Schist surfaces from Foz Coa and Siega Verde archeological sites are covered by a mixture of dfferent lichens, mainly Xanthoparmelia conspersa, X. gr pulla, Caloplaca subsoluta, Lecanora pseudistera, Peltula euploca, Aspicilia hoffmanniana and Pyrenopsis triptococca. Considering the historic value of the open-air prehistoric rock-art, effective, precise, selective and controllable cleaning procedures for the engravings placed on these parks are required. The most effective methods are those with higher extraction of the lichen avoiding any chemical contamination or physical changes in the surfaces, such as grain extraction or colour modification. In this paper, in situ chemical cleanings were performed by means of mixtures with distilled water of ethanol (50% v/v), benzalkonium chloride (3% v/v) and Biotin T (3% v/v). A cleaning with water was also performed as control sample. Moreover, as a physical method, a ns Nd:YAG laser working at 1064 nm and 266 nm were applied. After the cleaning and four years later, the surfaces were evaluated by colour spectrophotometry and Raman spectroscopy.
As a general result, chemical cleanings achieved satisfactory results, while the laser system, regardless of the wavelength used, achieved satisfactory results immediately after the application, but the surfaces started to be recolonized after four years.
Complete tool for submission, evaluation and publication of proceedings for scientific events.
