Catálogo de publicaciones - libros

In the present work, the feasibility of sulphur detection was demonstrated during laser ablation of the gypsum layers on the polluted surface of aged marbles. The laser used for cleaning and generation of the LIBS signal was a Q-Switched Nd:YAG emitting dual pulses at 1,064 nm. Different sulphur emission lines were identified through comparative LIBS measurements on gypsum encrustation and K2SO4 and MgSO4 reference materials, but only few, not weak, sulphur lines resulted suitable for monitoring the cleaning of marble, due to the overlap of most features with emissions from bulk marble constituents. Sulphur vertical distribution in the encrustation was then monitored by LIBS during the cleaning. Results of LIBS sulphur stratigraphy were comparable with those obtained by SEM–EDX measurements. In the present study it was possible to establish by LIBS the boundary between bulk marble and its encrustation containing gypsum and, consequently, to determine the optimal point for the interruption of the laser cleaning at the end of the heavily sulphated crust.

Based on a commercial miniature spectrometer, we have built a LIBSsystem for online monitoring and controlling during laser cleaning of artworks. In contrast to common LIBS set-ups with ICCDs, our system offers less sensitivity and λ-resolution. This system is unsuitable for high resolution elemental identification but it is applicable for the detection of “spectral fingerprints”. A powerful method of comparison online spectra during laser cleaning process with reference spectra is the analysis of correlation. Based on “Pearson’s correlation”, the linear relationship between entire data sets of both spectra are classified by the correlation coefficient r . In practise of laser cleaning a permanent comparison of the spectrum from the ablated layer with a reference spectrum of the layer to be preserved is necessary. Thus, online monitoring of the cleaning process is enabled by permanent estimation of r . In case of closed-loop laser cleaning the ablation will continue until r exceeds a predefined value and subsequently the ablation process is automatically stopped.

The recent incorporation of laser devices provides advanced tools for assisting the conservation and restoration of Cultural Heritage. It is necessary to have as complete as possible understanding of the object state before evaluating or defining the reach of the restoration process. Thus, a special effort is devoted to surveying, measuring and generating a high-resolution 3D model prior to restoration planning. This work presents results of several experiments performed on damaged pieces for evaluation purposes in Cultural Heritage. Some software tools are applied for carving-work analysis, conservation-state monitoring, and simulation of weathering processes for evaluating temporal changes. In all cases considered, a high resolution information capture has been performed with a laser scanner, the Minolta 910. Our approach is flexible enough to be adapted to other kinds of pieces or Cultural Heritage artefacts, in order to provide an assessment for intervention planning in conservation and restoration tasks.

The Raman and laser-induced breakdown spectroscopy (LIBS) techniques were applied for the pigment identification in polychrome layers on a fourteenth/fifteenth century wooden crucifix. In the Raman spectra, characteristic bands associated with compounds of the pigment samples taken from different areas of the object are observed. Groups of bands corresponding to the original white, red, and green pigments allow the identification of chalk, vermilion, red lead, malachite, and azurite. From the presence of bands ascribed to Prussian blue (282, 538 cm ? 1) and chrome yellow (338, 360, 403 cm ? 1) known since eighteenth century, retouching of some statue parts can be concluded. The elemental composition is obtained from LIBS profiles recorded under excitation at 248 and 266 nm. The gold-leaf technique is identified and the presence of Cu, Pb, Cr, Fe, CN, C2, and Ca agrees with the pigment composition applied for re-touching and observed in the Raman bands.

A study on the painting materials (pigments and binders) of the famous painting “Madonna col Bambino e S. Giovannino” by Sandro Botticelli, located in the Museo Civico of Piacenza (Italy), was performed before a recent restoration. The painting materials were investigated by the analysis of five millimetric samples taken in damaged regions. The pigments were determined using the micro-Raman spectroscopy, with the 632.8nm line of a He–Ne laser. Despite the strong fluorescence background, the nature of the ground layer (gypsum and anhydrite) and of most pigments (i.e. goethite, lapis lazuli, white lead) was determined. Gas chromatography coupled with mass spectroscopy (GC/MS) was used to determine the organic binder media, and in particular proteinaceous and lipid materials. Egg and animal glue were found, while no siccative oils were detected.

The main constituents of textiles, paper and parchment are proteins and polysaccharides. These organic matters are particularly sensitive to damage such as spotting, dimensional deformations, depolymerisation, and offer a surface particularly suitable towards the deposition of various materials. In the case of the paper and parchment cleaning, traditional techniques are well known, as well as the risk to make halos and shades when using the mechanical action of a scalpel or solvent mixtures to thin the spots. For textile artefacts the need to remove dust, spots, and mud residues is a duty though this action is quite difficult with traditional methods because the dense weft and warp structure does not allow a complete cleaning, without a minor damage of the artwork. The authors set up a research program to verify the possibility and the results of an Er:YAG laser equipment, emitting at 2,940 nm, following the results achieved previously in OPD on the treatment of organic materials (LACONA IV proceedings).

Conservation often requires the removal of oxide layers from metal artifacts and new cleaning methods are being developed all the time. This paper provides a quantitative comparison of eight cleaning methods, three of which are mechanical (brushing or micro-blasting with Al2O3 or glass beads) and five of which are laser dependent (TEA CO2 or Nd:YAG laser, with or without surface water). Surface profilometry and scanning electron microscopy have been used to compare the cleaned surfaces with the original, known, surface geometries.

Nanosecond laser (532 nm) cleaning of soiled silk (naturally aged and new fabrics) is discussed in terms of an adequate choice of the processing parameters laser fluence and pulse number to achieve a satisfying cleaning effect and to avoid damage of the sensitive textiles. Experimental limits will be presented and compared to theoretical considerations utilizing graphite as a model for the soil.

While in storage and on exhibition, baskets can accumulate dirt that is aesthetically undesirable and even harmful. The nature of the woven structure, as well as the porosity of organic materials, causes difficulty in the removal of accumulated dirt. This chapter presents results from a study of basket-cleaning methods focusing on how Nd:YAG laser-cleaned samples are compare with those cleaned by more commonly used methods. Cleaning tests were performed on stem, bark, and root sample materials in order to examine the effects of cleaning on a variety of plant materials that are commonly encountered with basketry. Photography, optical microscopy, and scanning electron microscopy were used to document and compare the effectiveness and drawbacks of these methods. The results indicated that plant materials with protective cuticle layers can be effectively cleaned using lowtech methods and such fibers would not greatly benefit from laser cleaning. Materials without protective cuticle layers are more sensitive to mechanical cleaning and could possibly be more safely cleaned using lasers.

This chapter focuses on the use of Er:YAG laser cleaning technique for the removal of unwanted and/or degraded materials both from a large series of reference standards (overpainting, varnishes, patinas, and restoration materials) which simulate the layering of old paintings, and also examples from old paintings. A series of diagnostic controls (optical microscopy, SEM, FT-IR, GC–MS, and topographic techniques) were designed to study the effects of the laser radiation on the surface components, including morphological, optical, and chemical examination. The most significant results show that an effective thin-layer-removal of about 90% is obtained by submitting the painted surfaces to the laser exposure, while the rest of cleaning is rapidly accomplished in safety by applying mild solvents or aqueous methods. Consequently, possible interference with the original substrate can be noticeably minimized. No degradation compound induced by laser energy was formed. The laser cleaning procedure applied on an oil painting canvas “Morte di Adone” (seventeenth century), and on a panel tempera painting “San Nicola e San Giusto” of Domenico di Michelino (fifteenth century) shows that the surfaces cleaned by this system exhibit a morphology quite similar to that obtained by traditional cleaning methods.