The removal of dirt, deposits, patinas and encrustations, consisting of materials unrelated to the stone surface or of the artefact of historical and artistic interest, or products of the original material that are irreversible and harmful for their conservation, may be carried out using mechanical/physical or chemical methods.
The cleaning process must be:
– well controllable in every phase, gradable and selective
– must not produce materials that are harmful for stone conservation (eg: soluble salts)
– it must not produce modifications, such as micro-fractures or strong abrasions on the clean surface, which can accelerate the deterioration due to increased porosity