Laser versus scalpel cleaning of crustose lichens on granite

•Lichens were cleaned with a Nd:YVO4 laser at 355 nm.•Covering level of the thallus and colour influence on the laser cleaning effectiveness.•Laser caused mineral damages, mainly on biotite.•Laser achieved better cleaning of lichens than scalpel.•Scalpel followed by laser offered better results than these procedures alone.•Colour spectrophotometry cannot be used as a reliable tool to assess the cleaning effectiveness.