Consolidation of paint on stained glass windows: Comparative study and new approaches

Stained glass windows belong to the most precious pieces of art in many European countries. Examples of heavily endangered paint on glass are reported in the literature and mainly related to condensation effects and air pollution, as stained glass windows preferably remain in their original architectural surrounding. Several surface coatings and paint treatments have been proposed to consolidate and protect degraded paint. Very often, the selection of the materials is based more on practical aspects than on scientific research. This study concerns the comparison of some traditional, modern and newly developed consolidants for the preservation of historic glass paintings. Experiments have been carried out with model painted glass samples simulating weathering phenomena of originals. Traditional materials like Paraloid B72, modern ones like SZA (proposed by the Fraunhofer-Institut für Silicatforschung, ISC), and three new consolidants prepared by the sol–gel method and based on different hybrid organic–inorganic alkyl-alkoxysilane systems have been considered. The adhesion, penetration, stability, hydrophobicity, mechanical and chemical resistance are properties and requirements tested to prove their effectiveness and range of use. The three new materials developed in this study for the consolidation of paint on glass have the potential to offer alternatives to existing materials. Nevertheless, further research is necessary before their application in restoration workshops can be recommended. A strategic approach is requested to avoid risks for these valuable historical originals and to contribute to the long-term preservation of the paint on stained glass windows in their original sites.     

Analysis of calcium acetate efflorescences formed on ceramic tiles in a museum environment

Salt crystallization is a major cause of damage in porous materials such as stone, brick and ceramics. The paper reports results of an analytical study on tiles of glazed ceramics that are seriously damaged by acetate salt crystallization. Measurements of the ionic composition of the salt mixture in the tiles and in the efflorescences were carried out. Based on the available information on the phase equilibria in the system comprising of the main constituents chloride, nitrate, acetate, calcium and sodium, the crystallization pathways of the various solid phases are traced. It is shown that a combination of qualitative XRD analysis of the phases present in the efflorescences together with a quantitative determination of the ionic composition is sufficient for the quantitative analysis of major crystalline species in the efflorescences, i.e. Ca₃(CH₃COO)₃Cl(NO₃)₂ · 7H₂O, thecotrichite, and NaCl, halite. The concentrations of these salts are obtained from a solution of the mass balance by least squares analysis. Their formation from the salt mixtures present in the tiles that are subject to acetic acid vapor attack is consistent with the solubility diagram of the above mentioned quinary system. Finally, the possibilities of preventive conservation of salt contaminated ceramics in typical museum environments are discussed.     

Acrylic copolymer coatings for protection against UV rays

This paper summarizes the basic properties of new acrylic copolymers with UV-absorbing groups (derivates of benzotriazole) bonded in macromolecular chains. These polymers are highly suitable as a material for UV protective coating of artifacts sensitive to natural and/or artificial UV light. Diane type epoxy resin was used as a test organic material with very low resistance to UV radiation. The behavior of new copolymers was compared with the UV protecting ability of Paraloid B72. Based on obtained results, we have chosen the copolymer whose properties were most similar to those of Paraloid B72, but whose protective ability is superior. This copolymer is now commercially available.     

Evaluation of the effectiveness of treatment products in improving the quality of ceramics used in new and historical buildings

Ceramic samples made with a mixture of 70% ball clay and 30% quartz sand were moulded and then fired at 900 °C in an electric kiln. Samples were then treated with different products and analyses and tests were performed to evaluate the physical changes induced by the application of these products and their effects on the quality of the ceramics. A petrographic study indicated that the ceramics were composed of quartz, small amounts of mullite and sanidine and traces of hematite. Mineral clays (i.e. kaolinite) disappeared during firing. Two consolidating products (Paraloid B72 and Tegovakon V) and one water repellent (Silo 111) were applied to samples by capillarity, and physical changes (colour, water flow, porosity and pore size distribution) were measured. Finally, we carried out salt crystallization tests in order to determine which product improved the quality of the ceramics. Treated samples registered a decrease in porosity and a general increase in pore size. The application of Silo 111 drastically reduced water absorption by immersion and by capillarity. This product was also responsible for a decrease in pore interconnection. Samples treated with Tegovakon V performed better in terms of their overall hydric behaviour. Silo 111 was the only product that did not modify the colour of samples when compared with untreated ones, and after accelerated aging tests, samples treated with this product hindered the absorption of saline solution into ceramic pores and prevented their decay. Paraloid B72 did not improve any of the properties of the ceramics.     

Manufacturing expedients in medieval ceramics in Apulia

A group of 51 shards of medieval polychrome glazed pottery, coming from Canosa castle archaeological site (Bari, Italy), has been investigated through surface analytical techniques, such as Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) and elemental ones, such as Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) and Absorption Atomic Spectroscopy (AAS) by flame and electro-thermal atomisation. The investigation was aimed at defining the elemental composition of pottery findings, identifying pigments and clarifying glaze types. The results of the analytical characterization allowed the identification of materials and technological expedients used for pottery manufacturing, highlighting original features in the production of the investigated pottery.The quantitative analysis performed on ceramic paste, glaze and painted decorations provided a significant number of results, thus enabling their effective exploitation for multivariate statistical techniques, in order to find out possible groups of pottery items with defined similarity within the samples.     

Tailoring new fluorinated acrylic copolymers as protective coatings for marble

The protective performances of two new fluorinated acrylic copolymers (based on the monomers 1H,1H,2H,2H-perfluorodecyl methacrylate (XFDM) and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFIM) are evaluated and compared with Paraloid B72, a commercial copolymer ethyl methacrylate/methyl acrylate (EM/MA) and its partially fluorinated homologous 2,2,2-trifluoroethyl methacrylate/MA (TFEM/MA). The polymeric materials have been tested on Candoglia marble, a very low open porosity stone (<1%) used in Italian historical architecture (Milan Cathedral). The copolymers were tested according to UNI-Normal protocol. Measurements of capillary water absorption, static contact angles, colour variation and water vapour permeability were made before and after accelerated photo-ageing. FTIR spectroscopy and size exclusion chromatography (SEC) analyses were carried out on samples aged on inert substrate to assess the photostability of the copolymers themselves. The relationship between the protection efficacy and the fluorine content and distribution has been investigated. The results obtained show that the addition of a partially fluorinated co-monomer to the Paraloid B72 copolymer structure did not result in the expected improvement of the coating properties, while the fluorination of the copolymer side chain gave rise to encouraging performance.     

Characterization of 17th Century Mughal tile glazes from Shahdara Complex,Lahore-Pakistan

The glazed tile decorative art was one of the widely used ornamental techniques for the monumental buildings during the Mughal period, in Pakistan. Coloured tile samples from Jahangir tomb were analyzed to know the glaze composition and to identify the colouring phases used at that time. The study was performed using light microscopy (OM), scanning electron microscopy equipped with energy dispersive X-ray analyzer (SEM-EDS), Raman spectroscopy (RS) and electron microprobe analysis (EMPA). These complementary analytical techniques allowed characterizing the samples as alkali glazes made from plant ashes. The results indicated the use of lead-tin yellow type II for yellow glazes, cobalt and copper for blue glazes, mixtures of yellow and blue glazes for the green glazes, manganese for purple glazes, and a transparent glaze layer for white glazes.     

Methyl–modified hybrid organic-inorganic coatings for the conservation of copper

A simple sol-gel technique for the preparation of methyl–modified silica coatings for the protection of the external surface of copper has been used in this study. Tetraethylorthosilicate (TEOS) has been used as a precursor to prepare nanosilica coatings on the surface of copper. The methyl–modified silica sols were obtained by mixing of 3% SiO₂ sol solution with trimethylchlorosilane (TMCS) or hexamethyldisilozane (HMDS) as basic materials. For comparison, the copper substrates were also coated with commercial polymers (Paraloid B 72, Plexisol P 550-40 and polyvinyl butyral (PVB)). The surface morphology changes of uncoated and coated specimens were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The hydrophobicity of surfaces and photochemical ageing effects were evaluated by contact angle measurements. Potentiodynamic measurements were obtained in order to compare corrosion parameters of the coatings.     

Consolidating properties of Regalrez 1126 and Paraloid B72 applied to wood

This study is aimed at an assessment of the properties of two polymeric products applied to Norway spruce (Picea abies) and White poplar (Populus alba) wood species. It contributes to ongoing research experiments on the consolidating properties of two synthetic resins and their potential synergic action on wood, resulting from their different interaction with the substrate: Paraloid B72 and Regalrez 1126. Experiments were carried out on a series of samples of the two wood varieties. The consolidants were applied alone and one after the other, with one coat of Regalrez and then one of Paraloid. Porosity and variations in pore size distribution were ascertained by mercury intrusion porosimetry (MIP). Colorimetric and IR spectroscopic measurements were also taken before and after aging by solar radiation and freeze/thaw cycles, to verify the possible slowing of photodegradation of the treated wood and the consolidating resistance. Results confirm that both products penetrate the wood with a different behaviour. After double treatment with Regalrez + Paraloid, a significant advantage was observed in terms of mechanical resistance and pore size distribution, although no advantages as regards resistance to photo-oxidizing processes or colour changes were observed.     

Desalination characteristics for ceramics excavated from Taean shipwreck,Korea

The ceramic artefacts, excavated from ancient shipwrecks, are generally saturated with soluble salts, mainly NaCl, within the porous structure of ceramics. The salinity contents typically exhibit ionic and osmotic pressures to the ceramic microstructures, thus causing significant damages to the integrity of ceramic artefacts. While the utilisation of aqueous soaking methods is commonly accepted for effective desalination processes of ceramics, the relationships between the structural characteristics of ceramics and the desalination efficiency have not been demonstrated. In this study, we examined the desalination processes of various ceramics excavated from the Taean shipwrecks in South Korea to identify major controlling factors for the desalination processes. Our results indicated that the physical properties of ceramics including the water absorption and the pore size distribution greatly influence on the desalination process time and efficiency. It is also found that the surface condition of ceramic samples such as microstructural cracks on the glaze layer is a crucial component of the desalination characteristics. Nevertheless, the small residue of salts such as NaCl crystals were found in the microstructures of some ceramics after prolonged desalination periods. Therefore, it is important to control the humidity and temperature in the conservation environment for desalinated ceramic artefacts even after desalination.     

Organic-inorganic material for the consolidation of plaster

Organic-inorganic materials to be used as hydrophobic consolidants for plasters were synthesized starting from an inorganic precursor (Tetraethoxysilane [TEOS]), added to a polysiloxane epoxy formulation and thermally cured with Ytterbium as acid catalyst. The TEOS reduces the viscosity of the resin, contributing to the mechanical properties of the film, without causing cracking. Solvents, that are harmful for workers and environment and show some drawbacks in the practice of restoration, were not used. The film properties and the formation of silica clusters were investigated. The products were applied by brush on plaster's samples and their compatibility and effectiveness were verified. Thanks to the organic content, the products penetrate deeply, are more stable to photo-oxidative degradation, and the hydrophobicity of the resin, provided by the silicone component, is not altered.     

The Basilica of San Vitale in Ravenna: Investigation on the current structural faults and their mid-term evolution

A finite element model was developed to analyze the Basilica of San Vitale in Ravenna (Italy), a Byzantine building which suffers diffused cracking and excessive deformation, mainly as a consequence of complex architectural vicissitudes (extensions, demolitions …) and ground settlements. In the structural analyses, account was taken of permanent loads (self-weight), boundary displacements increasing in time, and seasonal thermal changes. Thanks to previous topographical surveys of part of the building, to chemical and mechanical investigations, the geometry of the Basilica and the main physical properties of the materials are reasonably well defined. The geometric model does not virtually neglect any structural element and accounts for the lack of symmetries in the building. Because of the complexity of the geometric model, a simplified (linearly elastic, isotropic) constitutive law had to be assumed to keep the computing time within reasonable limits. Accordingly, the performed analyses constitute only a first step toward the understanding of the structural behavior of the Basilica, as the adopted constitutive law can only partially explain the surveyed crack pattern, which is influenced by the brittleness and the anisotropy of the constituent materials.     

Microstructure,composition and processing of 15th century Vietnamese porcelains and celadons

Fifteenth century porcelains and celadons are the most interesting ancient Vietnamese ceramics, both from the material and aesthetic points of view. This paper reports on composition, microstructure and technological processing of the Chu Ðâu-My Xa (Hai Duong province) ceramics. Samples come either from the kiln site or from the Cù Lao Chàm (Hôi An) shipwreck. Chemical analysis, scanning electron microscopy, EDX analysis, X-ray diffraction, Raman spectroscopy, thermal expansion/shrinkage and open porosity measurements were systematically performed. The results show the Ca (+K)-based glaze, high-temperature-fired bodies, by one- or multi-step firings. Mullite phase (3Al₂O₃·2SiO₂) was formed in large amount indicating the true porcelain quality of the samples under study. The matrices used for overglaze colouring (e.g., the green, red and metallic-lustre) are lead-based low-firing-temperature glasses. Comparison was made for the structural elements and fluxing agents between the 15th century Vietnamese porcelains and the time-corresponding Chinese ones.     

Deterioration mechanisms of building materials of Jiaohe ruins in China

Almost all defects of earthen buildings such as roughening, erosion, volume reduction, cracking as well as crazing, etc., have been witnessed in the ancient city of Jiaohe, an earthen architectural heritage in northwest China. In this paper, their long-term durability and deterioration due to prolonged exposure to environmental factors were studied, based on the basis of field investigation and laboratory analysis. The results indicated that the deterioration of building materials should be attributed to their basic properties, including density, particle size distribution, soluble salts, mineral, mechanical strength, etc., and interaction with environmental factors. And then, four main deterioration modes can be identified, namely: wind-related deterioration, water-related deterioration, temperature-related deterioration and chemical related deterioration. It can be concluded that the greatest deterioration was wind-related deterioration on west-north facing façades, and chemical related deterioration on the surface of building materials.     

Microfacies analysis and endogenic decay causes of carbonate building stones at the Asklepieion Epidaurus monuments of Peloponnessos,Greece

The carbonate building stones from the Asklepeion, Epidaurus, used to construct the monuments of Gymnasium, Tholos and Avaton can be grouped into 12 microfacies types, according to their microfacies characteristics such as the type of groundmass, the different kinds of particles, the facies-diagnostic fossils, the depositional and solution textures. Two of them, oocalcarenite (MF type I) and biocalcarenite (MF type II) belong to the marine Plio-Pleistocene carbonate sediments from Korinthos (ancient quarries in Kechries) and the northern part of the island of Aegina, respectively. Most of them, calcrete (MF type III), red biomicrites (MF type IV and V), oolitic grainstone (MF type VI), bio-grainstone (MF type VII), boundstone (MF type VIII), intrabreccia limestone (MF type IX), cherty biomicrite (MF type X) belong to the sedimentary carbonate formations of Mesozoic age of the adjacent areas in Argolis peninsula. The black lime-biomicrite (MF type XI) comes from a more distant sedimentary lithological formation, most probably from Dervenakia area (Tripolis zone). Finally, one belongs to the metamorphic carbonates (marbles of Naxos?). The endogenic decay causes are controlled by both sedimentary and diagenetic processes reflected in the microfacies type. So, the main endogenic factors of the oocalcarenite and biocalcarenite facies, which were used for the upper architectural members, are high porosity and the quantitative–qualitative mineralogical composition of the insoluble residue, which is mainly composed of swelling clay minerals (smectites). The calcrete facies, which was used in the foundations of all monuments, shows the heaviest decay problems which are related to the high structural irregularities, the high porosity and the quantitative–qualitative mineralogical composition of the non-carbonate minerals. The other facies appear with a weaker degree of decay whose endogenic causes are also investigated.     

Investigation of the technology of historic mortars

Historical evidence on the use of mortars to meet several needs has existed for millennia. With reference to the characteristic historical periods of the city of Rhodes, mortar sampling was performed on historical constructions, masonry and architectural surfaces. In the present work the different mortar technologies are investigated aiming to answer questions regarding their finality, i.e. whether their differences arise mainly from the various historical periods of construction or from the purposes they had to serve, imparting to the mortars the properties required by their function in the structure. Mineralogical, chemical, physical and mechanical investigations have been performed on characteristic samples after gradation. The exponentially declining function of the ratio CO₂/H₂O structurally bound to the CO₂ content shows a continuous evolution of the kinetics governing the various mechanisms of carbonation of the binder or the formation of hydraulic components during setting, hardening and ageing of the mortars. The grouping of mortars in well-distinct ‘hydraulic levels’ is ascribed to the physico-chemical cohesion and adhesion bonds developed at the matrix and matrix/aggregate interfaces, respectively, allowing for the mortars to either bear continuous stresses and strains as joint mortars or provide compact impermeable renderings which harden even more on contact with water. Hence, parameters determining the diversification of the resulting mortar/matrix types concern the raw materials employed as binding materials and the production processing.     

Transylvanian glass icons: A GC/MS study on the binding media

Transylvanian glass icons are very specific heritage items of Romanian folk art, produced from the middle of 18th century until now. The present research reports the results of a study on the organic components of the paint layers, analyzing the binding media of a series of glass icons belonging to three important icon making centers: Nicula, Olt County (?ara Oltului) and Brasov area (?cheii Bra?ovului). The analysis of the binding media has been done by means of gas chromatography coupled with mass spectrometry (GC/MS). The applied analytical procedure allowed the characterization of the proteinaceous, polysaccharide and lipid-resinous content of the binding media starting from a unique microsample. Results showed that a wide range of materials were used by the icons painters, mostly applied as mixtures of a proteinaceous material and a lipid one. The proteinaceous component proved to be mainly egg, though animal glue and casein were ascertained too, and proteins were often mixed; the lipid material was identified as linseed oil. In some of the icons pine resin and saccharide material were found. Data also highlighted that though the materials used in all the glass icons under study are similar, some particularities could be observed in the painting technique of the studied producing centers and icon painters.     

Recording and documenting the chromatic information of architectural heritage

One essential approach in preserving architectural heritage is the documentation of 3D geometries and surface textures of historic buildings. For example, precise colour information, excluding lighting effects, is an intrinsic property of the surface materials of building interiors and exteriors. However, while colour information has been recorded for small sample areas, it has not been accurately documented on the scale of entire building surfaces. This is critical, because building materials decay and their colours fade with time. The goal of this project is to develop a method to assist in recording and documenting the chromatic information of interiors and exteriors of historic buildings with low cost and high efficiency. The method takes advantage of emerging high dynamic range imaging (HDRI) technology, which can store rich information about colour and illumination through digital photography. By recording the colour information, in addition to the geometry and texture information obtained through other existing technologies, we can achieve more complete documentation for architectural heritage. In this paper, we discuss an overview of the problem and present our algorithms for utilizing computer vision techniques to retrieve chromatic information of historic buildings. We also present and discuss our experiments and results of applying our method to studies of lab objects and the Hall of Supreme Harmony in the Forbidden City, Beijing.     

Rising moisture,salts and electrokinetic effects in ancient masonries: From laboratory testing to on-site monitoring

The investigation of capillary water rise mechanisms in old masonries is of great practical interest, as well as the investigation of the electrical effects accompanying such phenomenon. In fact, moisture presence facilitates all the decay processes in porous building materials and strongly threatens the preservation of materials in architectural heritage. Previous papers have shown that performing a correct and accurate measurement of spontaneous electric potential in masonries is very challenging due to several variables influencing these phenomena, such as materials microstructure, soluble salts nature and amount. In this paper, the influence of mortar joints on the capillary water rise and on the related electrokinetic effects was investigated on laboratory assemblies; then, the same measuring procedure was applied on site to a real XVI Cent. masonry building affected by rising damp.     

Halite – A new calibration material for microdrilling resistance measurements

This paper aims at proposing a new calibration material for microdrilling resistance measurements. Microdrilling resistance is a microdestructive method mainly used in built heritage in order to determine the strength profile in depth. This method is suitable to detect changes in the material cohesion, either due to a different state of preservation or to the action of a consolidant. Calibration materials are often used in microdrilling measurements in order to characterise the drill bit initial value and to correct the variations existing within the initial values of a set of drill bits. Calibration materials are also useful to detect the wear effect on a drill bit due to an abrasive stone. Moreover, such materials can be used for comparing results obtained with different microdrilling machines. In this work, halite was chosen to be tested as a calibration material due to its properties, as low hardness and isotropy. Halite single crystals and halite salt stone from different provenances were tested in order to evaluate the suitability of this material to the requests of a calibration material for microdrilling resistance applications, as for instance being homogeneous, non-abrasive, sensitive and available worldwide. Experimental results show that halite from different provenances is very homogeneous, especially in the crystalline form. This form of halite is slightly more expensive than stone halite; however its costs are comparable to ARS and significantly lower than Macor (other calibration materials commonly used for microdrilling resistance measurements). Due to the advantages of halite for calibration purposes, this material should be further tested by other authors in order to validate our conclusions.