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.     

Water dispersed polymers for textile conservation: a molecular, thermal, structural, mechanical and optical characterisation

With the aim of identifying new water dispersed polymers for textile conservation, the structure and properties of three commercial polyacrylates and one commercial polyvinylacetate were analysed. The characteristics of these materials, not previously used in the conservation and restoration fields, were compared with that shown by Primal AC33 and Mowilith DMC2 and SDM5, widely used as consolidating or adhesive agents of ancient textiles. To achieve a thorough characterisation of each polymer, molecular, thermal, structural and mechanical investigation techniques were applied on film samples, obtained from polymer water dispersions through water casting at room temperature and/or compression moulding. The photo-oxidative resistance of these materials was also assessed by artificial weathering of water cast films and by measuring the Yellowing Index (YI) as a function of the exposure time under xenon-arc lamp. Collected data were used to appropriately compare the performances shown by these polymers when applied on artefacts consisting of natural fibres. In particular it was found that, among the products not previously used in the conservation and restoration fields, a high potential for carrying out treatments on textiles is shown by the samples commercialised with the trade names of Acrilem RP6005 and Acrilem 30WA. These products, in fact, exhibit properties that make them suitable as substitutes for Primal AC33 and Mowilith DMC2 and SDM5, respectively, depending upon conservation needs. It was very interesting to note that Acrilem 30WA, also after aging, shows YI values lower than that shown by Mowilith DMC2 and SDM5.     

Micro-Raman spectroscopy for standard and in situ characterisation of painting materials

Micro-Raman is a spectroscopic technique that allows the identification of painting materials even if finely grained and mixed with others, dispersed in a binder or layered on surfaces. It is used for non-destructive, in situ measurements and it is suitable for selective studies on inhomogeneous materials or surface investigations. Some examples are described of the use of this technique in the field of art conservation and diagnostics, with regard to pigments, dyes and some products of metal alteration. Raman spectra obtained on standard painting materials were arranged in a database and published on the Web.     

What do plastics emit? HS-SPME-GC/MS analyses of new standard plastics and plastic objects in museum collections

In recent years, plastics are designated as a source of indoor pollution and particular attention has thus been devoted to the identification of emitting low molecular weight compounds. Headspace-solid phase microextraction-gas chromatography coupled with mass spectrometry (HS-SPME-GC/MS) has been already successfully applied for screening emissions from synthetic materials. This analytical tool being also non-invasive, it has been already successfully applied in the field of cultural heritage science for the identification of volatile organic compounds (VOCs) emitted from various museum objects made of natural materials. In this research, we aimed at assessing the use of HS-SPME-GC/MS as an in situ non-invasive analytical tool for a better knowledge of the volatile organic compounds emitted by plastics in collections. The possibility of characterizing plastics based on their emission signatures was also evaluated. Twelve new standard plastic samples, belonging to seven main polymer families widely present in museum collections as well as three naturally aged museum objects, were investigated. In this paper, we provide a survey of the VOCs emitted, and the use of HS-SPME-GC/MS for identifying volatile marker compounds, degradation products, additives, and monomer residues of the plastic synthesis is evaluated. More than 200 different VOCs were identified from the new standard samples. Two categories of VOCs were distinguished: “non-specific” and “specific” ones. We showed that based on the “specific” VOCs, it was possible to identify the nature of the polymeric matrix itself or at least to unambiguously distinguish a plastic by family. Emissions from the museum objects were then characterised, and main volatile degradation compounds considered as degradation markers of the natural deterioration of polymeric matrices, were identified. This identification procedure could be further exploited for the characterization of VOCs emitted by objects made of multiple synthetic polymers. Complementary to other techniques, this analytical tool is an interesting way to assess the risk for the objects stored in the vicinity of emitting plastics.     

Durability of the artificial calcium oxalate protective on two Florentine monuments

The use of the artificial calcium oxalate treatment providing a protective patina to marble sculptures and a mural façade has been investigated. The longevity of the protective method is controlled at a distance of 3–4 years from its application on two diversely externally exposed Florentine monuments. Micro samples were analysed by optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX) and MicroRaman spectroscopy to characterize products of deterioration and the efficacy of the applied treatment.Decay is predominately noted at a superficial level and in all cases the calcium oxalate is still present, thus the protective action of the treatment is confirmed and moreover, a consolidant effect is also considered. Both statues present fractures and cavities filled with calcium oxalate residues and various degradation products such as gypsum, lichens and pollution particles. This study contributes to ascertain that artificial calcium oxalate prevents further decay of carbonate materials in urban polluted environments.     

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.     

Definition of the procedure to determine the suitability and durability of an anti-graffiti product for application on cultural heritage porous materials

Anti-graffiti protection is becoming a common practice in many urban buildings, especially in areas of social decay. When Cultural Heritage objects are affected by graffiti, the application of anti-graffiti products can result not only in an unsatisfactory result but also in an irreversible damage of an invaluable cost. The materials commonly found in these constructions are very frequently porous and present different types of decay forms. For this reason, the protection of these materials should be carefully considered. This paper proposes a criterion to decide on the suitability and durability of an anti-graffiti product prior to its application in a porous surface of a protected building. Performance classifications are defined for a series of properties including colour and gloss, and hydric and durability properties, and minimum acceptable values or reductions in these properties are recommended.     

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 case study of an Italian contemporary art object: Materials and state of conservation of the painting “Ragazzo seduto” by Remo Brindisi

This paper deals with the scientific survey of Remo Brindisi's painting “Ragazzo seduto” (Seated boy), made at the end of the 1950s, that is a symbolic figure of both his personal artistic solitude and the crisis of values determined by the economic boom in the post-war period. In a period of great changes and economic regrowth, the need to find a new style that could be the most authentic and personal as possible pressed the artist to experiment innovative products, including non-conventional support. Photographic and analytical techniques demonstrated the use of innovative products as an experimentation tendency, that pressed the artist to use non-conventional support, industrially treated with plasticized PVC and primed with acrylate polymers and to paint with traditional and industrial pigments mixed with an oil-modified alkyd resin. In the span of a few years, an unexpected and extended degradation on the whole surface of the painting took place, with the consequent formation of lifting and detachment of the paint film. The detected alteration is mainly due to the fast ageing of the employed polymeric materials, actually responsible of the impermanence of many contemporary works of arts. Clarifying the unknown aspects of the Remo Brindisi's stylistic choices together with the deterioration processes of the employed painting materials, this paper highlights the general problems related to the conservation of contemporary art, a neglected area of research in Italy, where more efforts are committed to the enormous and more ancient cultural heritage.     

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.     

Tracing of decay profiles and evaluation of stone treatments by means of microdrilling techniques

The recent development of a new drilling machine in the framework of the EU project HARDROCK brought some interesting perspectives for the characterisation of decay profiles, for tracing old consolidating treatments and for evaluating new consolidants. The equipment executes a drill hole, typically 5 mm in diameter, down to 5 cm, under precisely defined and controlled drilling conditions. The output is a graph of force versus depth. The instrument can be transported and operated in situ. The operator defines the drilling rotation speed and the advancing rate and the instrument registers the force required for executing the hole under those strictly defined conditions. This paper presents some data taken from a laboratory study on consolidants which demonstrate that the equipment has a very high discriminating power for detecting the presence of consolidants. Clear differences among some typical consolidants were detected, both in the strength increase and in the penetration depth. They also show that the average drilling forces present a fairly good correlation with bending strength, in spite of the fact that full consolidation of the tested specimens was not possible with all consolidants. The in situ study of Porta Especiosa has shown that the instrument was able to identify the presence of decay events at several depths, in a way that no other known method can do. The identification of the presence of old treatments was demonstrated with total guarantee.     

Structural investigations and analyses for the conservation of the ‘Arsenale’ of Venice

Systematic interventions are being planned and progressively designed on most buildings of the Arsenale of Venice, the Venetian republic’s shipyard, a very large complex of docks and sheds of peculiar construction characteristics. These renovation interventions are required in view of new uses for the revitalizing of that area, which is currently almost completely neglected. In the paper, after a general presentation of the main properties and of the most relevant deterioration phenomena of the principal parts of the monumental area, the methodology that is being used for the structural diagnosis, for the implementation of guidelines for the future interventions and for the maintenance of the restored conditions are presented. Some preliminary results, given by experimental tests performed both in situ and in laboratory on materials and structural elements, and by FE simulations, are discussed.     

A Bacillus subtilis cell fraction (BCF) inducing calcium carbonate precipitation: Biotechnological perspectives for monumental stone reinforcement

Monumental stone decay is a consequence of the weathering action of physical, chemical and biological factors, which induce a progressive increase in porosity. To cope this degradation, bacterial calcium carbonate mineralization has been proposed as a tool for the conservation of monumental calcareous stones. The advantage of this kind of treatment is to obtain a mineral product similar to the stone substrate, mimicking the natural process responsible for stone formation. In this work, the possibility to induce CaCO₃ mineralization by a bacteria-mediated system in absence of viable cells was investigated and tested on stone. Our results showed that Bacillus subtilis dead cells as wells as its bacterial cell wall fraction (BCF) can act as calcite crystallization nuclei in solution. BCF consolidating capability was further tested in laboratory on slab stones, and in situ on the Angera Church, a valuable 6th century monumental site. New crystals formation was observed inside pores and significant decrease in water absorption (up to 16.7%) in BCF treated samples. A little cohesion increase was observed in the treated area of the Angera Church, showing the potential of this application, even though further improvements are needed.     

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.     

A new family of high viscosity polymeric dispersions for cleaning easel paintings

The procedures for making and applying a new family of high viscosity aqueous polymeric dispersions based on poly(vinyl alcohol)-borax (PVA-borax) matrices are presented. A specific system of this type has been used to remove an oxidized varnish coating from the surface of “Coronation of the Virgin with Saints”, a 15th century egg tempera painting on wood by Neri di Bicci (Florence, 1418–1492). FTIR spectra showed that the oxidized varnish was constituted of highly aged shellac resin. Good cleaning performance was attained when the liquid portion of the dispersion consisted of a mixture of water and acetone. Rheological investigations indicate that the acetone content does not affect the mechanical properties of the polymeric dispersion. Those mechanical properties permit easy removal of the cleaning agent simply by peeling it from the surface by means of a forceps or spatula once it has carried out its cleaning function. Optical microscopic and FTIR investigations show that the cleaning agent is able to remove the oxidized varnish coating from the surface of the Neri di Bicci painting without leaving detectable residues.     

Research on protection of the architectural glazed ceramics in the Palace Museum,Beijing

The main damage of architectural glazed ceramics in the Palace Museum was investigated and the photo resistance, thermal resistance of protective materials as well as the protected performance such as hydrophobicity, freeze-thaw resistance, bending and compressive strength of the polymer-applied ceramics was tested. The results showed the main damage of glazed ceramics was the shedding of glaze layer and the change of environmental water and temperature especially subzero was the main reason for the glaze shedding. The photo-resistant and thermal-resistant of protective materials fluorine resin and the compound materials composed mainly of the fluorine resin were better than Paraloid B72 and the compound materials composed mainly of Paraloid B72. The wrapping method was selected for the protection of glazed ceramics and the hydrophobicity, freeze-thaw resistance, bending and compressive strength of the polymer-applied ceramics were improved, especially protected by fluorine resin and the compound materials composed mainly of the fluorine resin. The optimum polymer could penetrate into the damaged seriously glazed ceramics and play a hydrophobic role in the protection. The report will be useful for the preservation of damaged seriously architectural glazed ceramics.     

Medieval and renaissance glass technology in Valdelsa (Florence). Part 1: raw materials, sands and non-vitreous finds

A significant number of archaeological finds of the 13th–16th century from the Tuscan sites of Germagnana and Gambassi in Valdelsa—FI, was studied by different physico-chemical investigations (SEM–EDS, ICP, Mössbauer spectroscopy, XRD, XRF, TG-DTA) in order to contribute to clarify the production methodology and the pre-industrial glass manufacture technology. The studied samples are mainly non-vitreous finds as production waste, refractory materials, crucibles and raw materials; also vitreous finds as frits, skims, glasses (glass masses, glass working waste and finished products) have been taken into consideration. The obtained petrographic and physico-chemical data strongly suggest that both Gambassi and Germagnana glass manufactures were strictly connected with the sources of vitrifiable materials, situated in Tuscan sand quarries. In particular a comparison between sands from the neighbouring quarries and appropriate finds of the two archaeological sites evidences that the employed vitrifiable materials possibly belong to La Casina La Cava resort. The archaeological classification, based on macroscopic observation and stratigraphic position, was compared and verified with the scientific classification of the examined finds of Germagnana and Gambassi sites based on their composition, morphology and physico-chemical properties.     

Aging and yellowing of triterpenoid resin varnishes – Influence of aging conditions and resin composition

The aging of natural triterpenoid resins used as varnishes on paintings is still insufficiently understood. Although progress has been made, questions concerning the aging pathways in light vs. darkness, or the correlation of oxidation with yellowing, remain open. The influence of aging conditions, primarily the amount of light, but also resin composition, on the aging process were investigated. The aging reactions are followed using a variety of mass spectrometric and spectroscopic techniques. Aging processes in dammar and mastic varnishes are shown to be more dynamic and extensive than had generally been believed. In unaged bulk resins, large quantities of radicals develop within weeks after application as a varnish, due to the greatly increased surface-to-volume ratio. This is true for all aging conditions, including aging in darkness, and is accompanied by considerable oxidation as well. After a few months, most of the initial triterpenoids are oxidized. Natural aging in light and darkness leads to the same main aging products. All these findings point to the conclusion that aging largely proceeds by the same pathways in both light and darkness, mainly autoxidation. Without light, enough radicals are formed to maintain extensive autoxidation, although more slowly. Thus, differences between light and dark aging mechanisms are much smaller than often believed. In mastic, the absence of the polymeric constituents is found to enhance oxidation, but reduce yellowing. It appears that the polymer acts as a natural radical stabilizer, favoring the pronounced intrinsic yellowing tendency of mastic. The manipulation of resin composition might lead to improved aging properties of triterpenoid resin varnishes.     

The conservation of the Vecchietta's wall paintings in the Old Sacristy of Santa Maria della Scala in Siena: The use of nanotechnological cleaning agents

In the present article we report a study on some sodium dodecyl sulphate/propylene carbonate based aqueous micellar solutions developed with the aim of setting up a nanotechnological cleaning system to remove naturally aged polymeric acrylic layers from the surface of the wall paintings in the Old Sacristy of Santa Maria della Scala in Siena (15th century). Being these systems mainly composed of water (more than 70% by weight), the cleaning of the painted surface have been performed with low environmental impact, due to the small amount of the pure organic solvents used (always less than 25% by weight). Furthermore, the aqueous phase constitutes a hydrophilic barrier to the penetration of the hydrophobic acrylic materials into the porous support. Fourier Transform InfraRed spectroscopy (FTIR), Scanning Electron Microscopy coupled with Energy Dispersive X-rays analysis (SEM/EDX) and in situ capillary water adsorption measurements indicated the efficacy of this cleaning procedure. Finally, the chemical diagnostics investigation enabled to ascertain the presence of both salts (nitrates and gypsum) and the acrylic polymeric material.