Nd:YAG laser effects on inorganic pigments

The effects of a Q-switched Nd:YAG laser irradiation on a group of supports, painted with six different inorganic pigments, was investigated. The pigments were chosen from among the most utilized on painted historical surfaces: red ochre, yellow ochre, chromium green, ultramarine azure, white chalk and carbon black, and they were distempered with two binders – linseed oil and gypsum – on primed wood panels. The pigments were characterized by means of X-ray diffraction and Fourier transform infrared spectroscopy. Chromatic characteristics, chemical composition and surface morphology of the painted layers were investigated before and after the laser irradiation. Three different fluences were used to detect the correlation between laser parameters and changes in painting layer characteristics.     

The effect of Nd:YAG laser radiation on medieval pigments

Very often traces of paint and pigment have been found on medieval sculpture. Presently, little is known about the effects of laser radiation on polychromy. It is important to protect and preserve these traces during any cleaning or restoration process. The absorption properties of polychrome materials are likely to be different from those of the underlying stone or substrate and as a result special care must be taken to avoid any damaging or discolouring phenomena associated with laser cleaning. Spectroscopic methods (XPS, AES, reflectance spectroscopy) together with optical microscopy, digital photography and X-ray diffraction analysis have been used in a series of experiments on simulated samples of common medieval pigments (vermilion, red and white lead and ochres in linseed oil) on limestone plates, in order to study the reaction of these materials to infrared laser radiation.     

A study of the effect of the wavelength in the Q-switched Nd:YAG laser cleaning of gilded wood

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.     

St. Stephen's Church in Vienna: criteria for Nd:YAG laser cleaning on an architectural scale

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.     

Electronic paramagnetic resonance as a tool for studying the blackening of Carrara marble due to irradiation by a Q-switched YAG laser

Several authors or practitioners have remarked that Q-switched lasers have an immediate blackening effect on mineral pigments such as vermilion (HgS), minium (Pb₃O₄), white lead [2PbCO₃. Pb(OH)₂], malachite [Cu₂CO₃.(OH)₂] and yellow ochre (FeOH₂). A similar blackening effect can also be obtained on veined Carrara marble. This stone contains several trace elements, particularly iron and manganese. The latter is responsible for a particular response in electronic paramagnetic resonance spectroscopy (EPRS). We investigated the effect of a Q-switched Nd:YAG laser irradiation on the EPRS trace of Carrara marble. Further experiments were performed with the same analytical tool on synthetic calcite powders that had been doped with iron or manganese. It appeared that no significant change of EPRS trace could be put into evidence after laser irradiation of both bulk Carrara marble or doped calcite powders, although some samples had actually blackened. It is concluded that the blackening effect is not due to an oxidation of manganese ions. Colour measurements were also performed within the framework of this investigation. They showed that the colour shift to black is proportional to the fluence applied to the stone surface     

UV-laser radiation: basic research of the potential for cleaning stained glass

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.     

Experimental study on the effect of wavelength in the laser cleaning of silver threads

Laser removal of surface contaminants on silver threads was carried out using Nd:YAG laser radiations from near infrared (1064 nm) through visible (532 nm) to ultraviolet (266 nm) produced by frequency harmonic generation. The thread in the museum textile was made of silver and silk in which the silver ribbon wraps the bunch of silk fibres. The goal of this work is to find a feasibility to clean the tarnished silver without any damage of the underlying silk since the conventional chemical treatment is problematic to apply in this specific specimen. From the results, it was found that the laser wavelength of 266 nm is most appropriate to clean the silver surface without causing any damage either to the silver or the silk surfaces while 1064 nm wavelength easily causes damages such as melting and burning to the silver as well as the silk inside.     

Conservation of stained glass windows with protective glazing: Main results from the European VIDRIO research programme

The methodology of protecting the European stained glass windows against environmental risk (e.g. meteorological factors, air pollution, microorganisms) by means of an external glazing is not new. In spite of many scientific studies carried out in the last 20 years, some questions were still up for discussion. The European VIDRIO (2002–2005) project gave an answer to these questions. The research carried out by the different project partners established a new multidisciplinary approach aimed at evaluating the efficiency of the protective glazing systems and their effects on stained glass windows conservation, and finally at assessing the most appropriate strategy to preserve stained glass windows. Scientific results showed that the so-called isothermal glazing (i.e. ventilation by the air coming from the inside of the building) protected efficiently the ancient stained glass window from environmental attack (i.e. rain, pollutants, condensation, thermal shocks) with very limited secondary effects. The scientific research highlighted that its efficiency was strongly related to the technical design of the protective system. In particular, the ventilation and the size of the interspace had to be carefully considered. The research developed within the VIDRIO project was turned into general recommendations to the owners and practitioners on the best practice for the stained glass windows future conservation.     

A methodology for the identification of glass panes of different origin in a single stained glass window: Application on two 13th century windows

The chemical composition of 11 glass panes originating from two 13th century non-figurative windows were analyzed by means of Scanning Electron Microscopy–Energy Dispersive X-ray system (SEM-EDX). The windows were discovered in the back-wall of the triforium during the restoration of the choir of the cathedral St. Michael and St. Gudule in Brussels (Belgium). In order to determine if these windows were fabricated with glass of different origin or not, the compositional difference between the panes were compared with the variation in composition as a result of the following causes: (1) compositional fluctuation between panes cut from the same sheet of glass, (2) compositional fluctuation caused when panes are cut from different sheets that were made with the same batch, (3) compositional fluctuation caused when the glass is made from different batches at the same production center, and (4) compositional fluctuation as a result of glass produced at different fabrication centers.     

Diagnostic investigations and statistical validation of EDXRF mapping of the burial monument of Pope Sixtus IV by Antonio Pollaiolo (1493) in the Vatican

It has become a common practice to include diagnostics and archaeometric studies during a masterpiece restoration. The advantages and limits of this approach are now topic of discussion in the community of researchers that is growing up quickly. The bronze burial monument of Pope Sixtus IV (1471–84) by Antonio del Pollaiolo, now in the Treasure Museum in the Vatican was intended to be located at the center of a chapel, this explains its apparent asymmetry: lack of height and large base. The restoration of the burial monument started in May 2007, it was carried out by first fulfilling a series of non-invasive analyses using a transportable EDXRF to map the composition of the alloy and evaluate the diagnostic capabilities for deterioration processes of the bronze surface. As a consequence of the first non-invasive diagnostic campaign, a second campaign of micro invasive tests was planned and carried out. The samples were analysed with SEM-EDS and XRF techniques. In this article some of the results of the EDXRF tests will be shown together with the procedures set up to maximize the diagnostic information obtained and minimize the need of microsampling from the artefact. The results and the statistical analysis of data show that a straightforward planning of the measurements can give several, sometimes unexpected, results in the definition of the state of conservation of the monument and also from an archaeometric point of view. With a high amount of data, the use of statistical analysis is necessary, for example in our case, the analysis of the variance confirmed the hypothesis of the use of different alloys for the elements of the panels.     

Assessment of the state of conservation of stone artworks after laser cleaning: comparison with conventional cleaning results on a two-decade follow up

The utilization of laser light to produce fine and selective cleaning of superficial deposits and encrustation from stones was originally proposed more than 20 years ago by John Asmus who performed pioneering trials of laser cleaning on stone façades in Venice, Cremona and Padua. The opportunity to collect stone samples from these sites allowed us to carry out an original study aimed at evaluating the conservation state of stone surfaces cleaned 10–20 years ago by means of three different techniques: Nd:YAG laser radiation, micron sandblasting and chemical pads. Samples of various stone types, as Istria limestone, Botticino limestone and Nanto sandstone were collected and examined by means of optical and SEM microscopy, FT/IR, and EDAX analyses. The results provided preliminary indications that the state of conservation of stone surfaces previously subjected to laser cleaning is generally better in comparison with those which concurrently underwent mechanical and chemical cleaning.     

Creativity at work: the production of work for sale by brand ambassadors

Creative work has emerged at the core of the new economy and is primarily studied in the art and the media, music and advertising business. This article presents data from an ethnographic research with professional rock climbers. It argues that the production of work for sale by these climbers is a form of creative work. The thread of the argument is twofold. First, their work is inextricably intertwined and paced with highly creative activities. Second, it is anchored in a complex system of communication aiming for the production and dissemination of experiences through media production.     

Alternatives to review by peers: A contribution to the theory of scientific choice

Conclusion The questions of scientific choice which were left unresolved when the rapid expansion of academic science in the United States began in the early 1960s have come back to trouble the scientific community. There is now widespread dissatisfaction with the process of review by peers as one of the major systems for the allocation of public funds for research. While earlier criticisms had been brushed off by the assertion—unsupported by facts—that no other systems existed, the present situation cannot be so easily dismissed.A serious examination of other national and international arrangements shows that a wide variety of procedures are in use and there is no research which shows that one system is either more productive scientifically, or more cost-effective in bringing about valuable scientific research. New systems which may be considered should avoid the major defects of the system of peer review as now practised: the enormous waste of scientists' time, the great potential for conflicts of interest, and the inherent bias against innovation.The principal system which I have proposed here combines the best elements of peer review with the simplicity and efficiency of the use of a formula. Moreover, this formula based on peer review of performance incorporates all the elements for which the academic scientific establishment should be accountable to its patron, which is the public treasury. A final virtue of the proposed system is that it provides simple and convenient procedures through the use of numerical weighting factors for the policy-maker to guide the support of scientific research as a whole.     

《不平鸣稿》所见明末徽州的民间纠纷及其解决

中国传统法律的“文本意义”与“实践价值”历来相去甚远 ,而传统法律文化研究中的“大一统”色彩 ,遮蔽了不同地理历史条件下生成的独特的地域文化。明清时期的徽州地域环境中形成和发展起来的徽州地域法律文化对解构中国传统法律文化具有标本价值。本文以记载明末天启、崇祯年间潘余两姓的一桩官司文书———《不平鸣稿》为中心 ,辑录了该稿所收文书 ,描述了两姓之间“六年三讼”的大体历程 ,详述了纠纷的缘起和最终解决之道及其双方所体现的诉讼意识 ,并认为 :在明末徽州民间纠纷的解决过程中 ,民间权威人物的影响已经远不如明初 ,乡民之间的互让互谅往往导致纠纷的最终解决 ,并据此对学界关于明清徽州人擅讼、健讼观点提出质疑。