Colour changes of a historical Gotland sandstone caused by laser surface cleaning in ambient air and N2 flow

Laser surface cleaning of stones and some metal objects

“…The figure also shows crosssectional views of decreased crust after laser illumination. The use of ambient oxygen permitted very good cleaning and better than other gases, due to its smaller ionization energy (12.1 eV) and higher thermal conductivity (63.64cal/sec.cm.c o x10 6 [16]. Part of the laser beam energy was used to burn the oxygen in an exothermal reaction Which increased the thermal energy at the surface.…”

“…Laser cleaning is based on selective sputtering of optically absorbing pollutants; first adopted by repairs project in 1993 at the Cathedral of Amiens [10][11][12]. It is effective, controllable, environmentally friendly and flexible; more than conventional techniques [13][14][15][16][17]. High peak power pulsed lasers are utilized to remove surface stains and weathering effects from sculptures, coins, marble, granite, frescos, paintings, paper and textiles [8,18].…”

“…In 2006, L. Bartoli, et al [22] showed that short laser pulses are more effective than long duration ones in the cleaning of real and simulated crusts from marble. In the same year, M. Jasi et al [16] used 0.5 J/cm 2 fluence pulsed Nd: YAG laser operating at 1064nm to completely remove 100-200 μm thick porous encrustation after 12-18 laser pulses. In 2013, S. Pozoa, et al [26] investigated the removal of sulphate-rich black crusts on granite using 6-10 ns, 10 Hz, Nd: YAG laser; operating at 266 nm, 355 nm, 532 nm harmonics and fundamental 1064 nm wavelengths.…”