On the stone surfaces tombstones and artefacts of historical-artistic interest, dirt, patina and encrustations can cause irreversible alterations ofthe original material, inevitably harmful to conservation. They can be cleaned using mechanical/physical methods or by using chemicals.
The cleaning process must be well controllable at every stage,graded and selective, and must not produce materials harmful to the preservation of the stone(e.g.: soluble salts). It also must not produce physical changes,such as microfractures or strong abrasions on the clean surface, that can accelerate deterioration by increased porosity.