首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 23 毫秒
1.
The possibility to use laser radiation to clean historical objects has been established for several years. A complex case and widely met problem are polychromes. They react (chemically as also physically) very sensitively towards laser radiation. In this study, the reaction of pigments was investigated in dependency on the incident wavelength (Nd:YAG, λ = 1064, 532, 355, 266 nm) and energy density. The chemical and also the physical interactions were investigated. In this work, the following analytical methods were utilised: differential thermal analysis (DTA), colour measurements (CIE-L*a*b*), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). It turned out that the colour change of the pigments can have different origins: they can for instance be induced by laser induced oxidation, reduction or phase changing. Most of the pigments show reactions at very low energy densities (H < 100 mJ cm–2). Overall the fundamental wavelength of the Nd:YAG-laser (λ = 1064 nm) proved to be most suitable, whereas λ = 355 nm shows most influence on the colour change.  相似文献   

2.
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   

3.
The removal of a brass-based paint (purpurin) used in painting gilded wood to cover losses of gold leaf, represents today a difficult task to conservators, who may have to resort to toxic chemical solvents in order to clean the painted surface. This action, due to its nature, is unsuitable for both the conservator and the artwork itself. In this study, a Q-switched Nd:YAG laser system outputting 1 064 nm (infrared), 532 nm (visible, green) and 266 nm (ultra-violet) radiation was used to study the interaction of these wavelengths in a gilded sample surface painted with purpurin. All tested wavelengths interacted differently with the tested surface and, also, the several layers that form the gilded surface (purpurin, varnish and gold) showed different interactions to each wavelength. The ultra-violet radiation (266 nm), in a multi-pulse mode at low fluences, was found to be the most efficient wavelength in cleaning the painted gilded surface.  相似文献   

4.
Laser cleaning has been used to restore the soiled terracotta statues and decorations of the tympanum of the portal of Palos of the Cathedral of Seville in Spain. A simultaneous laboratory study performed on a representative sample helped to identify the optimum laser conditions to remove the dark soiling layer produced by air pollution. It was found that irradiation at 1064 nm with a Q-switched Nd:YAG laser was more effective than the harmonic wavelengths of 532 or 266 nm. LIBS and Raman microscopy gave information on the composition of terracotta and identified the presence of a protective layer made of gypsum and calcite. As detected by Raman spectroscopy, laser irradiation caused the elimination of the carbon component of the soiling layer and the appearance of an anhydrite component in the laser irradiated gypsum layer applied over the terracotta substrate for protective purposes. Local heating of the surface caused by laser irradiation at 1064 nm, the laser wavelength used for restoration of the portal, might be responsible for a process of partial dehydration of gypsum into anhydrite.  相似文献   

5.
The historical paper samples from XIII–XIX c. are characterised by means of techniques of the optical spectroscopy. The influence of pulsed laser cleaning by means of the Q-switched Nd:YAG laser at 532 nm on the spectra and also cleaning results of stained paper documents are reported and considered. In the absorption spectra, the minima around 280 and 370 nm are identified and luminescence reveals a characteristic band centred around 430 nm. The laser cleaning diagnosed by the recording of the LIF spectra with 266 nm excitation shows a profile of increasing intensity and preserved structure. The LIPS spectra reveal sharp emission lines recorded at 612.5, 644.2, 646.5, 671, 714.9, 720.2 nm (Ca I), 589.4, 616.4, 780 nm (Na I), and 766.5: 769.9 nm (Mg I) which are ascribed to the surface contaminations. The intensity decrease of these peaks is in accordance with successive laser pulses and monitors the cleaning progress of the stained paper.  相似文献   

6.
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   

7.
The paper presents the use of laser radiation for cleaning of beeswax treated granite stone. In the early sixties, prestigious restorers decided to apply molten beeswax on the granite surface of valuable monuments with the aim of preventing the erosive action of atmospheric agents. An interesting example of this treatment is the Renaissance Frieze in the Cloister of the Cathedral of Santiago de Compostela in Galicia (Northwest Spain). With time, salt accumulation beneath the beeswax layer has caused an intense surface disintegration of granite. Conventional cleaning methods can destroy sculptured details of these emblematic monuments. For this reason, excimer laser cleaning has been chosen as a promising non contact, selective and environmentally friendly cleaning technique to be studied.The cleaning tests have been carried out using an excimer laser (ArF, 193 nm), with fluences between 0.5 and 2 J cm−2 pulse−1 and a spot area of 0.025 cm2. Samples representing beeswax films over Roan granite have been irradiated and their degree of cleaning has been studied as a function of the number of pulses and the laser fluence.Cleaning efficiency has been evaluated by FT-Raman Spectroscopy, allowing to establish the beeswax ablation threshold and the ablation rate.Excimer laser cleaning allows a progressive and controlled removal of a few tenths of micrometers of beeswax per pulse without damaging the underlying granite stone.  相似文献   

8.
A series of tests has been conducted to evaluate the potential for using a Q-switched Nd:YAG laser (wavelengths 1 064, 532 and 266 nm) to clean both new and naturally aged cotton textiles. Tests have been carried out on i) plain weave and velvet cotton and ii) new and naturally aged cotton samples to investigate the possible roles of weave structure and ageing in the cleaning process. Cleaning trials have been carried out on artificially soiled new cotton and compared with results obtained using traditional cleaning techniques: wet cleaning and organic solvent cleaning. Cleaned surfaces were examined using optical and scanning electron microscopy.  相似文献   

9.
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   

10.
Unlike the traditional methods of silk restoration based on the application of synthetic polymers, transglutaminase-mediated polymerization was used as a compatible and innocuous method to reinforce the aged silk fabrics. Artificially aged (dry thermal ageing) silk samples were restored using this method. The optimal experimental conditions of the treatment were determined by orthogonal experiment. The effects of the reaction on silk fibers were investigated by tensile tests, TGA and SDS-PAGE. The results showed that tensile strength, elongation rate at breakage and thermal stability of the silk samples were remarkably improved by using this method. Biopolymers with a molecular weight of more than 260 kDa were formed in the reaction. From the results of this study, the potential of transglutaminase-mediated polymerization to restore historic silk was demonstrated.  相似文献   

11.
During the 13th and 14th centuries, the commune of Massa Marittima successfully exploited the nearby base-metal mines (copper, lead and silver). Several smelting sites were active. Twenty-seven slag specimens were sampled at Marsiliana, Arialla and Rocchette Pannocchieschi. Slags have been analysed by X-ray fluorescence spectrometry, X-ray powder diffraction, optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. The slags from the three sites differ in chemical composition. The most abundant pyrometallurgic phases in the glassy matrix are calcic clinopyroxene, kirschsteinite, melilite, accompanied by spinel, wüstite, sulphides, metals and metal alloys. The three sites produced more than 2000 t of copper, 6000 t of lead and 2 t of silver. Copper was mostly smelted at Marsiliana, and silver-bearing lead was smelted at Arialla and Rocchette Pannocchieschi. The minerals underwent only a mild roasting prior to smelting. Flux lime was added to the mineral charge, and the resulting viscosity index of the melts (from 0.9 to 3.7) assured effective metal segregation. Furnace temperatures reached 1150–1300 °C.  相似文献   

12.
Potentials and limitations of the near-UV pulsed laser cleaning of parchment (wavelength 308 nm, pulse duration 17 ns) are demonstrated by the application of scanning electron microscopy (SEM), colour metrics and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) at model contamination/pigment/parchment systems. Pigment-binder systems stable and unstable against near-UV laser treatment could be identified. A chemical degradation threshold fluence of a goat parchment model substrate was determined which practically coincided with its ablation threshold fluence. This indicates that the fluence range of destructionless laser cleaning at 308 nm is almost not impaired by chemical modfications below the ablation limit. Nevertheless, spectroscopic diagnostics are necessary to guarantee destructionless cleaning for practical cases where the chemical conversion threshold fluence deviates from the ablation threshold to lower values.  相似文献   

13.
Acetic and formic acid vapors emitted from woodwork in historical organs are very important corrosive agents for lead pipes. These acids are slowly released from the wood both during playing and when the pipes are silent. To inhibit this emission process, the wood surface can be modified, by creating a protective layer with alkaline features. However, a coating of wood is not recommended since this could modify the appearance and create a layer not perfectly compatible with the substrate. For this reason, we propose to use some innovative nanotechnology that has been successfully applied for the deacidification of wood samples coming from the Vasa shipwreck. Application of calcium (or magnesium) hydroxide nanoparticles, with sizes ranging from 30–150 nm, allowed a homogeneous distribution of particles through the surface layer of wood simply by soaking (or spraying) it in a alcoholic (or mixed with less polar solvents) dispersion of nanoparticles. Nanoparticles do not modify the wood appearance and distribute randomly within the first layers of wood. The small size of particles accounts for the high reactivity with CO2 from the air, to give the alkaline reserve of carbonates that provide high efficacy in the neutralization of gaseous acids. The emission of volatile organic compounds (VOC) from the treated wood was determined by using an emission test cell, Field and Laboratory Emission Cell (FLEC). The results show that the emissions of acetic acid vapor from nanoparticles treated wood was very low (< 70 μg/m2 h) during the first 13 month. In contrast, untreated wood emitted high concentrations of acetic acid vapor (200–400 μg/m2 h).  相似文献   

14.
In a parallel study, it has been shown by comparison of successive TV-holography campaigns that murals in the convent of Müstair (Switzerland) have progressively detached from their substrate over a time interval of 5 years (J Cult Herit 2009). Here, we focus on the dynamics of the ongoing detachment processes. In order to regularly measure small surface displacements in situ over a long duration of several years, a new method that we call Mirror Micrometry (MM) has been designed and implemented. This method monitors the reflection of a light beam by a mirror that is mounted to the surface of interest for the duration of the experiment. The mirror is designed to rotate about a pivot as small displacements in the detaching surface occur, thus deflecting the reflected light beam. Measurements over more than three years in the Convent Church and in the Holy Cross Chapel reveal various types of surface displacement perpendicular to the wall surface. These are correlated with relative humidity (RH) changes in the room climate. Reversible short-term variations of approximately ±5–10 μm occur with periods of one to several weeks and relate primarily to weather changes. Reversible long-term variations of ±5–10 μm correspond to averaged seasonal humidity changes. Irregular and irreversible movements in increments of 20–30 μm record very localised progressive detachment steps. A semi-quantitative correlation of approximately 1 μm surface displacement per 1% RH change is calculated. Based on the fact that nearby measuring points can simultaneously move in opposite directions, a geometric model is drawn to explain deformation by hygric swelling and shrinking of different shapes of detached layers.  相似文献   

15.
Calcium hydroxide is typically used in Cultural Heritage conservation for superficial protective treatments thanks to its conversion into calcium carbonate. Calcium carbonate is, in fact, compatible with many carbonate-based architectonic surfaces, because its characteristics are similar to those of the restored materials. In order to improve calcium hydroxide treatments, Ca(OH)2 particles with sub-micrometric dimensions (nanolimes), are synthesised by a chemical precipitation process: a sodium hydroxide solution, used as precipitator, is added, drop by drop, to a calcium chloride one. In this paper, a nanometric calcium hydroxide, to be used in stones treatment, is produced adding in the initial solutions a surfactant agent (Triton X-100); the solutions are then mixed together simultaneously, drastically reducing the time needful for preparation. Different contents of surfactant are employed, and the influence on particles dimension and carbonatation process is analysed too. The obtained Ca(OH)2 nanoparticles are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED). The Ca(OH)2 nanoparticles are regularly shaped, hexagonally plated and with side dimensions less than 200 nm: in particular, increasing the surfactant content, the particle dimension reaches values until 20 nm. Comparing nanolime suspensions obtained without and with the addition of the surfactant agent, the last ones have comparable, if not better, performances in terms of average particle size and morphology, crystallinity and reactivity. Afterwards, the alcoholic nanolime suspension obtained by using Triton X-100 is applied on some natural stones; in fact, the aim of this section is to compare the obtained results with those achieved using a nanolime synthesised without the surfactant agent. To evaluate the treatment effectiveness in a preliminary way, standard tests are performed and compared with the same tests previously obtained by the nanolime synthesised without the surfactant agent: “Scotch Tape Test” and capillarity test.  相似文献   

16.
The pigments, organic materials and techniques used on a post-Byzantine icon of St Nicholas were determined by means of several micro-analytical techniques. The icon painter covered the leather support with silver leaf about 3 μm thick to create a smooth working surface. Animal glue was used to secure the leaf to the leather, and FTIR spectroscopy has identified another layer, 30–60 μm thick, of the same material applied as a primer above the silver. Above that, a layer of lead white covering the entire surface creates a white substratum serving the same purpose as the gesso on a wood panel. The colour palette, determined by means of scanning electron microscopy and FTIR spectroscopy, is very simple. Only seven colours were identified: lead white, caput mortuum, red and yellow ochre, cinnabar, carbon black and smalt. As far as we know, this is the first time that smalt has been found on a Byzantine icon. Since smalt was chemically synthesised only after 1500 AD, it may be concluded that this icon was painted after the end of the 15th century. Beeswax was used as a protective varnish.  相似文献   

17.
The focus of this work is the wood polychrome model of the church of S. Maria della Consolazione in Todi, an artefact whose author and historical events are not completely known except a general reference to the construction period of the church (1508–1607 AD). In this study, original and additional materials were examined in order to provide a deeper understanding of the painting and assembly techniques, and a greater awareness of how well preserved the object is, as well as an analysis of previous preservation and conservation interventions. The samples from the painted surfaces were examined by means of micro-Raman spectroscopy, fourier transform infrared (FTIR) spectrometry and internal microstratigraphic analysis. Thin sections of the wood samples were examined under an optical transmission light microscope in order to identify the botanical species. The results shown in this paper suggest the possibility that the original painted layers are made of calcium carbonate white, red ochre and indigo and they were applied by protein binder without any ground layer. Some non-original pigments were found on the model surface like Prussian blue and chrome yellow. Concerning wood components, poplar was characterized both in the original and non-original parts of the model whereas pine species were detected only in the restoration elements.  相似文献   

18.
The cross-linking processes of three drying oils (poppy, linseed, walnut), a class of organic compounds very important in the field of artworks, were studied by means of 1H-NMR spectroscopy, following the change of the protons signals when oils are heated at 60 °C in the presence of air or nitrogen gas. This preliminary information is particularly important to identify the presence of drying oils within a solid painting film. We demonstrated that it was possible to study these films by swollen-state NMR, an innovative spectroscopy method that can directly analyze very small semisolid samples instead of solutions. The main advantages of this method are the short time of analysis, the possibility to analyze samples without any preliminary treatment, and the small quantity of the sample required. Therefore, swollen-state NMR technique was used to characterize three real painting films: in this way, we succeeded in recognizing in real paintings specimens the presence of drying oils employed as binders, avoiding any interferences due to other organic compounds acting as binding agents, like waxes or egg-yolk media.  相似文献   

19.
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   

20.
Durability is one of the most important engineering properties of cultural heritage monuments. For the purpose of the preservation of structures for future generations, the causes of damage should be determined for the proper choice of type and location of strengthening. The condition of the foundation is difficult to determine without an extensive investigation which is critical because most often the cause of damage is found in such foundations. Geotechnical investigation techniques require the damage and destruction of a building's surroundings or the damage of a foundation with a boring device. Non-destructive methods, such as geophysical methods, are less reliable and the results of such investigations must be combined with the results of subsurface exploration. This paper is a presentation of results achieved through the monitoring of the activity of a number of joints on the Cathedral of St. Lawrence in Trogir, Croatia, which is a cultural heritage monument protected by UNESCO. Excavations for the purpose of flagging replacement in the zone around the east frontage were made in 1979. A probe beneath the main apse uncovered a water cistern where the connection between the mid and north apses is located, and instead of a staggered foundation, a wall with a depth of more than 2.2 m beneath the flagging was discovered. With respect to the given that churches were built on existing ones, it is possible to assume that this is a wall of the late-antiquity church described by Constantin Porfirogenet in the 10th century, built on and later adapted to the foundation for the new structure. The displacement in time of the construction elements of the cathedral were measured and recorded using non-destructive methods. Fissure displacement behaviour, air temperature and air humidity were monitored. The monitoring of the air humidity did not lead to any useful conclusion, so it was quickly dismissed. Observations of data were performed during two periods with an interruption between the two caused by insufficient monetary resources. Data from almost 8 years of continuous measuring are available. The aim of this paper is to present the data of the measured fissure displacements which were correlated with air temperature changes and mathematical models which were based on statistical analysis. Correlation coefficients show that the analysed fissures react to the air temperature changes with different intensities. The obtained data lead to the conclusion that the causes of the structural damage are not found within a displacement or failure of the foundations. Instead, the causes of the damage were found in other parts of the structure.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号