Role of marble microstructure in near-infrared laser-induced damage during laser cleaning

Abstract

When marble is cleaned by nanosecond neodymium yttrium-aluminum-garnet lasers ͑1064 nm͒, strongly absorbing surface contaminants are removed at fluences substantially below the damage threshold for the much less absorptive marble substrate. Recent studies have shown, however, that unacceptable roughening of the marble surface also may occur at low fluences due to removal of individual grains. In order to elucidate this effect, we have compared the low-fluence response of marbles with two different grain sizes and single-crystal calcite, in the fluence range 0.12-1.25 J cm Ϫ2 . Damage was greater in fine-grained than coarse-grained marble, and did not occur in the single-crystal calcite at these fluences. The temperature rise following defect-mediated absorption triggers thermal plasma emission and generates shock waves; the concomitant surface damage depends on the size and crystallographic orientation of the crystals. Laser irradiation anneals the defects and increases ''crystallite size.'' The implications for the laser-assisted cleaning of marble artworks are outlined.

Color changes in architectural limestones from pollution and cleaning

“…It probably arises from thermal reactions in iron-rich minerals that give this dramatic change in color. Other authors 13 have found mechanical damage and roughening of marble surfaces at irradiative fluences lower than that used in this research. Laser clean can also increase surface roughness, but the expected changes would be towards lighter and more saturated tones.…”

“…Chromatic modifications in laser-treated dry-stone surfaces are usually attributed to changes in the oxidation state of iron compounds. 11 Moreover, laser cleaning could also result in variations in surface roughness 13 that could alter stone color. 2 The damage thresholds for stone also depend on the physical state of the stone surface (e.g.…”

Template-Assisted Crystallization of Sulfates onto Calcite: Implications for the Prevention of Salt Damage

“…Thus, the effective stresses are 4.23 and 1.68 MPa in the case of mirabilite crystallization in the absence and in the presence of DTPMP. The tensile strength of the tested limestone is 1.8 ± 0.5 MPa . Salt damage occurs when the effective stress due to generation of salt crystallization pressure in a porous material is higher than the tensile stress. , It follows that the reduction in crystallization pressure associated with the presence of DTPMP explains the reduction in damage to the porous stone support observed in our macroscale salt crystallization tests.…”

Laser removal of graffiti from Pink Morelia Quarry

“…Acc.V Spot Magri Det WD 10.0 kV 4.0 500x SE 11.6 CACTI 50 tan The success of this method lies in its relatively low irradiance. This reduces the heating of the stone surface, and, at the same time, the sample cools down between both laser passes.…”