Determination of damage thresholds to prevent side effects in laser cleaning of pliocene sandstone of Siena

Effect of laser cleaning on granite color

“…Irradiation on wet surfaces usually decreases the probability of thermal and mechanical damage and also increases the efficiency of cleaning. 1,13,14 The chemical and mineralogical composition of the materials affects the absorption to laser radiation and therefore possible chemical and physical changes and their concomitant color-related behavior. Color is one of the stone characteristics that influence its use as a building material.…”

“…17,18,19,20 Rock color is strongly influenced by the content, oxidation state and types of iron compounds, as iron is highly absorbent to laser radiation at 1064 nm. In general, color changes are usually attributed to changes in the state of oxidation of iron compounds 13,14,19 . Cooper 1 recommends caution when applying this type of laser to materials, such as sandstone and granite, because of the presence of mica and iron oxide, both highly absorbent to the 1064 nm radiation.…”

Application limits of Q-switched Nd:YAG laser irradiation for stone cleaning based on colour measurements

“…The conditions of application of the laser technique and the optimum laser parameters have been widely studied [1][2][3][4]. When using laser radiation for the cleaning of monumental stones, it is extremely important to determine the threshold fluence that could damage the stone surface.…”

“…The dominant hue is to some extent related to the content, state of oxidation and type of compound of iron (Fe). Fe is a very absorbing and sensitive element to 1064 nm laser radiation and colour changes are usually attributed to changes in the different oxidation states of Fe-rich compounds [3][4][5][6].…”

“…As most of the authors found that the use of a thin water layer enhances the laser-cleaning efficiency [2][3][4], dry and wet stone surfaces were irradiated and colour changes compared.…”