Monica Favaro

Evaluation of compatibility and durability of a hydraulic lime-based plaster applied on brick wall masonry of historical buildings affected by rising damp phenomena

Abstract In the framework of the CNR Cultural Property Project for the Safeguard of the Arsenale, it was decided to test some new macroporous plaster designated to resist salt crystallization in order to prevent crystallization phenomena that are damaging the brick wall masonry of Venetian historical buildings. To understand the influence of rising damp and salt crystallisation on the durability of a plaster, in-field experiments were carried out: cores at different heights and different depths were drilled before and after plaster application in order to obtain a vertical and horizontal distribution of moisture and soluble salts. The determination of moisture content was carried out by gravimetric method while the salt content was obtained by ion chromatography measurements of chlorides, nitrates and sulphates. From the first results artificial hydraulic lime-based plaster seems to have a better performance in reducing moisture and chloride content. If this trend is confirmed in the future samplings, as the composition of plaster is the same in both areas, the methodology of application will be the discriminating factor to obtain better performances. Notwithstanding the absence of any damp proof course the state of conservation of the plasters seems to be satisfying. This is probably due to the different position of the evaporation front in the thickness of a macroporous plaster in comparison with a traditional plaster. In fact, in the first case, the evaporation front, and, consequently, the area in which soluble salts are accumulated, is confined to the inner part of the plaster, close to the brick wall, while in a traditional plaster salts are generally scattered throughout the whole thickness, but tend to concentrate mainly near the external surface. Due to this behaviour the traditional hydraulic lime-based plaster shows a superficial exfoliation caused by the crystallisation of soluble salts in the sub-surface; on the contrary, in our case, the artificial hydraulic lime-based plaster does not show either presence of efflorescence or of crypto-florescence.

Characterization of lapis lazuli and corresponding purified pigments for a provenance study of ultramarine pigments used in works of art.

AbstractIn this paper, we propose an analytical methodology for attributing provenance to natural lapis lazuli pigments employed in works of art, and for distinguishing whether they are of natural or synthetic origin. A multitechnique characterization of lazurite and accessory phases in lapis lazuli stones from Afghan, Siberian and Chilean quarries, on the pigments obtained by their purification, and on synthetic ultramarine pigments was performed. According to the results obtained, infrared spectroscopy is not a suitable technique for distinguishing the provenance of lapis lazuli, but a particular absorbance band makes it relatively easy to determine whether it is of natural or synthetic origin. On the other hand, EDS elemental composition and XRD patterns show the presence of specific mineral phases associated with specific lapis lazuli sources, and can be used to distinguish the provenance of the stones as well as—albeit to a lesser extent—the corresponding purified blue pigments. In contrast, FEG-SEM observations clearly show different stone textures depending on their provenance, although these distinctive features do not persist in the corresponding pigments. PCA analyses of EDS data allow Afghan lapis lazuli stone to be distinguished from Chilean and Siberian ones, and can distinguish between the pigments resulting from their purification as well as synthetic blue ones. Although this methodology was developed using a limited number of samples, it was tested on lapis lazuli pigments collected from three paintings (from the fourteenth to sixteenth centuries) in order to perform a preliminary validation of the technique, and based on the results, the provenance of the blue pigments employed in those artworks is proposed. Finally, upon analytically monitoring the process of purifying lapis lazuli to obtain the corresponding pigments, it was found that ion-exchange reactions occur between the alkali modifiers of silicate/aluminosilicate phases and free carboxylic acids present in the doughy mixture of natural terpenes and ground stone, namely pastello. These reactions favor (i) the retention of silicate phases in the organic mixture and (ii) the selective extraction of lazurite due to the formation of Brønsted acidic sites [Al(OH)Si], which are responsible for its high hydrophilicity in comparison to the one of the other species present in the lapis lazuli stone. FigureBack scattered electron image of a polished section of Chilean lapis lazuli rock

New calcium alkoxides for consolidation of carbonate rocks. Influence of precursors' characteristics on morphology, crystalline phase and consolidation effects

New ambient temperature liquid calcium alkoxides, [Ca(O(CH2CH2O)3CH3)2] (1) and [Ca(O(CH2CH2O)3CH2CH3)2] (2), together with [Ca(OCH2C(CH3)3)2] (3), were synthesised by reaction of ammonia-activated calcium with the appropriate alcohol. Their potentiality as stone consolidant products was investigated and compared with those of other alkoxides: [Ca(OCH2CH3)2(CH3CH2OH)4] (4), [Ca(OCH3)2] (5), [{Ca(OCH2CH2OCH3)2}9] (6), already described in the literature. Reaction of 1–3 with the atmosphere was studied, final products analysed and kinetic pathways investigated. The reaction produces CaCO3 and the vaterite/calcite ratios observed in the coatings generated from isopropyl alcohol solutions of 1–6 were found to considerably vary with the alkoxide precursor, which has a strong influence also on the morphology of the produced films. Furthermore, their efficiency as stone consolidants was tested by ultrasound measurements.

Principal decay patterns on Venetian monuments

Abstract In most Venetian monuments studied, the stone decay was ascribed to the transformation of calcium carbonate into calcium sulphate. This phenomenon is commonly observed elsewhere and has been pointed out by many authors. In order to explain why different forms of decay are present on a building facade, samples were taken from different areas of many monuments. Analytical results were related to different forms of decay, defined respectively as white washing, dirt accumulation and dirt wetting. A simplified model of stone decay is presented and its validity tested on several Venetian monuments. Results showed that the features visible on stone surfaces corresponded to different degrees of deterioration. Sulphate formation is greatest in the black dendrite-shaped crusts, which are generally formed at the interface between the white washing areas and the sheltered ones, which were defined as dirt wetting area. The decay forms of the most common lithotypes used in Venetian monuments were also studied. Results obtained showed that in compact limestone, gypsum formation affects the stone only on the surface. In contrast, on marble a different mechanism of decay takes place: the decohesion of calcite crystals, due to thermal changes, favours the penetration of sulphuric acid solution into intergranular spaces, thus causing the transformation of calcium carbonate into calcium sulphate, not only on the surface, but also inside the marble.

Innovative consolidating products for stone materials: field exposure tests as a valid approach for assessing durability

The impact of climate on cultural heritage surfaces leads to several damage processes and the protection and the preservation of works of art is a challenge for conservation scientists and restorers. Traditional and innovative products are used in consolidating treatments in order to reduce the effects of the interaction environment-materials. The EC NANOMATCH Project aims at the development of innovative consolidating agents for carbonate matrices, wood and glass whose features should result in high compatibility, efficiency and long-lasting effect. In this project, metal alkoxides, molecular precursors for the deposition of metal carbonate are synthesized, characterized, tested and proposed as an alternative to traditional consolidating agents as well as to calcium hydroxide nanoparticles. This paper gives an overall description of the methodological approach adopted for the in field evaluation of durability taking into account the environmental impact. Preliminary results of the analyses carried out on carbonate stones aimed at investigating the features of the consolidating treatment are here presented and discussed.

Calcium and Magnesium Alkoxides for Conservation Treatment of Stone and Wood in Built Heritage

In the frame of the EU-project NANOMATCH new consolidants based on metal alkoxides were developed and tested. New compounds were prepared with different synthetic pathways to overcome the oligomerization issue, which can strongly influence solubility and therefore application of alkoxides as conservation materials for built heritage. Calcium alkoxides react in presence of humidity and carbon dioxide to give CaCO3 and alcohols. This peculiar behavior -in atmospheric conditions- makes this class of chemicals suitable for consolidation of carbonate stones, plasters and wall paintings and also for pH buffer to avoid acidification of cellulose based materials such as wood and paper. Within the frame of the project, it has been demonstrated that the developed calcium compounds are more soluble than the corresponding commercial Ca-bearing consolidants and, after reaction with air, they evolve into different calcium carbonate structures, i.e. amorphous carbonate or crystalline calcite and vaterite. The ratio among these forms can be oriented by environmental conditions and treatment with water, in order to force a carbonate phase in place of other ones. Commercially available magnesium alkoxides solutions were also tested as consolidants precursors. Carbonation of magnesium compounds brought to precipitation of low crystalline Mg hydroxide and carbonate coatings. Moreover, hydrated Mg carbonate phases were identified. Many of them are salts sensitive to water and prone to ion-exchange, possibly evolving to soluble magnesium salts deleterious for stone. These experimental evidences led to the decision to discard magnesium alkoxides for conservation purposes.

Electron Backscatter Diffraction in Conservation Science: Phase Identification of Pigments in Paint Layers

Electron backscatter diffraction (EBSD) was used in Conservation Science for characterization of ancient materials collected from works of art. The results demonstrate the feasibility of EBSD analysis on heterogeneous matrices as very small samples of paint layers collected from paintings. Two reference pigments were selected from those used by artists to investigate the relationship existing between EBSD pattern quality and properties of the investigated material (i.e., average atomic number, density, and Mohs hardness). The technique was also tested to investigate the pigment phases on two real samples collected from Romaninos Santa Giustina altarpiece, an oil on wood painting dated 1514 (Civic Museum, Padova, Italy). Results show for the first time the acquisition of EBSD patterns from painting samples mounted in resin, i.e., painting cross sections, opening a new powerful tool to elucidate the pigment phases avoiding large sampling on works of arts and to further study the complex mechanisms of pigment deterioration.

Study of challenging calcium alkoxides in solution by electrospray ionisation mass spectrometry (Part 2).

Calcium alkoxides in solution give rise to oligomers with different reactivity and solubility and, as observed in a previous investigation, small differences in the ligand structure lead to strong differences in the cluster composition. Electrospray ionisation mass spectrometry (ESI-MS) gives evidence of this behaviour, allowing the identification of these oligomers. In this paper, ESI was applied in the study of calcium alkoxides with different steric hindrances and with additional donor atoms on the ligands. A systematic analysis was conducted by varying the ESI instrumental parameters (voltages, temperatures) to identify the best conditions for the analysis of this class of compounds. Furthermore, particular attention was paid to the study of the best solvent to be employed, considering the possible occurrence of alcoholysis and decomplexation phenomena.

PANNA project --- plasma and nano for new age soft conservation. development of a full-life protocol for the conservation of cultural heritage

EU PANNA project started on November 2011 and aims at integrating a novel atmospheric plasma technique for surface cleaning and two innovative coating typologies (self-diagnostic protective coatings and identification marker coating) in a full-life protocol spanning surface cleaning, deposition of coatings and their complete removal. The validation of the protocol will be achieved through the cooperation between conservation scientists and technological companies. In the project, the development and testing of the protocol will be performed on two categories of substrates: metals (bronze and silver) and stone and stone-like materials (limestone, sandstone and wall paintings). The development will be performed on laboratory prepared samples (dummy or replica or mock ups) and also on real objects.

Nanomatch: A European Project to Develop Consolidants through the Synthesis of New Inorganic Nanomaterials for the Conservation of Built Heritage

The problem of deterioration of historical building materials, namely stone, wood and glass has become more and more urgent. Climate changes have increased the impact of natural decay whilst socio-economic requirements claim a more sustainable use of existing built heritage. The EU project NANOMATCH addresses this problem through the development of a family of innovative materials. These are specifically designed for the consolidation requirements of historical substrates and for the production of high performance products to fill the gap in the market dedicated to the conservation of built heritage. Metal-alkoxide precursors will be synthesized and their properties will be tuned based on the substrate characteristics of respectively stone, wood, glass to fulfil specific functionalities. The consolidation effects will be first evaluated through lab experimentation and subsequently the most suitable metal alkoxides will be tested in different European sites to evaluate also the environmental effects on their performance This will lead to a new generation of nano-products specifically tailored for historic materials in a context of climate change, emerging from the most recent and advanced research in the fields of conservation science and nanotechnologies. The development of suitable products for the treatment of historical materials will finally stop the inappropriate use of several commercial products, especially polymers. These have shown in recent years detrimental effects due to their fast deterioration and have also hampered the treated material as well. Central to the project is the synthesis of molecular precursors, nano-coating deposition and assessment of their conservation properties leading to the production of innovative products for the market of conservation in replacement of unfit traditional ones. The basis for their production and market introduction will be developed within the project