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1.
The development of laser cleaning as a conservation treatment has imposed a need for the evaluation and assessment of other cleaning techniques. The use of more traditional methods like abrasive cleaning, steam cleaning and chemical cleaning has relied so far on visual assessment, unlike much of the research applied to laser cleaning. A conscientious use of these cleaning methods requires their assessment as well as the need for a comparison based on a common methodology. A topographical assessment of laser cleaning, abrasive cleaning, steam cleaning and chemical cleaning (using hydrofluoric acid, ammonium carbonate and EDTA) is presented. Topographical variations induced on marble, oolitic limestone and architectural terracotta surfaces are assessed by means of light interferometry, showing the potential of this non-contact and non-destructive technique for surface studies in conservation. The comparison between cleaning treatments is based upon key parameters associated with cleaning surfaces. The aesthetic impact of these treatments is verified by means of optical microscopy and quantified by colour measurement. Chemical analysis of the cleaned surface (EDS) is performed to investigate the removal of surface pollutants and the presence of residues. Finally, petrographical analysis was used to investigate the removal of pollutant layers and its effect on surface texture. 相似文献
2.
《Journal of Cultural Heritage》2014,15(3):258-265
Lasers have served as cleaning tools for historical objects and artworks for about 40 years. In many cases, superior results of laser cleaning were achieved with respect to traditional methods. In this technique, contaminations on the surface of the object are ablated by laser irradiation. In order to apply laser cleaning method to fragile materials such as paper made of cellulose or parchment, heat deposition to the bulk should be minimal, to prevent damage. In this work, it is demonstrated that laser pulses with femtosecond (fs) duration can exhibit non-thermal ablation of contaminants on paper samples. In particular, laser cleaning studies are concentrated on paper samples with sizing. Fs laser cleaning is performed on artificially soiled and aged samples, as well as on historical ones. The laser used in the experiments has pulse duration of 550 fs and 1030 nm center wavelength. The fluence of the laser is varied and the post-cleaning statuses of samples are investigated. The analyses are color changes, fiber integrity, chemical composition changes and mechanical strengths. These results show that fs lasers can be very efficient in cleaning paper samples, yielding minimal discoloration and no damage to fibers distinguishable on microscopic examination. The presence of sizing also provides further protection against possible side effects. 相似文献
3.
Laser cleaning of ancient marble and stone monuments is nowadays a well-accepted procedure in conservation. Operators and specialists are presently divided between those giving maximum confidence to this method of cleaning and others who, in contrast, are strongly critical and emphasise possible drawbacks and damages caused by laser. As any other method of cleaning, laser also offers advantages but at the same time is limited by drawbacks. Most conveniently, it should be integrated with the other methods. On the basis of the above considerations, the authors are proposing a combined procedure using laser cleaning as a first step – in this way removing the relevant part of black gypsum encrustation – followed by chemical methods as a final step. The latter, conveniently, could be accomplished by means of anion exchange resins, better than ammonium carbonate. An experimental check-up was made of four different methods applied on three different lithotypes on the façade of the Florentine Cathedral. Laser, micro-sandblasting, ammonium carbonate and sodium EDTA were the cleaning methods compared, whilst Carrara marble, green Serpentine (Verde di Prato) and a red limestone were the three lithotypes. Results are commented by showing differences in the advantages and drawbacks among the different methods on the various lithotypes. 相似文献
4.
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. 相似文献
5.
Within the framework of a European project, three cleaning laser devices are tested to evaluate the influence of different parameters on stone cleaning rate and efficiency. The project objective is to design a large surface-cleaning laser. One of the devices is a prototype with some technological improvements compared to the lasers used today for restoration. The tests are performed on limestone and sandstone covered with various dirt layers. The influence of fluence, water spraying, spot area, frequency, as well as particle emission rate is investigated. Results allow a comparison of the importance of each parameter and confirm the increase in cleaning speed of the new prototype. Nevertheless, it can be concluded that an automatic device will be suitable to attain a cleaning speed competitive with other traditional cleaning techniques. 相似文献
6.
Within the conservation programme of the mausoleum of Theodoric, located in Ravenna, Italy, we applied a new cleaning procedure based on the use of a recently developed Nd:YAG laser system, suitably equipped in this case with long optical fibre cables for the transmission of laser radiation to work sites on the façade. The intervention of the laser technique was required to complete the cleaning of a decoration surrounding the monolithic dome, after conventional cleaning methods had been applied with unsatisfactory results. Preliminary laboratory analyses on stone samples collected from the dome and subjected to laser treatment indicated that this technique was effective and could fully preserve the lime–Ca oxalate film existing below the thick layer of black crusts. Before starting the operative phase on the mausoleum, it was necessary to solve the practical problem of keeping free access to the monument during cleaning operations, which hindered the location of the laser in close proximity to the sites to be cleaned. This was achieved by preparing long fibre cables (up to 50 m) which permitted the successful completion of the cleaning while leaving the laser body far away from the dome. 相似文献
7.
Vassilis Papadakis Afrodite Loukaiti Paraskevi Pouli 《Journal of Cultural Heritage》2010,11(3):325-328
This study aims to introduce a new spectral imaging methodology that can be used to monitor on-line, non-destructively and in situ the cleaning level of pollution encrustation on stonework. The suggested technique is based on the optical properties of monochromatic light penetration in matter. The calculated differences of images, obtained at two different spectral bands, could reliably map the depth of cleaning. This novel approach was tested in the laboratory during laser cleaning trials on polluted stonework enabling high accuracy measurements (such as the detection of thin crust layers remaining on the under-cleaned marble surfaces). However, it may also apply for the monitoring of any other cleaning technique (micro air-abrasive, etc). A detailed presentation of the results will be demonstrated while the potential of its wide application on everyday conservation practice on stonework will be discussed. 相似文献
8.
The German Federal Foundation for the Environment (Deutsche Bundesstiftung Umwelt) is one of Europe's largest organizations of its kind. It supports innovative, exemplary projects for the protection of the environment and of national historic monuments and cultural landscapes. All projects are set up to provide a platform for researchers, craftsmen and restorers to find a common solution to difficult problems in conservation practice. More than 360 projects have been funded since 1990. Two recent projects deal with laser cleaning, one for stone and the other one for stained glass windows, the latter being presented here. This publication gives an overview on cleaning problems on stained glass windows and the project methodology. The interdisciplinary approach of the project provides the possibility of including experts in different fields to examine perspectives and limits of laser cleaning for stained glass windows. Two other publications in this issue (LACONA III) give selected results on cleaning experiments achieved within this project. 相似文献
9.
SMART CLEAN is an innovative Nd:YAG laser system that has been designed to optimize laser cleaning procedures, especially for the treatment of altered stone surfaces. The project, originated by the co-operation of researchers and enterprises involved in optoelectronics system development, was aimed at improving the intrinsic features of the laser source, as well as some practical aspects, in order to facilitate laser application in the restoration yard. Emission characteristics were suitably tailored to obtain effective removal of alteration layers, and to minimize possible side effects. In particular, the pulse duration of the SMART CLEAN laser was set at 20 μs, by means of a proprietary design of the power supply. This was in order to reduce the risk of both mechanical and thermal damage to the artwork substrate, which is more likely to occur with short and long laser pulses, respectively. Moreover, this pulse duration permitted a reliable transmission of high laser energy through long optical fibres (50 m), which allowed easy cleaning operations on façades. The laser system was tested on a large variety of lithotypes and in operative cleaning interventions on Italian monuments. 相似文献
10.
The hewn sandstone and ornamental figures of the Albertino Chancel, built around the mid-14th century, are covered with black encrustations of plaster and carbon deposits, often several millimetres thick. Their removal constitutes one of the main objectives in the conservation of the precious materials of the cathedral. The Nd:YAG laser method cleans the original surface of hardened encrustations without damaging or affecting the old coloured plasters and without affecting the centuries-old patina. Laser-Tech GmbH, founded by two expert restorers from Austria and Italy, is specialised in large-scale projects and, regarding the present project for the chancel, has managed to combine the sensitivity of the preserver with the laser technology applied to large surfaces. The present project concerning St. Stephen's Church comprises over 2000 m2 of stone surface treated only with laser systems, by groups of qualified restorers trained at Altech to use such instrumentation on artistic historic surfaces. 相似文献
11.
The Church of the Maddalena was built between 1763 and 1778 by Tommaso Temanza. The building has a central plan and is surmounted by a copper-covered brick masonry dome. The conservation work conducted on the façade has highlighted the superb quality workmanship of the Istrian stone surfaces, which feature extremely fine grain, perfectly regular tooth-chiselling. This finish has led, however, to very specific conditions of decay and laser treatment provided appreciably better results than traditional chemical and mechanical methods. In addition to laser, however, other methods of cleaning were used in order to find the best response to each of the various situations encountered. Indeed it should be emphasized that in restoration it is often appropriate to exploit the potential of several systems, combining their action on the basis of careful preliminary analyses. 相似文献
12.
Laser cleaning was applied to remove aged and soiled oil paints of the 19th century from weathered, brittle sandstone surfaces. In contrast to other tested cleaning methods, the laser technique allows the removal of the oil paint layers with a minimum of material loss in brittle zones. The cleaned test areas have been investigated by optical and scanning electron microscopy as well as by colour measurements. The investigations have shown that the dirt and the oil paint layers can be removed by laser cleaning without affecting the original sandstone surface and that the pores can be opened again. The brown shade after cleaning is not caused by laser interaction with the sandstone surface but by historic impregnation with linseed oil. Immediately after cleaning, a treatment with chemical consolidants is necessary to preserve the brittle sandstone surface. Sustainable consolidation could be problematic in some areas, because the laser cleaning also preserves heavily damaged, crumbling zones of the carvings. For economic reasons, laser cleaning should be applied only in the most endangered zones of carvings and combined with classical methods (organic solvents and scalpel). 相似文献
13.
A collaborative project between the Materials Department of Imperial College, the Victoria & Albert Museum, Natural History Museum and the Tate Gallery was initiated with the objective of introducing laser cleaning in these London-based museums and establishing a long-term research collaboration. An access to these material conservation departments means that materials like traditional statuary materials, heavily corroded metals, ivory, palaeontological samples, textiles, stained glass, plaster and some modern materials can be used to investigate the usefulness of laser cleaning and study their effects using a wide range of analytical techniques. 相似文献
14.
《Journal of Cultural Heritage》2014,15(6):602-608
Ground wood cellulose paper exhibits a practicable cleaning laser fluence window during middle-UV radiation processing. In this case, a minimum dose volume density should be applied. However, cleaning of bleached cellulose paper is accompanied by strong yellowing and destruction. The presence of charcoal graphite particulates shows substantial influence on the yellowing with increasing coverage. 相似文献
15.
Farideh Fekrsanati Stefan Klein Jens Hildenhagen Klaus Dickmann Yiorgos Marakis Aleka Manousaki Vassilis Zafiropulos 《Journal of Cultural Heritage》2001,2(4):187
The application of lasers for the removal of superficial deposits from historic stained glass is a comparatively new field of scientific interest. Experimental studies concerning the behaviour of glass substrates and the corresponding superficial deposits towards different laser wavelengths were carried out. The experiments were performed using wavelengths of λ = 193 nm (ArF-Excimer), 308 nm (XeCl-Excimer), 355 nm (Nd:YAG third harmonic) and 1 064 nm (Nd:YAG fundamental) in comparison to λ = 248 nm (KrF-Excimer). This comparison is due to the fact that the present knowledge is based on the 248 nm wavelength. Specially prepared model glass samples representing the original fragments and samples of organic polymers (formerly used as a protective material for historic stained glasses) were used to study the effects of laser radiation and were subsequently characterised by optical microscopy. 相似文献
16.
A medieval wooden panel chamber was rediscovered during reconstruction of the Tetzelhouse in the Saxon town of Pirna. Ceiling and walls are made from 600-year-old fire wood panels fitted together. The complete removal of layers (limewash, plaster, glue and dirt) from the wall panels was the precondition for conservation of the wood panels and for the restoration of the wooden panel chamber. The cleaning was carried out with a pulsed Nd:YAG laser after basic investigation of ablation mechanisms of the layers on the old wood. All layers of the different materials were removed both from the normal surface and out of depressions and woodworm holes with a special range of laser parameters, without damaging the wood. Within this range of parameters the laser cleaning is a self-limiting process. The health hazard from emitted waste products were determined and checked with work place measurements. The laser cleaning of the wooden wall panels was completed in March 1999. A uniform visual impression of all panels was obtained with a warm wooden colour tone. 相似文献
17.
An investigation has been undertaken into the effect of wavelength in the laser cleaning of parchment. Tests have been carried out using the fundamental (1 064 nm), second harmonic (532 nm) and fourth harmonic (266 nm) outputs from a Q-switched Nd:YAG laser (pulse length 10 ns). Initial testing was carried out on new parchment to characterise the damage caused by overcleaning. The fluence and wavelength of the laser beam were then optimised so that any damage to the parchment or loss of ink during dirt removal from a late eighteenth century parchment document were minimised. The cleaned surfaces were examined by optical and scanning electron microscopy and analysed by measurement of the shrinkage temperature of cleaned collagen fibres. The laser-cleaned areas were compared with uncleaned areas and areas cleaned by traditional techniques. 相似文献
18.
The self-limiting effect during laser cleaning only occurs in a limited amount of specific applications in restoration (e.g. removal of black crust from white marble). In all the other cases, a control of the removal process will be necessary either by the operator himself or by the employment of sensor equipment. Various methods, mainly spectroscopic (e.g. LIBS), have been investigated and proposed by others. Despite the fact that these have been shown to be promising, they all have in common rather high investment cost close to that of the cleaning equipment. Furthermore, this highly sophisticated control equipment is not easy to handle by conservators in practice. As an alternative low-cost method, we employed a simple photodiode to detect the scattered light from the irradiation area on the artwork surface. In many cases, this signal contains several pieces of information on the layer just being removed. The scattered radiation detected by the photodiode originates from the laser-induced plasma as well as reflected laser radiation. A separation, if necessary in order to separate the information, is possible by spectral filters. First applications during laser cleaning of corroded metal, encrusted glass and stone were promising. It has turned out that there is a distinct influence on the scattered light amplitude or even the pulse-bandwidth once the laser has removed the encrustation completely. The corresponding signal can be used in a closed loop control or for online monitoring. 相似文献
19.
Rock weathering is defined as the process of rocks alteration as a result of the adjustment of its internal constituents by the action of physical, chemical and biological factors, to the prevailing conditions of the atmosphere and in the environment. In humid polluted areas “red weathering” is one of the major deterioration forms that characterize most granitic rocks. Several intervention steps are required to remove and treat all surfaces affected by this form. It is one of the most aggressive forms of deterioration which are essentially composed of some complex species of clay minerals “Kaolinite, Illite, Montmorillonite and Tosudite”, in addition to some species of salts as “Gypsum” pigmented by “Hematite” as a colorant. After several investigatin techniques, these crusts need several intervention and conservation steps to remove and eliminate the aggressive effects resulted from the red crusts through three essential steps: “cleaning, gap filling and strengthening and stabilizing”. After evaluating all materials and methods that were performed by “DBN, SEM, EDX, and AAS”, the present study suggests that the most suitable cleaning methods are composed of three essential steps “dry and vacuum cleaning (DVC), ultra-sonic cleaning (USC), poultice cleaning (PC)”. Furthermore, the elected gap filling material composed of “Araldite AY-103” mixed with “Granite powder as petro-filler.” Finally, different evaluation methods proved that “Wacker H” is the most suitable strengthening and stabilizing material for consolidation purpose. 相似文献
20.
A KrF-excimer laser operating at λ = 248 nm was used for basic studies in cleaning ancient glass surfaces. For irradiation a mask projection technique was applied. A modified optical set-up was designed using cylindrical lenses for large area removal by line scanning. Previous investigations revealed insufficient knowledge about interaction processes between UV-laser radiation and individual surface layers of encrusted historical glass. Thus, first detailed studies were carried out on special model glass samples simulating the behaviour of historical glass. The potential of removing crusts, bio layers as well as layers of different conservation materials (due to former conservation work) were examined. The avoidance of damaging material such as gel layers, paint layers or the bulk glass was of great importance. Removal rates and thresholds for the materials mentioned above were carried out. The collected data enables a comparison and evaluation of the feasibility for the removal of superficial layers from historical glass artefacts. The results indicate that in some cases a closed loop process control will be necessary to avoid over-cleaning. 相似文献