Effectiveness and durability of chemical- and laser-based cleanings of lichen mosaics on schists at archaeological sites

Lichen mosaics on different-textured schists located in the Coa Valley (Portugal) and Siega Verde (Spain) archaeological sites were cleaned using different chemicals, namely ethanol (50% v/v distilled water), benzalkonium chloride (3% v/v) or Biotin T® v/v), Nd:YAG laser wavelengths (1064 nm 266 nm). The surfaces evaluated 24 h 4 years after cleaning to determine its durability colour spectrophotometry Raman spectroscopy. Unlike lasers, chemicals achieved overall satisfactory results. Cleaning effectiveness, harmfulness of highly influenced by orientation schistosity planes stone; samples, parallel surface contributed a low impact methods absence lichen recolonization. carried out upon devitalization lichens with T maintained longer both sites. • Biocides at 1064 used remove from schists. effectiveness (4 later) investigated. Harmless is planes. ns Nd: YAG (either nm) did not induce extraction. most durable was obtained biocidal devitalization.