Lasers Cleaning of Patrimonial Plasters

Abstract

International audienceThe use of the lasers Q-switched Nd:YAG to remove the dust of the stone monuments especially sculpture gradually replaces the more abrasive technique of sandblasting. This tendency made us consider the lasers as solution for the cleaning of ceramics and the plasters. Indeed in museums, these materials are often covered with dirty mark (dust, grease, etc.) which is difficult to remove without damaging the object. This paper deals with the impact of different types of lasers (Nd:YAG first and third harmonic) irradiation on plaster and with the effects on its morphology and its crystallography. Plaster is an interesting material because of its typical acicular crystals altered at low temperature. That is why synthesis samples were prepared, constrained in temperature then analysed by various processes (SEM, XRD, TGA. . . ). These results were compared with samples cleaned by laser. That enabled us to conclude that plasters cleaned by UV-laser (third harmonic of the Nd:YAG) underwent neither yellowing, nor morphological or crystallographic changes. It has to be opposed to the intense yellowing, and sometimes morphological destruction, which appears with an infrared wavelength (first harmonic of the Nd:YAG)

The two-wavelength laser cleaning methodology; theoretical background and examples from its application on CH objects and monuments with emphasis to the Athens Acropolis sculptures

“…This is a rather composite problem as this crust may have soiling particles (internal dust), organic materials (from casting processes), as well as biological organisms. Given the sensitivity of gypsum [38][39], as well as its solubility to water, cleaning interventions on such objects are particularly demanding.…”

Investigating the Potential of the Er:YAG Laser for the Removal of Cemented Dust from Limestone and Painted Plaster

“…The Nd:YAG laser, emitting at 1064 nm and its harmonics, has demonstrated to be the most employed system for the cleaning of a different range of materials [11,12]. It has been extensively applied for the removal of black crusts of various thickness and biological growth from stone, marble and plaster [13][14][15][16][17][18], as part of the laser energy is selectively absorbed by dark materials and reflected by the underneath substrate. This makes the laser cleaning process self-limiting and ideal for such treatment.…”