Laser Cleaning Tests Research Articles

The Surface Properties of an Aviation Aluminum Alloy after Laser Cleaning

In this study, we explored the effects of a laser cleaning process on the surface properties of an aerospace aluminum alloy. We performed surface cleaning on an AA2024 aluminum alloy. Through SEM and EDS analyses on the surface of the aluminum alloy samples after cleaning, the cleaning effect on the aluminum alloy under different laser energy densities was studied. After laser cleaning, residual stress, hardness, friction, and wear tests were performed on the aluminum alloy samples. The experimental results demonstrated that the oxides on the surface of AA2024 could be effectively removed when the laser energy density was 10.5 J/cm2. With an increase in the laser energy density, the friction and wear properties of the AA2024 surface could be improved. Laser cleaning could also generate a new hardened layer and residual tensile stress on the surface of AA2024. This article provides a reference for applying laser cleaning in the aerospace field by studying the structure and mechanical properties of an aluminum alloy after laser cleaning.

An analytical evaluation of Er:YAG laser cleaning tests on a nineteenth century varnished painting

This paper aims to evaluate the Er:YAG laser efficacy to safely thin a varnish on a modern 19th century oil painting. Tests were carried out under single and multiple laser scans directly on the surface (dry) or after pre-wetting with deionised water (DIW) and a non-ionic surfactant (Tween 20), fluence ranges of 0.56–2.40 J/cm2 and 100 μsec pulse duration. Microscope glass coverslips were placed on the painting surface during irradiation to collect the condensed resin fragments that were extracted from the varnished surfaces. Spectral clusterisation maps of Multispectral Imaging (MSI) data of the irradiated surface supported the evaluation of the procedure. Further evaluation was performed by stereomicroscopy and colourimetry. Fourier Transform Infrared spectroscopy (FT-IR) and Pyrolysis Gas Chromatography / Mass Spectrometry (Py-GC/MS) analysis indicated that the varnish resin was dammar. The collected resin fragments were analysed by FT-IR. The results showed that the resin did not degrade even at the highest level of fluence employed, thereby allowing a subsequent analytical evaluation.

Nanomaterials for Conservation of Artistic Stones: Performance and Removal Tests by Laser Cleaning

In this work, nanomaterials were used as consolidants and protective layers for artistic stones. Synthetized nanocomposites were applied on marble and their performances as protective and water repellent coating were characterized. For the preparation of the novel nanocomposites, SiO2 and TiO2 nanoparticles were synthesized by laser pyrolysis and were dispersed in acrylic polymer and silicon-based resin. To evaluate the retreatability of water repellent treatments, the capability of laser to remove protective layers was explored. Laser cleaning tests with different working parameters have been carried out to optimize the effectiveness of the process. The effects of laser treatments on stone surfaces and on the applied nanocomposites were estimated by using confocal optical microscopy and Laser-Induced Fluorescence (LIF).

An integrated approach to the conservation of a wooden sculpture representing Saint Joseph by the workshop of Ignaz Günther (1727–1775): Analysis, laser cleaning and 3D documentation

Abstract This paper reports the conservation procedure applied to a wooden sculpture representing Saint Joseph attributed to the workshop of Ignaz Gunther (1727–1775). The component material of the wooden sculpture was identified by observing the thin sections under an optical microscope; the materials layered on the surface were analyzed by optical microscopy, micro-Raman and Fourier transform infrared spectroscopy. The laser cleaning tests were carried out with a Q-switched Nd:YAG system. The surface was examined before and after the cleaning with the aid of a video-microscope, reflectance spectrophotometer and scanning electron microscopy. The steps of the work were documented on a digital tri-dimensional model of the sculpture created by a close range image system in order to carefully register scientific, technical, conservative, and material aspects. The microscopic observation of wood thin sections allows identifying it as lime tree. The analysis of the surface materials highlighted the presence of lead white applied by a siccative oil and barium sulphate. The infrared spectroscopic analysis of the brown surface layer revealed the presence of shellac. The laser cleaning proved an effective method to remove the surface dirt and to reduce the aged protective layer without affecting negatively the wood. The diagnostic analysis carried out prior and during the cleaning process was fundamental to verify the applicability of the laser to the wood surface in order to obtain an efficient cleaning action without secondary damaging effects. In addition, considering the reduced number of laser cleaning examples applied to wooden material available in literature, the documentation of the adopted working process could be a useful reference for the divulgation and sharing of the obtained data.

Investigation into the removal of graffiti on mineral supports: Comparison of nano-second Nd:YAG laser cleaning with traditional mechanical and chemical methods

This contribution discusses the analysis of polymeric paint layers and the removal of graffiti from historical buildings and sculptures. The main objective of the research is to compare the effectiveness of nano-second (ns) laser ablation with traditional cleaning procedures for the removal of painted graffiti from the surface of monuments. The vast number of various aerosol paints used for graffiti which contain different binders, solvents, and pigments does not allow the use of a single or universal cleaning method. In this study the efficacy of laser ablation was compared with chemical and mechanical cleaning methods. The laser system used for cleaning was a ns Nd:YAG, irradiating at 1064, 532, and 355 nm. Laser cleaning tests were performed on samples of limestone, sandstone, plaster, and brick covered with black, white, and red graffiti paints based on nitrocellulose, acrylic, and alkyd resins. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) were used to characterize paint binders. The morphology of treated surfaces was examined by optical microscopy and SEM. The results indicated the high efficiency of laser cleaning compared to traditional graffiti removal methods. A strong dependence of the efficacy of laser ablation on the paint composition and the porosity of the substrate was observed.

Laser cleaning of a nineteenth-century bronze sculpture: In situ multi-analytical evaluation

Laser cleaning of bronze artefacts is a very promising conservation approach and its wider distribution would benefit from further studies of its advantages and drawbacks. Some important references are available, yet laser cleaning cannot be considered a traditional method for bronze surfaces. In this paper, we report on the evaluation of cleaning tests performed on an important statue of Napoleon, depicted as Mars the Peacemaker, cast by Righetti in 1811 after a model by Antonio Canova. The sculpture is exposed to the outdoor environment in the main courtyard of the Brera Gallery, Milan, Italy. An analytical survey of corrosion products was carried out using X-ray diffraction, micro-Fourier transform infrared spectroscopy (μFTIR), and μRaman spectroscopy; and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis was applied to cross-sections. The results showed the ubiquitous presence of brochantite Cu4(SO4)(OH)6. Antlerite Cu3SO4(OH)4 is also occasionally present. Residues of an past conservation treatment (Incralac®) and of proteins were detected by μFTIR. Laser cleaning tests were carried out with an El.En. Combo laser, both in long Q-switched and short free-running regimes. Evaluation of the effects of cleaning was carried out with a portable microscope and a reflectance colorimeter. Moreover, a portable FTIR spectrometer was used in order to evaluate the presence of coating residues and corrosion products after cleaning. Electrochemical impedance spectroscopy was used in situ on a selection of the tested areas in order to characterize the effect of laser cleaning on the rate of corrosion. A specially designed contact probe was used for measurements in the frequency range 100 kHz–10 mHz both before and after cleaning.

Laser Ablation of Primer During the Welding Process of Iron Plate for Shipbuilding Industry

Pre-construction Primer (PCP) is an epoxy resin charged with a zinc powder, applied at low thickness to minimize rusting of steel plates during storage and fabrication in shipbuilding industries. In this material, the zinc, in contact with the iron support, acts as a sacrificial anode protecting the surface from corrosion. However, this coating is problematic when the steel plate requires to be welded. In fact, the solid polymeric coating sublimates when exposed at the high temperatures due to the welding process, producing porosity in the welding bead. Different methods can be used to remove the primer before the welding: brushing, sand or ice blasting, waterjet, chemical solvent and laser cleaning. In this paper, laser cleaning tests were carried out by etching a 10x10 mm2 surface of primer coated steel plate, using a 30W Q-Switched Yb:YAG fibre laser. The cleaning tests were carried out varying the scan speed, the pulse power and the distance between two consecutive beam travel (Step). From the treated surface analysis, the percentage of cleaned area was obtained and the process parameters were correlated to the percentage of cleaned area. The process window where laser cleaning could be successfully performed and the maximum process speed were individuate. Finally, observation about the energy consumption and the energy efficiency were reported.

Research into methods of cleaning silicate sandstones used for historical monuments

The cleaning of monuments ranks among the most critical processes in monument restoration, both from an aesthetic and a technological point of view. This article deals with research into the cleaning methods used for the removal of soiling firmly sticking to fine-grained silicate sandstones. The work contains petrological characterization of the substrates and the modes of soiling deposited on the surface. For the cleaning tests, two types of laser have been used (Q-switch and short free running), micro-abrasive cleaning using two different abrasives, and chemical cleaning based on ammonium fluoride. The effects of fluency, frequency, pre-moistening, and the type of device have been examined within the laser cleaning tests. These results have been compared with the results of the abrasive cleaning and chemical cleaning tests from the point of view of sensitivity to substrate, cleaning efficiency and rate of controllability. To evaluate the tests we have used a visual examination of the surface, microscopic examination of the surface and polished sections, and electron microscopy. After the cleaning tests, the changes in the physical properties of the surface were examined.

Laser-assisted cleaning of beryllium-containing mirror samples from JET and PISCES-B

A set of seven polycrystalline mirror samples retrieved from the JET tokamak has been cleaned in vacuum using a pulsed laser system. The surfaces of samples exposed to plasma during 2008–2009 campaigns as part of the second phase of a comprehensive first mirror test contained a mixture of carbon, beryllium and tritium. For this reason, the samples were treated in a vacuum chamber constructed specially for this purpose. In some cases mirrors show an increase of the specular reflectivity after cleaning, though beryllium and carbon deposits were not fully removed. Additionally, three samples coated in PISCES-B with a 110–120nm beryllium layer were subjected to laser cleaning tests as well.

Study of the laser cleaning on plaster sculptures. The effect of laser irradiation on the surfaces

The focus of this paper is to study the effects caused by the laser irradiation on nineteenth and twentieth century plaster sculptures. Before applying the laser cleaning on the sculptures, it was tested on samples prepared in laboratory according to the results of the scientific investigation carried out on the selected works of art. The characterization of the surface finishing materials of the sculptures was performed by Fourier Transform Infrared spectrometry (FTIR), X-ray Fluorescence spectroscopy (XRF), UV fluorescence photography, and internal micro stratigraphic analysis. Regarding the finishing materials, shellac, zinc white, siccative oil and proteins were found on the surfaces. The results of the scientific investigation, together with the examination of the ancient technical manuals, were used to create the laboratory samples to carry out the irradiation tests with laser. The laser irradiation and cleaning tests were carried out with a Q-switched Nd:YAG system. The irradiated surfaces were analyzed before and after the laser tests with the aid of a video microscope and a reflectance spectrophotometer, in order to evaluate the color changes of the surfaces. The possible morphological modifications caused by laser irradiation were also investigated by Scanning Electron Microscopy (SEM) together with ancillary Energy Dispersive Spectroscopy (EDS) elemental analysis. Concerning the laser cleaning test on the samples, in general little color changes were observed both with the 532 and 1064 nm wavelength. Total color changes, expressed as ΔE*, are always small apart from the samples made of shellac and zinc white in linseed oil, as finishing layer. As regards these samples the surface irradiated with the laser greyed lightly, corresponding to a decrease of L* parameter (lightness). SEM imaging of the treated and not-treated samples, both at low and high magnification, does not show evidence of significant morphological differences due to the laser beam irradiation. Starting from these results, some laser cleaning tests were carried out on the original sculptures, putting them in comparison with an aqueous cleaning method. It was found that the laser cleaning removes effectively the dirt layer preserving the original finishing on the sculpures’ surface, whereas the aqueous cleaning system removes also the finishing.

Nd:YAG 레이저를 이용한 금속유물에 코팅된 아크릴수지의 제거 및 표면 특성 연구

Laser cleaning have been found to be a useful cleaning tool to remove contaminants without inducing damage to the substrate and making secondary pollutant. In this study, the effect of Nd:YAG laser cleaning system, emitting at 1064 nm and 532 nm, on acrylic resin applied onto copper coupons and pieces of bronze was investigated. The samples after laser cleaning tests were examined using microscopy, FT-IR, SEM-EDS. As a result, the acrylic resin could be removed from most of the samples at low laser energy density. Laser wavelength 532 nm was more effective than 1064 nm because of using lower laser energy density, which could reduce heat damage to substrates. Although the acrylic resin was easily removed, it revealed melted surfaces and removed bronze patina which must remain. The problems should be solved by future studies using different laser system or laser wavelengths.

Novel approach to the microscopic inspection during laser cleaning treatments of artworks

The present work focuses on the potential of 3D digital microscopy for assessing micro-morphological features during laser cleaning treatments of artworks. This application requires preliminary optimization studies aimed at defining operative irradiation parameters and practicable degree of cleaning, as well as in situ diagnostic assessments during the restoration work. To this goal, we developed and tested a dedicated 3D digital microscope by implementing the "shape-from-focus" technique. The significant potential of this instrument, which provides textural and chromatic information, was proven for the phenomenological characterization of black crust removal from stones, earthy concretion from bronzes and dark varnish from easel paintings. Comparative measurements using 3D digital microscopy and contact microprofilometry were performed after laser cleaning tests of prepared samples, genuine archaeological bronze artefacts and a stone sculptural element from Florence's Dome. The results achieved demonstrate the effectiveness and reliability of the novel approach and the advantages it provides with respect to alternative techniques, which will allow the methods to be used in the wider restoration community.

Laser assisted removal of synthetic painting-conservation materials using UV radiation of ns and fs pulse duration: Morphological studies on model samples

In an effort to establish the optimal parameters for the cleaning of complex layers of polymers (mainly based on acrylics, vinyls, epoxys known as Elvacite, Laropal, Paraloid B72, among others) applied during past conservation treatments on the surface of wall paintings, laser cleaning tests were performed with particular emphasis on the plausible morphological modifications induced in the remaining polymeric material. Pulse duration effects were studied using laser systems of different pulse durations ( ns and fs) at 248 nm. Prior to tests on real fragments from the Monumental Cemetery in Pisa (Italy) which were coated with different polymers, attention was focused on the study of model samples consisting of analogous polymer films cast on quartz disks. Ultraviolet irradiation is strongly absorbed by the studied materials both in ns and fs irradiation regimes. However, it is demonstrated that ultrashort laser pulses result in reduced morphological alterations in comparison to ns irradiation. In addition, the dependence of the observed alterations on the chemical composition of the consolidation materials in both regimes was examined. Most importantly, it was shown that in this specific conservation problem, an optimum cleaning process may rely not only on the minimization of laser-induced morphological changes but also on the exploitation of the conditions that favour the disruption of the adhesion between the synthetic material and the painting.

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

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.

Toward an optimised laser cleaning procedure to treat important palaeontological specimens

In previous laser cleaning tests and analyses carried out on fossil bones, we demonstrated the feasibility and effectiveness of the laser approach. Based on these results, we designed a cleaning procedure employing fibre-optic-delivered Nd:YAG laser radiation, integrated with other conventional cleaning techniques, such as micro-sandblasting and chemical cleaning. The procedure has been optimised for application on important specimens, such as the fossil human “skull of Buia”, recently discovered by a research expedition of the Department of Earth Sciences of the University of Florence and presently preserved in the Museum of Asmara (Eritrea). Here, we report laser cleaning tests where this procedure has been applied on samples of other mammalian bones from the Danakil depression and the site of Matassino (Italy).

Laser and chemical cleaning tests for the conservation of the Porta del Paradiso by Lorenzo Ghiberti

In the framework of the preservation project of the Porta del Paradiso, carried on by the Opificio delle Pietre Dure of Florence, we investigated a cleaning methodology based on integrated chemical and laser techniques. This novel approach, which will replace the previous chemical protocol, was aimed at cleaning a number of gilded sculptural elements of the door frieze, without their being dismounted from the bronze framework. To such an end, optimised chemical and laser cleaning techniques were first singly investigated, and then integrated treatments were tested. The critical evaluation of each procedure was achieved through various diagnostic means to characterise the cleaned surfaces from chemical and physical points of view. The analysis demonstrated the various advantages of a laser-based treatment followed by light sodium potassium tartrate poultice application.

The Gate of Paradise: physical optimization of the laser cleaning approach

A methodology for the use of lasers in the restoration of the Gate of Paradise, a gilded bronze artwork by L. Ghiberti, was evaluated theoretically and experimentally. Preliminary characterization of the materials to be laser-cleaned made it possible to estimate the thermal regimes involved and to model the ablation process. Calculations aimed at controlling unwanted heating of the gold film were also developed before laser-cleaning tests on large areas were carried out. Finally, the cleaning tests were critically evaluated by means of instrumental inspection. The practicability of the laser approach, either as a preliminary to gentle chemical cleaning involving lower concentrations of chemical agents and shorter exposure times or as a standalone treatment, was demonstrated.

Laser divestment for natural history museum collections

A series of probative laser cleaning and divestment tests has been performed on a wide variety of the materials encountered in natural history museum collections. These tend to be quite different from the substances customarily encountered in fine art collections. Initial results are shown for laser cleaning of minerals, fossils, wood, ancient textiles, feathers, as well as mummified and frozen tissue. The preliminary results indicate that laser cleaning and divestment may have even more utility in the natural history field than in fine art conservation.