Practical issues in laser cleaning of stone and painted artefacts: optimisation procedures and side effects

Pouli, Paraskevi; Oujja, M.; Castillejo, Marta

doi:10.1007/s00339-011-6696-2

Cited by 89 publications

(56 citation statements)

References 76 publications

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“…Discoloration issues have been extensively and long studied and a number of publications have been focused on their understanding [3,[17][18][19], while emphasis has been also given to the development of eliminative and remedial approaches on the basis of careful choice and fine-tuning of the operative laser parameters (such as the laser wavelength [11,18,[21][22][23] and pulse duration [17,24].…”

Section: The Two-wavelength Cleaning Methodology; Background Informatmentioning

confidence: 99%

“…As a result the energy density (fluence, F) threshold value for encrustation removal is significant lower than the one for substrate/marble damage and thus selective and self-limiting cleaning is feasible. Typical F threshold values determined for 1064 nm ablation of black pollution crust and Pentelic marble are 0.8 and 3.5 J/cm 2 , respectively [18]. Nevertheless, the use of IR laser beams both on technical samples simulating pollution encrustation, as well as on real marble fragments with pollution crusts, often resulted in surfaces discoloured to yellow-brown.…”

Section: The Two-wavelength Cleaning Methodology; Background Informatmentioning

confidence: 99%

“…3 illustrate the superiority of the two-wavelength laser cleaning methodology as regards the final colour, surface morphology and homogeneity of the cleaned areas, while indicating the limitations of the individual IR and UV cleaning regimes, as well as of their SQ use. The methodology has been thoroughly tested through a series of studies, both on technical samples and real fragments [18,30,31], in order to determine the optimal conditions for its application. These results have allowed its adaptation and fine-tuning for the cleaning challenges of the Athens Acropolis Sculptures and Monuments with success.…”

Section: The Two-wavelength Cleaning Methodology; Background Informatmentioning

confidence: 99%

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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

et al. 2016

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The two-wavelength laser cleaning methodology has been introduced and developed in order to meet demanding cleaning challenges in CH. The innovation lies on the combined use of two laser beams, allowing thus control of the laser ablation effective regimes towards an efficient and safe cleaning result. A series of studies on technical samples and real fragments aimed at defining and refining this methodology in order to ensure that the original surface, including its details and historic traces, will be safeguarded. In this paper related research and applications will be presented in an attempt to enlighten the associated laser ablation processes, as well as the potential cleaning applications in CH field. Laser-assisted removal of pollution accumulations from the Athens Acropolis monuments and sculptures is a unique highlight on the use of this methodology in practice. IESL-FORTH in collaboration with the Acropolis Restoration Service and the Acropolis Museum has developed an innovative cleaning methodology and a prototype laser cleaning system, which since 2002 have been introduced to the everyday conservation practice and will be presented in this paper.

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Section: The Two-wavelength Cleaning Methodology; Background Informatmentioning

confidence: 99%

Section: The Two-wavelength Cleaning Methodology; Background Informatmentioning

confidence: 99%

Section: The Two-wavelength Cleaning Methodology; Background Informatmentioning

confidence: 99%

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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

et al. 2016

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“…Their presence is related to well-preserved authentic surfaces with sharp reliefs, as in the case of Parthenon 'epidermis' and sculptural details (i.e. traces of ancient tooling) (Galanos and Doganis, 2003), and therefore they must be preserved (Pouli et al, 2012).…”

Section: The Cleaning Challengementioning

confidence: 99%

Laser-assisted removal of dark cement crusts from mineral gypsum (selenite) architectural elements of peripheral monuments at Knossos

Grammatikakis¹,

Demadis

Melessanaki

et al. 2015

Studies in Conservation

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The aim of this study was the efficient removal of dark cement crusts from selenite (mineral gypsum) surfaces using lasers. The conservation challenge is to remove a hard, insoluble, and often significantly thick encrustation without affecting the particularly sensitive mineral substrate gypsum, which is susceptible to chemical transformation. Preliminary studies were focused on the determination of removal thresholds for the cement bulk and the establishment of efficient laser cleaning operative parameters. Concurrently, analytical investigations were focused on the irradiated surfaces in order to ensure that the recommended laser operating parameters would safeguard the surface, colour, and composition of gypsum. Analytical techniques (Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy with energydispersive X-ray analysis) were used to verify that no discolouration or chemical alteration occurred to the fragile gypsum substrate due to the dehydration of pristine gypsum (to hemihydrate and anhydrous calcium sulphate). The results of this study as well as its application are presented and discussed with emphasis on the surface integrity of the exposed fragile selenite substrates.

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“…The laser-cleaned objects have generally a darker and sometimes a more yellow appearance. A significant number of investigations have been performed to date on the topic [1]: it is now admitted that the phenomenon may be linked to several causes, among others an unveiling of strongly colored surfaces hidden by black surface layers [2]. Another hypothesis raised in the 2000's links the specific color to the presence of nanometer-size particles [3].…”

Section: Introductionmentioning

confidence: 99%

Laser yellowing effect: study of the nanophases created by laser irradiation of synthetic black crusts using transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) spectroscopy

Godet¹,

Vergès‐Belmin²,

Saheb³

et al. 2017

Proceedings of the International Conference LACONA XI

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Nd:YAG Q-Switched laser cleaning at 1064 nm can sometimes lead to a more yellow appearance of the stone surface in comparison with other cleaning techniques. The yellow hue can originate from different contributions among which the presence of nano-sized residues generated by the laser interaction with the surface materials to be eliminated. In this study, the nature of such residues has been investigated. The analyzed materials are (i) particles collected from a pure gypsum reference plate; (ii) a synthetic crust, composed of 80 wt % natural black crust and 20 wt % synthetic gypsum; (iii) particles ejected from the synthetic crust during laser irradiation. Optical, scanning electron and transmission electron microscopies were used to link color changes at the macro-scale to morphology changes at the submicron-and nano-scales. Chemical composition was also obtained at the nano-scale using TEM coupled with energy dispersive X-ray (EDX) spectroscopy. This multi-scale approach was combined with electron paramagnetic resonance spectroscopy (EPR) analysis at low and room temperatures to examine the possible presence of iron-containing species presenting particular magnetic properties in the sample before and after irradiation. Under laser irradiation, both the crust sample and the ejected gypsum particles take a yellow color. This color shift can be linked with morphology changes occurring at the nano-scale: gypsum crystals from the reference plate show a smooth surface, while those coming from the synthetic black crust are, after irradiation, covered by many spherical nanoparticles and a rough nano-layer ranging from less than 20 nm to more than 100 64Marie Godet et al.nm. TEM-EDX analysis reveals that the two types of nanostructures have a chemical composition very similar to that of iron-rich coal fly-ashes called magnetospheres or ferrospheres. It is suggested that laser irradiation induces a transformation of micrometric size fly-ashes present in the black crust into different types of nanostructures having a chemical composition similar to the one of ferrospheres. EPR analysis demonstrates the presence of ferri-ferro-superparamagnetic species both before and after irradiation, thus indicating that nanosized magnetic iron compounds probably corresponding to magnetite or maghemite oxides are present in the black crust, most probably crystallized on the surface or within the fly-ashes microparticles. This study brings to light the contribution of fly-ashes to the laser induced yellowing process.

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Practical issues in laser cleaning of stone and painted artefacts: optimisation procedures and side effects

Cited by 89 publications

References 76 publications

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

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

Laser-assisted removal of dark cement crusts from mineral gypsum (selenite) architectural elements of peripheral monuments at Knossos

Laser yellowing effect: study of the nanophases created by laser irradiation of synthetic black crusts using transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) spectroscopy

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