Just as lasers have found countless applications in science, industry, medicine, and entertainment, an array of real and potential uses for lasers in art-conservation analytes and practice have been investigated over the past thirty years. These include holographic recording, holographic recording, holographic nondestructive testing, laser-induced ultrasonic imaging, laser-scattering surface characterization, atomic and molecular analyses, photoacoustic spectroscopy, surface modification, as well as surface divestment and cleaning. The initial endeavors in exploring and assessing the utility of these tools for art conservation are recounted for investigations involving ruby, glass, ion, YAG, carbon dioxide, dye, and excimer lasers as well as high-intensity nonlaser light generators such as xenon flashlamps and argon pinchlamps. Initially, laser divestment/cleaning was, by general consensus, the least plausible laser application in art conservation. In the past ten years it has emerged to dominate all the other applications noted above. Today, at least a dozen firms supply user-friendly laser systems optimized for a range of art-conservation divestment applications. The first-generation laser-cleaning tools are essentially a laser, a beam-delivery device, and a debris- collection accessory. Advanced developmental work has turned in large measure to ancillary subsystems for more sophisticated process control. Of particular importance are acoustic, optical, spectral, EMP, and electronic-vision process control. Beam direction may be via manual, translational-scanner, or robotic beam positioning implemented by means of fiber optics, minors, or prisms and computer control. Substrate thermal alteration and debris redeposition may be minimized or avoided through the incorporation of a gas jet, fluid or fluid jet, or dry-ice blast.

In this paper, modeling of photochemical and photomechanical effects that may be induced during laser assisted cleaning of painted artworks using pulsed UV ablation is presented. The examined laser parameters are the wavelength at 248 nm and 193 nm in the nanosecond regime, and the fluence below and above the ablation threshold. The two polymeric substrate models used are PMMA and blends of PMMA and PS. A test case study is presented.

In this work we investigated for the first time the laser cleaning process of encrusted stones by employing a high power diode laser system. The test have been carried out using a Rofin-Sinar mod. DL025S emitting up to 2.5 kW CW power to clean various samples representing natural encrustation by pollution exposition and graffiti, typically encountered on historical monuments and buildings in urban environment.

In this paper, results are reported on the analysis of a fragment of roman fresco, presumably dated from I century AD. The analysis of the pigments used in the fresco has been performed using the two complementary techniques of micro- LIBS and micro-Raman spectroscopy. Both the techniques allo for microscopic analysis of the samples: however, while micro-Raman spectroscopy gives information on the surface structure of the pigments and binders used, micro-LIBS gives quantitative information on the elemental composition of them, also allowing for stratigraphic analysis with lateral spatial resolution comparable to the micro-Raman technqiue. The joint use of (mu) -LIBS and (mu) -Raman spectroscopy allows for a complete characterization of the sample, and is particularly useful in cases when one of the techniques is not able to give by itself a clear information on the nature of the pigment under study.

Laser cleaning of stones has collected so far the largest number of experiences, employing mainly Nd:YAG laser systems. This class of lasers has been typically used in the two standard emission regimes of Q-switching and Free Running. In our 6 years experience on laser cleaning in conservation, we have studied the interaction process of Nd:YAG laser radiation with various types of stones and surface alterations in order to optimize the laser emission parameters in terms of efficiency and safety of cleaning operations. To this aim we have carried out a critical study on the possible side-effects, which could endanger the result of the cleaning, as well as the future conservation of o artworks. Beside the standard parameters which can be easily adjusted in most of the commercial laser devices, we have considered also the role of the pulse duration, which was varied between the time limits of QS and FR regimes by using laser prototypes suitably develop by us. Such laser systems have been tested in laboratory studies on a large variety of stones and alteration, and are presently applied in the restoration of high valuable statutes and facades of historical buildings. Moreover, the definition of a correct methodology of laser cleaning applications in conservation is presently carried out in cooperation with important public conservation centers of Italy.

In the present work, the effects of nanosecond pulsed laser irradiation on oxidized metallic surfaces were investigated, in order to estimate the possibility of using laser techniques for cleaning applications. After oxidation, the oxide layer developed on the metallic surfaces depends on the composition of the substrate and also on oxidation conditions. In this study a modeling system: pure Fe oxidized at 500 degrees C, has been investigated. The influence of the optical properties of the oxide films on the removal mechanisms and the cleaning efficiency of the laser technique was illustrated by performing specific electrochemical treatments.

In the present work we investigated in a general way the laser cleaning of coated bronzes by Q-switched Nd:YAG lasers. IN particular, the cleaning problems of tinned, slivered and gilded bronzes were theoretically and experimentally analyzed. Besides the laser fluence, the most critical irradiation parameter resulted to be the pulse duration. We demonstrated the advantage to employ specific Q-switching laser sources providing pulse duration in the range of tens of nanoseconds. The optimized laser ablation conditions were successfully experimented in laser cleaning test on original ancient objects.

Selective and precise removal of surface coatings and contaminants can be achieved using lasers with a suitable wavelength. In this study pulsed TEA CO₂- and Nd:YAG- lasers have been used to remove old adhesive and coatings from iron artifacts. This laser cleaning technique can enable extremely precise removal of old coating layers without damaging the underlying metal. Cleaning test on different samples using an Nd:YAG-laser with wavelengths of 1,064 nm, 532 nm and a TEA CO₂-laser with 10,600 nm have been carried out. Trial sample were treated with different kinds of adhesive and coatings used in metal conservation and then cleaned using the three lasers. The results were compared with a conventional technique, micro blasting. Comparison of the laser cleaned surfaces was performed by optical microscopy and Raman-spectroscopy. The comparative study showed that the best results were achieved with the TEA CO₂ laser, with the coatings being removed entirely without damage to the substrate. The original surface of the substrate was preserved and any re-deposited particles could be removed easily using a scalpel or brush after the laser radiation treatment.

This contribution focuses on the interaction of superficial deposits with the marble substrate during the removal by laser radiation. A comparison between cleaning results obtained by the first three harmonic wavelengths of a Q-switched Nd:YAG laser is shown. Experiments were carried out on two sample types. In order to simulate a black encrustation, a model sample was developed based on former studies. In the second case a naturally microbial encrusted marble sample was used. Additionally the temporal ablation development of CaCO3 was investigated by a high speed framing camera. The effects of Nd:YAG laser irradiation at 1064 nm, 532 nm and 355 nm were examined by laser induced breakdown spectroscopy (LIBS), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX) and color measurements using the Commission Internationale de l'Eclairge (CIE) Lab color system with respect to the development and the absolute surface color-change. The results show, that the surface color remaining after the removal of the artificial encrustation by the fundamental wavelength, turned from originally white to yellow. It was possible to identify an Iron content located in nanometer sized spheres on the surface to be the source of the yellowing. The third harmonic wavelength removed the encrustation without a discoloration, whereas the second harmonic was not able to remove the crust appropriately. To remove a superficial biogenic encrustation the 2nd and 3rd harmonic were observed to be the most efficient wavelengths, supporting a good result, which could not be achieved by applying the fundamental wavelength.

Lasers can induce subtle and not so subtle changes in material structure. We have found that certain pigments can undergo chemical and crystallographic changes and concomitant color shifts. Minerals and the related pigments may experience a loss of hydroxyl groups or other chemical reordering. The organic component of skeletal, keratinaceous, and cellulosic materials can be pyrolized, ablated, or etched. Polymers can discolor, undergo structural weakening, or be volatilized. A few of these processes have been investigated with regards to changes on ivory and bone, selected pigments and the removal of dye-based pen ink from porous substrates.

Optimization of restoration techniques employing lasers is dependent on the selection wavelength, cover fluid, pulse duration and method of application. This affects the mechanisms operating during the removal process and hence its efficiency. The risk of unwanted side effects will be more or less controllable depending on the mechanism of removal.

Laser cleaning is an optodynamic process in which the optically induced removal of a liquid or a solid from a substrate is accompanied by a detectable acoustic signal. In our experiments we used both excimer and Q-switched Nd:YAG lasers and we examined both dry and steam laser-cleaning techniques. For the samples we used various metal, glass and marble specimens that were contaminated with particles, rust or a layer of paint. An acoustic wave, produced by the abrupt heating and detachment of the contaminants, was observed with a probe-beam deflection technique. We determined two characteristic parameters: the amplitude and the time-of-flight of the acoustic signal. The decrease of the amplitude and the velocity of propagation, which approaches sonic speed, indicate that the dynamics during the laser-cleaning process progressively weaken. According to this assumption the cleaning process is over when both parameters reach a constant value. If the irradiation with the laser pulses continues, the amplitude begins to rise again and time-of-flight decreases; and this is accompanied by a perceivable surface damage. No amplitude decrease and propagation-time prolongation were observed when the intensity of the incoming laser pulses was above the damage threshold for the particular substrate.

Laser beam transmission through optical fibers is presented in comparison with other techniques for laser cleaning applications. We describe the parameters of importance for a fiber-user and emphasize on the particularities connected to the injection of very high peak power Q-switched lasers into fibers. A description of the last laboratory and commercial developments of cleaning systems with fiber transmission is given, either with single or multiple fibers.

In this lesson, we present an overview on requirements for mobile laser cleaning systems with respect to safety, parameter regimes and performance. The given statements result from investigations over the last four years in developing and testing mobile laser cleaning systems to optimize their technique and to increase the applications. Most of the described features were developed together with restorers in outdoor tests, what gave us a good understanding of the restorers' needs and expectations. Starting with the restorers aim when restoring sculptures or buildings, we describe an ideal system, a complete system and presently used systems. We describe some useful features for mobile cleaning systems and the main aspects of safety philosophy.

The El.En. Group, presently the leading Italian industry in laser technology for biomedical applications, is developing since 1994 a line of laser systems for conservation. The design of such systems has been carried out in the frame of National and International research programs, with the cooperation of research centers working in the fields of laser physics, chemistry and geology, as well as with institutions for conservation that validated laser cleaning techniques in interventions on artworks. The production line dedicated to conservation is composed of solid-state devices emitting in the near and in the mid-IR spectrum, with emission characteristics that have been suitably optimized for various application purposes. In particular, for the treatment of stone surfaces we developed Nd:YAG systems with a suitably tailored pulse duration in the microsecond range, allowing effective and safe operations in the removal of superficial alterations. Two class of lasers are presently commercialized. The 200 class is mainly designed for applications in the conservation yard to clean architectural elements of facades, where the required cleaning productivity must be comparable with the one of micro- sandblasting. The 1000 class, much more compact and lightweight, is suited for applications in the restorer studio on statues.

Fluorescence lidar is a well known instrument that is mainly employed for the remote sensing of the Earth's surface. In recent years, IROE, in collaboration with other Italian and foreign institutions, carried out the first experiments on remote sensing of historical buildings using fluorescence lidar. The main part of these experiments deals with the remote monitoring of biodeteriogens and the lithological characteristics of the building materials. This paper describes the results of the field experiment carried out at the Parma Cathedral and Baptistery in September 2000. Two systems, the tripled Nd:YAG lidar of the Lund Institute of Technology and the XeCl lidar of the CNR-IROE, operated for one week, in order to test the possible applications of both fluorescence point measurement and fluorescence thematic imaging in the remote non-destructive monitoring of buildings. Apart from confirming the possibility of detecting biodeteriogens, for the first time in our knowledge the processing of the fluorescence data made possible the detection of restorations and the distinction between pigments having the same color.

Traditional methods for the removal of unwanted layers from an artwork comprise mechanical or chemical techniques, which often cause (unknown) damage to the object. The Dutch company Art Innovation has developed and realized an innovative laser restoration tool for non-contact cleaning of painted artworks. Accurate beam manipulation techniques in combination with on-line detection equipment make the system suitable for selective cleaning of delicate surfaces.

Paper and parchment cleaning with lasers provides the advantage to be a contact-less and dry process. The absence of chemical agents, its spectroscopic selectivity, micro-precision, computer-aided handling, and the combination with on-line diagnostic techniques makes it attractive for restoration applications. This technique, however, is not only limited by the evaporation of such delicate protein or cellulose fibre structures (i.e. the ablation threshold) or by discolorations, which can be easily detected by the naked eye or by microscopic inspection. Even when the aesthetic appearance is not altered, invisible irreversible chemical modifications may affect the long-term aging behavior negatively. In such cases, only diagnostic tools sensitive for chemical changes can probe the limits of laser cleaning. Deviations of chemical conversion threshold fluences from the well-established ablation threshold fluence values were investigated by multi-spectral imaging techniques at parchment or paper model systems and historical originals. Ultraviolet, visible and infrared reflection, but also visible fluorescence were employed using an imaging system, which operates in a spectral range from 320 nm to 1550 nm. Visible imaging allowed an accurate documentation of the color appearance of the artwork before and after the laser treatment. In-depth information of chemical modifications could be gained by the infrared imaging mode. Surface chemical identification was performed by both diffuse-reflection imaging in the ultraviolet range between 320 and 400 nm, and by visible fluorescence imaging using a 365 nm light source. The results for excimer laser treatment at 308 nm show that not only the laser fluence but also the age of the artefact strongly affects the chemical conversion threshold. Most substrates older than at least several decades exhibited much higher chemical stability than new model systems. This is a strong indication that the aging status of both parchment and paper artefact plays a major role in assessing the laser cleaning limits. That means that the laser processing behavior of model systems can be compared with that of original fibrous artworks to only a very limited extent, and that original artefacts have to be treated rather as individual specimens.

Using a molecular fluorine laser at 157 nm foxing stains were removed successfully from a 16th century old paper. Laser cleaning of stains and foxing from old paper manuscripts is far more effective at 157 nm in comparison to different wavelengths without any yellowish after-effect on the paper. This is because at 157 nm illumination of old paper, compete bond breaking of all the organic molecules of the paper is taking place. Mass spectroscopy at 157 nm and for moderate laser intensities up to 1 mJ/cm² of old paper suffering from foxing and including remains of sticky- tape and stains, indicate organic matter disintegration to small photo fragments atomic, diatomic or triatomic, which are flying apart with supersonic speed. This is because the dissociate excited states of the small organic radicals, occupy the energy region above 6.5 eV.

This paper presents a comparative study of the laser cleaning regimes applied to colored substrates with various chromatic characteristics, including colored paper and printed paper with different dpi (dots per inch) values. Tests are done under microscope with high precision techniques, using controlled Nd:YAG laser. The wavelength preponderantly used in the experiments is the Nd:YAG fundamental regime (1064 nm). Parallel experiments at 532 nm have been developed on difficult cases, or when the results were not satisfactory with 1064 nm. The main part of the work presents some results on stamp cleaning. Experimental results indicate that cleaning efficiency is correlated with the color of substrate, age of the ink on the stamp, color quality and paper quality.

Cuneiform inscriptions has been studied recently using holographically based methods. The goal was to preserve the written information by using the high-resolution and 3D possibilities of holographic recording as well as to investigate the cuneiform inscription signs in the sense of characterizing different types of writing. Here we present the experimental results of the characterization of the cuneiform inscription signs obtained by using an original recognition algorithm and a hybrid device based on liquid crystal displays. Preliminary results which demonstrate the usefulness of both wavelet and matched spatial filtering are given.

During the last years the growing importance of the correct determination of the state of conservation of artworks has been stated by all personalities in care of Cultural Heritage. There exist many analytical methodologies and techniques to individuate the physical and chemical characteristics of artworks, but at present their structural diagnostics mainly rely on the expertise of the restorer and the typical diagnostic process is accomplished mainly through manual and visual inspection of the object surface. The basic idea behind the proposed technique is to substitute human senses with measurement instruments: surfaces are very slightly vibrated by mechanical actuators, while a laser Doppler vibrometer scans the objects measuring surface velocity and producing 2D or 3D maps. Where a defect occurs velocity is higher than neighboring areas so defects can be easily spotted. Laser vibrometers also identify structural resonance frequencies thus leading to a complete characterization of defects. This work will present the most recent results coming out of the application of Scanning Laser Doppler Vibrometers (SLDV) to different types of artworks: mosaics, ceramics, inlaid wood and easel painting. Real artworks and samples realized on purpose have been studied using the proposed technique and different measuring issues resulting from each artwork category will be described.

Laser diagnostic systems based on shearography, vibrometry, and holography principles were employed to investigate the potential implementation of laser techniques in art conservation structural diagnostic field. The employed techniques offered the required measuring variability to allow a first discrimination on complex diagnostic uncertainties encountered often in art conservation. The systems were tested and used to assess the structural condition of well-documented Byzantine icons with known structural problems. Defects and mechanical deformations were identified in various distances from the artworks by alternative employment of techniques. In this way simultaneous eligibility classification of the used systems was also obtained. Results of the on-field application on the XVII century Byzantine icons are herein presented with discussion on the prospects of the techniques in the diagnostic field of art conservation.

In the conservation of historical murals an important issue is the detection of plaster or paint layers that detach from the supporting material and thus threaten to fall off. Commonly, walls are inspected by the acoustic response to a gentle finger-tapping (percussion method). Since this is a costly and cumbersome technique there is need for a metrological instrument serving the same purpose. In the last few years we have shown, that a time-average version of electronic speckle pattern interferometry (ESPI) with increased sensitivity in combination with acoustic excitation of the object can be a powerful tool for monitoring of loose areas. It offers full-field, video real time capability and has the advantage of non-contact and remote operation which, for example, is extremely useful in large buildings. Recently, a fully computer-based evaluation and control system was added to the system to assist in the introduction of the method as a generally approved tool in artwork monitoring. Principles of the method and instrumental features of the equipment are presented and some results and their interpretation obtained with the computerized system in the church and chapel at St. John's convent at Mnstair, Switzerland are demonstrated.

The types of distortions present in audio signals reproduced from Edison phonograph cylinders are considered and classified. An effective approach and algorithm for processing of obtained audio information is proposed. It is shown that the use of a sound signal with frequency range up to 20 KHz at processing has two obvious advantages. The first one allowed to retain the highest harmonics of a sound signal which are not perceived directly by ear, but have a positive influence on the formation of a common sound picture. The second one - in this signal it is more convenient to remove pulse interference (clicks, crackling), since the pulse fronts are steeper and the probability of their detection is increased.

This paper presents trade-off studies of encrustation removing from a relief slab, utilizing a laser emitting four wavelengths from UV to IR. The source of radiation was ReNOVALaser 2 device, generating radiation wavelengths of 1.064 micrometers , 0.532 micrometers , and 0.266 micrometers . The results of investigations are presented on a diagram showing ablation speed as a function of irradiation for four wavelengths.

The great utility of Raman spectroscopy in molecular identification of pigments is well known. Furthermore, the incorporation of fiber optical technology has brought new advantages as compactness, security, weight and price reduction of lasers, and accessibility to analysed object. This is possible thanks to the recent notch and interferential filters, which almost eliminate, respectively, the Rayleigh frequency and both the self Raman spectrum of the fibre and laser plasma frequencies. However, the last has a great dependency on the filter spectral width. In this work, the important role that the quality of the interferential filter plays in the specific case of pigments identification is experimentally shown. Lead yellow pigments (stannate, antimoniate, ternary...) provide very important examples due to the coincidence between a fundamental Raman band of the pigment and some residual plasma frequencies.

Two non-destructive techniques, Raman spectroscopy and particle induced x-ray emission spectrometry, were used for a compete connotation of the Salerno Exultet, an illuminated parchment dated back to 13th century. The Salerno Exultet exhibits several areas which have underdone restoration treatments during the years. The complete connotation of this masterpiece was necessary in order to identify and to distinguish the original and the added pigments. Owing to its dimensions, it has been impossible to analyze the Salerno Exultet directly under the microscope of our Micro- Raman spectrometer. We have therefore used optical fibers connected to a three axis micro-positioned measurement head mounted on a large metal frame. PIXE analysis was performed using the portable instrumentation set up by the INFN-LANDIS Laboratory, Catania, Italy. The combination of these two complementary techniques allowed us to reveal a palette formed by lapis-lazuli, cinnabar, verdigris, earths organic lakes and chalk.

We report on a Raman study performed on sub-millimetric sized samples taken from the surface of a fresco painted in 1522-24 by Parmigianino (Girolamo Francesco Maria Mazzola, 1503-1540) in the second Chapel of the S. Giovanni Evangelista Church in Parma, Italy, whose restoration has been recently fully completed. The 'palette' of pigments used by the artist has been established. X-ray micro-fluorescence measurements confirm the results obtained by the micro-Raman technique.

Scientific investigation methods are founding their place besides the stylistic-historical study methods in art research works. In particular, optical techniques, transferred from other fields or developed ad hoc, can make a strong contribution to the safeguarding and exploitation of cultural heritage. This paper describes the use of different optical techniques, such as holographic interferometry, decorrelation, shearography and ESPI, in the diagnostics of works of art. A comparison between different methods is obtained by performing tests on specially designed models, prepared using typical techniques and materials. Inside the model structure, a number of defects of known types, form and extension are inserted. The different features of each technique are outlined and a comparison with IR thermography is also carried out.

At the beginning, the ranges of laser-matter interaction in dependence eon the radiation power density are shortly discussed. Next, the suitable hydrodynamic model is described and some results of numerical calculations of interaction phenomena are presented. Finally, the measurements of amplitude of elastic wave generated inside object by interaction with pulse, Nd:YAG, Q-switched laser radiation are proposed. Measurements are conducted using Michelson interferometer.