Changes of the elemental composition due to laser surface cleaning of a naturally crusted historical sandstone were investigated by means of the SEM/EDX technique. Data obtained for stone samples prior to and after laser irradiation were compared with those for noncrusted, reference ones. It has been observed that the crust removal resulting from ablative cleaning was accompanied by a decrease of the partial content of elements Al, S, K, Ca, and Mg in the range of 60&#8211;80<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math> of their initial value recorded for the noncleaned, crust-covered stone surface. In the stone layer just under the crust coverage, a structure characterized by intergranular spaces between the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>SiO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> grains being the main sandstone component filled with degraded binder was observed. From the coincidence of the binder destruction and chemical composition of the crust, the stone surface destruction due to the long-term interaction of environmental pollution was deduced. The spatial distributions of individual elements
obtained by mapping after laser irradiation indicated that besides <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>SiO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> the content of elemental components in the sandstone surface layer decreased by 50<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math>, whereas for Fe with the initial content of 4<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math> and other surface remnants: P, Ti, Zn, and Cl&#x2014;all below 1<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math>, insignificant changes were only revealed. It was concluded in agreement with the literature that surface cleaning by means of the 1064 nm laser does not cause removal of iron from the sandstone surface.

Marta  Jasi&#324;ska

J&#248;rn  Bredal-J&#248;rgensen

Gerard  &#346;liwi&#324;ski

Observation of the Laser Cleaning Effect on the Gotland Sandstone Elemental Composition

Remote laser-induced fluorescence of stone materials was performed with application towards cultural heritage. Fluorescence was induced in targets <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>&#x223C;</mml:mo><mml:mn>60</mml:mn></mml:mrow></mml:math> m from a mobile lidar laboratory by ultraviolet laser light, either from a frequency-tripled Nd:YAG laser or from an optical parametric oscillator system. Analysis was performed on combined spectra from the different excitation wavelengths and it was noted that important additional information can be gained when using several excitation wavelengths.

Rasmus  Gr&#246;nlund

Jenny  H&#228;llstr&#246;m

Ann  Johansson

Kerstin  Barup

Sune  Svanberg

Remote Multicolor Excitation Laser-Induced Fluorescence Imaging

Laser-induced fluorescence (LIF) spectroscopy can provide nondestructive, qualitative analysis of protein-based binding media found in artworks. Fluorescence emissions from proteins in egg yolk and egg white are due to autofluorescent aromatic amino acids as well as other native and age-related fluorophores, but the potential of fluorescence spectroscopy for the differentiation between binding media is dependent on the choice of a suitable excitation wavelength and limited by problems in interpretation. However, a better understanding of emission spectra associated with LIF can be achieved following comparisons with total emission fluorescence spectra where a series of consecutive emission spectra are recorded over a specific range. Results using nanosecond UV laser sources for LIF of egg-based binding media are presented which are rationalised following comparisons with total emission spectra. Specifically, fluorescence is assigned to tryptophan and oxidation products of amino acids; in the case of egg yolk, fatty-acid polymerisation and age-related degradation products account for the formation of fluorophores.

Austin  Nevin

Demetrios  Anglos

Assisted Interpretation of Laser-Induced Fluorescence Spectra of Egg-Based Binding Media Using Total Emission Fluorescence Spectroscopy

Nanosecond laser (1064 nm wavelength) cleaning of artificially soiled paper as a model sample simulating a real-world artwork was performed. During the cleaning process, the ejection of particles was monitored in situ by means of a dust monitor (8 size classes, ranging from 0.3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x03BC;</mml:mi></mml:math>m to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>&#x003E;</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math>&#160;<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x03BC;</mml:mi></mml:math>m) and ex situ using a mini-cascade impactor (MKI, 5 stages). The cleaning
result was analyzed by scanning electron microscopy (SEM) considering possible laser-induced damages to the substrate. Size distributions of emitted particles were measured depending on the processing parameters: laser fluence, 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>F</mml:mi></mml:math>, and pulse number per spot, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>N</mml:mi></mml:math>. High numbers of large (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>&#x003E;</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math>&#160;<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x03BC;</mml:mi></mml:math>m) particles were collected by the mini-cascade impactor indicating 
a gas dynamical liftoff process. Obviously, these particles were not affected by the laser-matter interaction. The different methods (SEM, MKI, and dust monitor) are compared with respect to their usefulness for a proper interpretation of the cleaning results.

Roland  Wurster

Simone  Pentzien

Andrea  Conradi

J&#246;rg  Kr&#252;ger

Characterization of Laser-Generated Microparticles by Means of a Dust Monitor and SEM Imaging

Laser cleaning tests were performed on five archaeological copper alloy objects using a Q-switched Nd:YAG laser at 1064 nm. As a comparison, a section of each object was cleaned mechanically. Prior to cleaning, cross-sections were prepared to characterise the corrosion crust and help to locate the position of the original surface. Laser cleaning was not successful at removing burial deposits on two of the objects. For the other three objects, the laser removed most of the corrosion crust. This was not always satisfactory, as cleaning was sometimes accompanied by the loss of the original surface. In addition, laser-cleaned surfaces were matt compared to mechanically cleaned surfaces. In some instances, the former had a disfiguring purple hue which was attributed to the formation of particles that could be seen when examining the surface using scanning electron microscopy. For all the objects examined here, superior results were obtained by mechanical cleaning.

Capucine  Korenberg

Alexandra  Baldwin

Laser Cleaning Tests on Archaeological Copper Alloys Using an ND:YAG Laser

We present results from preliminary laser cleaning studies performed on a 20th century modern painting, in which laser-induced breakdown spectroscopy (LIBS) was employed for monitoring the progress of material removal. This synergistic approach, that combines laser ablation cleaning with spectroscopic control, is of obvious importance as it offers a reliable means of ensuring proper conservation and could be the basis of a standard
protocol for laser-based restoration procedures.

K.  Melessanaki

C.  Stringari

C.  Fotakis

D.  Anglos

Laser Cleaning and Spectroscopy: A Synergistic Approach in the Conservation of a Modern Painting

This work offers an automatic identification system of Raman spectra of artistic pigments.  The proposed methodology is based on a fuzzy logic system, and uses principal component analysis to reduce redundancies in data and the correlation operator as an index of similarity between two Raman spectra. Moreover, as sometimes pigments are used in mixtures by artist, the designed system is able to recognize binary mixtures of pigments on the basis of their Raman fingerprints.

M.  Castanys

M. J. Soneira

R.  Perez-Pueyo

Automatic Identification of Artistic Pigments by Raman
 Spectroscopy Using Fuzzy Logic and Principal Component Analysis

In the field of cultural heritage, the study of the materials used by the artist is useful both for the knowledge of the artwork and for conservation and restoring interventions. In this communication, we present results of some decorations analysis obtained by the use of two complementary laser techniques: micro-LIBS and micro-Raman spectroscopy. With both techniques it is possible to operate in a practically nondestructive way on the artwork itself, without sampling or pretreatment. Micro-Raman spectroscopy gives information on the molecular structure of the pigments used, while micro-LIBS can give quantitative information about the elemental composition of the same materials. In this paper, qualitative results are reported obtained on the study of some Neolithic potteries coming from the archaeological site of Trasano (Matera); the fragments show decorations in different colors, red, black, and white. The aim of the study was detecting whether the colored decorations were made by using added pigments or came from the manufacturing process.

Lucia  Angeli

Claudio  Arias

Gabriele  Cristoforetti

Cristina  Fabbri

Stefano  Legnaioli

Vincenzo  Palleschi

Giovanna  Radi

Azenio  Salvetti

Elisabetta  Tognoni

Spectroscopic Techniques Applied to the Study of Italian Painted Neolithic Potteries

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Laser Chemistry

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