Abstract: The sol-gel process has been found to be successful in applications for the conservation and restoration of stone. However, a well-known drawback of the materials obtained by this process is their tendency to crack during drying inside the pores of the treated stone. In this article, we present an overview of our current research centred on producing crack-free sol-gel materials for consolidating and protecting building stone. A novel synthesis, in which a surfactant acts as a template to make the pore size of the gel network coarser and more uniform, is shown to provide an effective alternative for preventing the cracking of consolidants. We also highlight an alternative pathway, in which we add an organic component to the silica precursor in the presence of the surfactant. The hybrid organic-inorganic gel prepared in our laboratory provides excellent waterproofing to the stones under study.
Abstract: This paper presents a comparative study of the effects of calcium hydroxide based agents on consolidating a lean lime mortar. In the first part, it describes the properties and characteristics of CaLoSiL® – a new stone strengthener based on colloidal suspensions of lime nanoparticles in various solvents. It further summarizes the results of recent tests on the influence of applying nano-agents based on colloidal calcium hydroxide dispersed in ethanol or isopropyl alcohol (CaLoSiL®), and compares them with the effects of lime water and with a traditional barium hydroxide treatment. The tests were carried out on non-standard test specimens fabricated from a lean mortar (1:9) and developed specially for the purpose of testing the relatively low strengthening effects that are typical for lime water consolidation. The comparison presented in this paper is based on the mechanical characteristics of consolidated lime mortar.
Abstract: Superhydrophobic films are produced by a simple and low cost method. Silica (SiO2) nanoparticles are dispersed in solutions of Rhodorsil 224, a commercial poly(alkyl siloxane) which is used for the protection of outdoor cultural heritage objects, and the suspensions are sprayed on glass surfaces. It is shown that the siloxane-nanoparticle composite films prepared from dispersions of high particle concentrations (≥ 0.5% w/v) exhibit superydrophobic properties (high static contact angle and small hysteresis) which can be rationalized by the Cassie-Baxter model, according to quantitative measurements obtained by SEM images. Siloxane-nanoparticle films are then deposited (sprayed) on “Opuka”, a fine-grained argillite which was used for the restoration of the castle of Prague. It is shown that the treated stone surfaces exhibit superydrophobic properties, similar to the treated glass surfaces. The efficacy of the superhydrophobic films to protect Opuka is evaluated by performing water contact angle, water capillary absorption, water vapor permeability and colorimetric measurements. It is shown that the use of nanoparticles in the protective coating has a positive effect on the results of the aforementioned tests, except for the colorimetric measurements.
Abstract: Lime mortars have been commonly used in historical buildings since ancient times. The progressive deterioration of these mortars by air pollution and other environmental causes hinders the assessment of the original composition. The weakening of the mortar structure is due to dissolution and formation of calcium sulphate layers because of the interaction with SOx gaseous pollutants. Also, pollution particles can be incorporated to the mortar because of dissolution by rainwater or runoff. Scanning Electron Microscopy (SEM) studies allow us to distinguish allochthonous and autochthonous micro- and nanoparticles in order to identify original intact plasters. By comparing these intact to deteriorated mortars from both air polluted and non-polluted areas it is possible to indentify and preserve the original mortar composition as a key step to project future façade cleaning and restorations.
Abstract: This article reviews laser-based analytical techniques, which find applications in the field of cultural heritage diagnostics, providing information about the chemical composition of materials, at the atomic or molecular level. Lasers are intense sources of light featuring unique characteristics that have been exploited in order to enhance the performance of certain spectroscopic techniques such as Raman or fluorescence spectroscopy, or even produce new schemes of analysis, including, for instance, non-linear or remote sensing spectroscopy as well as laser ablative sampling and excitation. In parallel, with advances in laser and detector technology, compact, mobile instrumentation is becoming available that permits broader use of such laser-based techniques for analysis of materials in works of art and archaeological findings.
Abstract: In the last decades, numerous analytical techniques have been extensively used for the compositional analysis of objects of archaeological interest. However, on cultural heritage objects, the application of most techniques, such as AAS, XRD, ICP-MS, NAA and SEM-EDX is destructive and a significant amount of the sample is consumed. Furthermore, many of those techniques are expensive and time-demanding, mainly due to the sample preparation. In this work, LIBS is applied as an alternative technique for the qualitative and quantitative elemental analysis of the black glaze and the main body of an ancient Attic black ceramic. LIBS seems to be a most promising technique for such applications, considering that no sample preparation is required and that it is practically non-destructive, since only few μg of the sample’s surface are ablated. Furthermore, it is flexible concerning the geometrical characteristics of the sample under study and it can be applied in situ, at open field, providing a rapid, user-friendly analytical tool. The study showed that both black glaze and main body of the ceramic consist of the same elements: Si, Al, Fe, Ca, K, Mg, Ti and Na. This indicates that the black glaze is not a decorative paint, but originates from the same clay used for the main body after being processed differently. For the quantitative analysis, calibration curves of Fe, Ca, K, Mg, Al and Ti were constructed, by preparing stoichiometric reference samples of each element in a SiO2 matrix. All the calibration curves are presented and the restrictions for determining each element are discussed. For comparison purposes, the ceramic artifact was also studied by other techniques such as AAS, XRF, SEM-EDX and XRD. The results were correlated with the LIBS data, while the advantages as well as the limitations of each technique for the study of cultural heritage ceramics are discussed. To the best of our knowledge, this is the first complete work to determine quantitatively the compositional differences between the black glaze and the main body of an Attic black ceramic using the LIBS technique and also to compare the LIBS data with the results of other analytical techniques.
Abstract: Particle Proton–Induced X-Ray Emission (PIXE) is one of the most sensitive analytical methods which can be used in the study of ancient mural paintings - especially pigments. It requires small samples or tiny fragments of the paint layer. It is a non-destructive technique and provides data on elemental concentrations. Analysis can be performed in vacuum or in air. The major advantage of this technique is the ability to analyze simultaneously both elements and trace elements present in the sample. Another advantage is the short data acquisition time. This research studies red, yellow, blue and green pigments used in the tomb of Ramesses III (N.11 - 1198 BC), the tomb of Tohthmous III- (N.34 - 1504 BC), both located at the Valley of the Kings Luxor, and also, Medinet Habu temple of Ramesses II (1198 -1166 BC) located at the West Bank of Luxor. The study was performed by using light Optical Microscope (LOM) and Particle Proton–Induced X-Ray Emission (PIXE).
Abstract: Ancient ceramic wall tiles, called “azulejo”, firstly used on Portuguese churches, monasteries and palaces (15-18th century) have progressively been used in particular houses till the last century. These tiles and its use in huge decorative panels can be considered as a precious but fragile cultural heritage from Brazil to India, in several countries influenced by Portuguese culture. Morphologically, these tiles are composed by a porous clay-based ceramic body, the terracotta, covered by a protective glassy phase, the glaze. As artistic paintings, these murals incorporated various kinds of pigments in the glaze layer to create a pictorial impact on the walls of rich palaces or churches, real and durable monumental works-of-art. In the 21st century, degradation marks are visible on these ceramic tiles because of their use under corrosive conditions (moisture, atmospheric cycles…) along centuries. In order to promote their conservation and enhance their restoration, the physical-chemical characterization of the azulejos is performed in the present work, using mainly non-destructive processes like micro-Raman spectroscopy or X-Ray diffraction. In particular, Raman spectroscopy allows the detection of some nano/microcrystals present in the amorphous glaze due to pigments or opacifying agents or related to the elaboration process of the azulejo. Based on the observation of various selected fragments, one states that very few pigments have been used as colouring agents in this ceramic art during 17-18th centuries. Thus, the relationship between the different colours, the introduced pigments and the structural aspects of the glass will be focused. Some features related with the ancient ceramic technology will also be discussed.
Abstract: In this work it has been carried out the diffusion of silver ions in medieval glasses by a heat treatment process. Silver ions are transformed into both silver nanoparticles and nanoclusters after redox reactions with reducing glass ions. Changes in glass colour due to the formation of these silver nanoparticles have been analysed by means of visible spectroscopy. At the same time, changes in glass structure have been analysed by means of Raman scattering. By using confocal Raman spectroscopy the in deep glass structural changes occurring after silver ion diffusion and silver nanoparticle formation have been studied. These changes have been corroborated by means of gradient Raman spectroscopy where the silver ion and silver nanoparticle diffusion have been analysed on a fractured glass surface. In all cases have been observed that silver nanoparticles produce a depolymerisation of the glass structure and that such depolymerisation increases with the amount of silver nanoparticles. By using Microprobe Analysis it has been found that the higher silver nanoparticle concentration is on the glass surface and it decreases with the distance to the surface according to a diffusion process. By using nanoindentation measurements on original and gradient glass surfaces it has been found an increase of the Young modulus from 60 to 85 GPa, being the first value that corresponding to the glass surface with high silver nanoparticle concentration, and the second one for the glass without silver. This result is in accordance with Raman and Microprobe analysis.