view of sensitivity to substrate, cleaning efficiency and rate of controllability. To evaluate the tests we have used a visual examination of the surface, microscopic examination of the surface and polished sections, and electron microscopy. After the cleaning tests, the changes in the physical properties of the surface were examined.