Dual combination of cleaning methods (scalpel, biocide, laser) to enhance lichen removal from granite

Abstract

Three cleaning methods, namely i) a commercial biocide applied by brush with the subsequent extraction of organic remains by a rod, ii) a scalpel or iii) a Nd:YVO4 laser at 355 nm, single application as well as paired combinations, were tested for removing from a granite two different crustose lichens: Diploschistes scruposus (lighter with a clearly distinguished thallus) and Polysporina simplex (darker with a poorly developed thallus). In addition to the removal rate, side effects such as melting of biotite and feldspar grains and chromatic changes were assessed. The multianalytical approach was based on stereomicroscopy, light microscopy, Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and color spectrophotometry. Combining cleaning methods enhanced the removal efficacy. Biocide followed by laser was the most effective method for removing both lichens colonizing this granite. Mineral melting was more intense for the samples covered by Polysporina simplex due to its lower coverage degree and darker color.