A follow-up on the analytical study of discolouration of the marble statues of Orsanmichele in Florence
Environmental Science and Pollution Research, 2016
The research complements the complex study carried out to understand the source of brown discolou... more The research complements the complex study carried out to understand the source of brown discolourations of ten marble statues in the Church of Orsanmichele in Florence, Italy. Originally located in exterior niches, the statues were restored to reverse the extensive alterations they had undergone throughout the centuries. One of the major alterations was the application of a dark brown patina that dated just after 1789. After the statues were placed indoors, brownish discolourations started to appear on their surfaces. Cross sections were examined using FTIR mapping and immunological methods. In parallel, the pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) data already obtained from the statues' scrapings were compared with data from aged casein films applied to microscope glass slides and aged milk-treated marble. All the statues had been treated with milk-based substances before the time the bronze patina was applied. The values of temperature and illumination of the room were important factors in the ageing of organic substances and in the formation of calcium oxalates. It is likely that products of thermo-oxidation and photo-oxidation of the oils together with the oxalates caused the darkening. The marble samples corresponded to a Lunense provenance.
Immunochemical Micro Imaging Analyses for the Detection of Proteins in Artworks
Topics in Current Chemistry, 2016
The present review is aimed at reporting on the most advanced and recent applications of immunoch... more The present review is aimed at reporting on the most advanced and recent applications of immunochemical imaging techniques for the localization of proteins within complex and multilayered paint stratigraphies. Indeed, a paint sample is usually constituted by the superimposition of different layers whose characterization is fundamental in the evaluation of the state of conservation and for addressing proper restoration interventions. Immunochemical methods, which are based on the high selectivity of antigen-antibody reactions, were proposed some years ago in the field of cultural heritage. In addition to enzyme-linked immunosorbent assays for protein identification, immunochemical imaging methods have also been explored in the last decades, thanks to the possibility to localize the target analytes, thus increasing the amount of information obtained and thereby reducing the number of samples and/or analyses needed for a comprehensive characterization of the sample. In this review, chemiluminescent, spectroscopic and electrochemical imaging detection methods are discussed to illustrate potentialities and limits of advanced immunochemical imaging systems for the analysis of paint cross-sections.
Scientific examination of mural paintings of the Koguryo Tombs
Within the framework of the UNESCO workshops on the Conservation and Preservation of the Koguryo ... more Within the framework of the UNESCO workshops on the Conservation and Preservation of the Koguryo mural paintings which were held in Pyongyang in 2004 and 2005, paint samples were collected from several different tombs (Tokhun-ri, Yaksu-ri, Susan-ri, Jinpa-ri) located in the sub-urban Pyongyang and analyzed by optical, polarized and FTIR microscopy, environmental scanning electron microscopy coupled with energy-dispersive X-ray analysis (ESEM-EDX), X-ray diffraction (XRD), Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC-MS) as well as Raman spectroscopy in order to characterize the composition of pigments, the execution technique adopted and the murals\u2019 state of conservation. The first scientific results seem to suggest the adoption of a \u201cfresco technique\u201d, even though it\u2019s not yet clear whether it was intentionally achieved by painters. To verify this more samples need to be analysed as well as confirmation from an historical literature survey. The external surface of all the paint layers showed the presence of a recrystallized calcite layer, with embedded clayish deposits. Traces of organic materials such as waxes, silicones and natural resins (probably applied during past restoration interventions) have also been detected. The scientific examination results guided the selection of the most appropriate conservation and restoration intervention techniques
CORROSION EvALUATION OF GHIBERTI’S “PORTA DEL PARADISO” IN THREE DISPLAY ENVIRONMENTS
The ‘Porta del Paradiso’ by Lorenzo Ghiberti, also known as the ‘Gates of Paradise’, will soon be... more The ‘Porta del Paradiso’ by Lorenzo Ghiberti, also known as the ‘Gates of Paradise’, will soon be unveiled to the public after undergoing lengthy conservation. This project is at the stage where it is necessary to define environmental criteria for the long-term display of the doors. In this paper, three possible methodologies for display of the doors are considered: a showcase purged with nitrogen; a showcase with low, controlled relative humidity; an open showcase with a controlled microclimate. Galvanic sensors were used inside the cases to continuously monitor the macrocouple current of the doors and establish which case provided the most stable environment for display. Results to date indicate that the showcase with low, controlled humidity may offer the best solution for long-term display of the doors.
Chemiluminescent immunochemical microscope imaging for the identification and localization of casein and ovalbumin proteins in painting layers microsection
This paper presents a study on the influence of ethanolamine (ETH), an anticorrosion agent, on th... more This paper presents a study on the influence of ethanolamine (ETH), an anticorrosion agent, on the polymorphism, morphology, and size distribution of calcium carbonate crystals after room-temperature synthesis. The pH of the solution, the presence of the additive, and the time of crystallization are proved to be important parameters for the morphogenesis of calcium carbonate. Morphologies as diverse as spherulite, rhomobohedral, and scalenohedral micrometric crystals, as well as submicrometric platelike particles, are produced. The mechanism of calcite formation in the presence of ETH involves a mesocrystal transient phase that evolves into classical single crystals. The key parameter of this process is supposed to be the ETH coverage of the primary calcite particles. In particular, it was found that, in particular conditions in the presence of ETH, nanoaggregates of calcium carbonate are formed, which are not stable and, with time, tend to convert into classical rhombohedral crystals of bigger dimensions. This study is relevant for the understanding of basic processes of calcium carbonate precipitation and has a potential applicative impact in the field of restoration when nanomaterials able to penetrate into the porosity of the materials are needed with the aim of reducing the acidity such as on corroded metallic objects or for the deacidification of paper supports.
FT-NIR microscopy: An advanced spectroscopic approach for the characterisation of paint cross-sections
Microchemical Journal, 2014
ABSTRACT The present research was aimed at exploiting and evaluating the potentialities of FT-NIR... more ABSTRACT The present research was aimed at exploiting and evaluating the potentialities of FT-NIR microscopy, as a complementary approach to analysis in the MIR region, for the chemical characterisation of paint cross sections. Even if FT-NIR technique is still underutilised in the field of cultural heritage investigations, the integrated use of information recorded in the NIR and in the MIR regions proved to be extremely useful in the molecular investigation of organic and inorganic substances. In fact, combination and overtone bands present in the NIR region, even if weaker and less selective than those in the MIR region, are not distorted by reflection phenomena. Furthermore, NIR spectra can be efficiently used as a spectral fingerprint for the stratigraphic characterisation of paint cross sections. The proposed analytical protocol was applied on two historical samples, presenting different stratigraphic structures. Suitable chemometric methods were applied for the elaboration of multivariate chemical maps recorded in the range 700–7500 cm− 1. In particular, a comprehensive and efficient procedure based on an interactive brushing approach, which combines the structural information of the score scatter plots with the spatial information of the PC score maps, was used. Interestingly, NIR data allowed a thorough characterisation of paint structures, providing information for the identification of components and suggesting the differentiation among different types of proteins. Moreover, NIR spectra permitted to achieve an efficient distinction of different classes of natural resins, demonstrating that, even working at a microscopic level, the NIR region may support the identification of different terpenoid materials. Multivariate analysis performed on MIR data did not provide satisfactory results, probably due to the distortion of the spectra and overlapping of bands. Nevertheless, MIR outcomes were investigated to support the interpretation of NIR spectra and in attempt to define an integrated protocol for the characterisation of complex paint mixtures.
The analysis of dyes in cultural heritage samples is a well-known challenging task, due to their ... more The analysis of dyes in cultural heritage samples is a well-known challenging task, due to their inherent high tinting strength and consequent low concentration in the carrying matrix a fact that severely limits the number of analytical techniques that can be efficiently and micro-destructively employed for their detection and unambiguous identification. In the present study, an advanced and alternative SEIRA based analytical protocol for the analysis of small quantities of synthetic colorants has been proposed. The method has been set up for the identification of Acid Orange 7 (AO7) using Au nanoparticles obtained by laser ablation in solution (LASiS). Analyses have been performed applying a drop containing a mixture between the colorant and the Au colloidal solution in its unaggregated state on a gold coated glass slide for RAS (Reflection Absorption Spectroscopy) analysis. The first results showed that, thanks to the enhancement produced by the nanoparticles, it is possible to analyze small amount of diluted solutions containing the colorant. Thus, the method has been successfully applied for the analysis of few pieces of dyed wool, after the development of a suitable micro extraction procedure.
The qualitative identification of proteinaceous substances, as well as their location within a co... more The qualitative identification of proteinaceous substances, as well as their location within a complex paint stratigraphy, is one of the most challenging issues in the characterization of painting materials. Nevertheless, information on paint components represent a crucial task for studies concerning both the ancient painting techniques adopted and the state of conservation, being fundamental investigations for the selection of appropriate conservation actions. The present research was aimed at developing a new detection approach for the immunochemical localization of ovalbumin in paint cross-sections based on the use of scanning electrochemical microscopy (SECM). The immunochemical analyses were performed using an anti-ovalbumin primary antibody and a secondary antibody labelled with horseradish peroxidase (HRP). SECM measurements were performed in feedback mode using benzoquinone (BQ)/hydroquinone (H2Q) redox couple. In presence of hydrogen peroxide (H2O2), HRP catalyzes the re-ox...
Macro-attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic imaging is... more Macro-attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic imaging is presented as non-destructive analytical methodology with respect to the sample for the study of paint surfaces. This paper illustrates new opportunities offered by a conventional diamond ATR accessory coupled with a focal plane array detector to obtain chemical images of multi-layered paint cross-sections. The use of a large internal reflection element permits to increase the field of view of the imaging area up to 700 m × 500 m and to obtain FT-IR images of the complete stratigraphy of the sample. This approach represents a versatile analytical tool to determine the composition of the inorganic and organic painting materials and to obtain information on their distribution within the different layers. In the optical arrangement used, a spatial resolution of approximately 15 m is achieved without the use of infrared microscope. This study demonstrates the possibilities offered by macro-ATR-FT-IR imaging for a simple identification of the different compounds present in paint cross-sections before performing further molecular and elemental analyses which may be time consuming or require particular sample preparation.
Alternative SERRS probes for the immunochemical localization of ovalbumin in paintings: an advanced mapping detection approach
The Analyst, 2013
In the field of analytical chemistry, many scientific efforts have been devoted to develop experi... more In the field of analytical chemistry, many scientific efforts have been devoted to develop experimental procedures for the characterization of organic substances present in heterogeneous artwork samples, due to their challenging identification. In particular, performances of immunochemical techniques have been recently investigated, optimizing ad hoc systems for the identification of proteins. Among all the different immunochemical approaches, the use of metal nanoparticles - for surface enhanced Raman scattering (SERS) detection - remains one of the most powerful methods that has still not been explored enough for the analysis of artistic artefacts. For this reason, the present research work was aimed at proposing a new optimized and highly efficient indirect immunoassay for the detection of ovalbumin. In particular, the study proposed a new SERRS probe composed of gold nanoparticles (AuNPs) functionalised with Nile Blue A and produced with an excellent green and cheap alternative approach to the traditional chemical nanoparticles synthesis: the laser ablation synthesis in solution (LASiS). This procedure allows us to obtain stable nanoparticles which can be easily functionalized without any ligand exchange reaction or extensive purification procedures. Moreover, the present research work also focused on the development of a comprehensive analytical approach, based on the combination of potentialities of immunochemical methods and Raman analysis, for the simultaneous identification of the target protein and the different organic and inorganic substances present in the paint matrix. An advanced mapping detection system was proposed to achieve the exact spatial location of all the components through the creation of false colour chemical maps.
The stratigraphical characterization of polychrome samples may be considerably limited by sample ... more The stratigraphical characterization of polychrome samples may be considerably limited by sample preparation procedure both in terms of embedding material and surface polishing. Indeed, the use of synthetic embedding media may contaminate the sample, while the surface morphology obtained after polishing may affect the performances of different analytical techniques such as FTIR microscopy both in attenuated total reflection (ATR) and in total reflection mode. In particular, in ATR an optimal contact between the crystal and the sample is necessary, while in total reflection sample roughness affects the shape and the intensities of the spectra. Recently, different sample preparations were studied and compared taking into account the performance of FTIR microscopy in ATR mode but, as this approach presents some disadvantages, such as the risk of damaging the sample due to the pressure of the crystal, the present research work has been focused on total reflection, which works in non-contact mode. Two sample preparation methods based on the use of cyclododecane and KBr, recently proposed for their capability to reduce contamination effects, were selected to evaluate the performances of FTIR microscopy in total reflection mode on samples characterized by a different surface morphology. In particular the sample prepared with epoxy resin and CDD has been subjected to a simple cut, producing an inhomogeneous surface, with a high roughness, while the sample embedded with KBr has been prepared with a fine polishing procedure, obtaining an optically flat surface. Both of the preparation procedures were applied to obtain two paint cross-sections from fragments collected in the same area from a mural temple (15th century) located in Thubeken Lhakhang, Nepal. The cross sections were analysed with FTIR microscopy in total reflection mode, in order to compare the effect of the preparation methods on the spectral response. Line-scan imaging measurements were carried out on both of the samples and the resulting chemical images were reconstructed by a chemometric approach based on principal component analysis.
Few research studies from the early seventies reported the use of far infrared (FIR) spectroscopy... more Few research studies from the early seventies reported the use of far infrared (FIR) spectroscopy and its analytical potential. Especially in the field of cultural heritage, particular attention has not been given to this technique because of its destructive character; however, this can be overcome by employing Raman microscopy. Provided that enough quantity of the sample is available, FIR spectroscopy may represent a useful analytical method in the case of inorganic compounds that are not active in the mid infrared region and, because of the fluorescent effect produced by the organic media, not detectable even by Raman spectroscopy. In this article, the application of FIR spectroscopy has been applied for the characterisation of several inorganic pigments. A preparation method based on the use of polyethylene has been developed that allows analyses with moderate quantity of sample (0.5-1.5 mg). The data obtained have been compared with Raman results with the aim to build a common database. Some applications on real case studies are presented and discussed.
Metallographic features of ancient bronze artefacts often hide peculiar micro-chemical processes ... more Metallographic features of ancient bronze artefacts often hide peculiar micro-chemical processes and corrosion behaviours, which are worth to be studied as they can provide conservators and archaeologists with valuable tools and information. It is widely documented that Chinese bronzes were cast and the way to adjust their properties was to change the alloy composition. In particular, addition of lead, which is insoluble in the bronze matrix, results in the formation of inclusions or globules, which undergo oxidation processes leading to their conversion into corrosion products. The mechanisms through which this occurs were still poorly investigated. The present work was conducted to further study the corrosion behaviour of high-leaded bronze, especially focusing on the behaviour of lead globules. To this aim, a collection of Chinese archaeological bronzes, showing intermediate steps of degradation, were selected and investigated. The use of combined microscopy-based, molecular and elemental, analytical techniques allowed the characterization as well as the precise location of corrosion products, thus enabling us to propose a degradation pathway basing on thermodynamic data provided by Pourbaix diagram. The achieved results will be useful for researchers involved in these kinds of studies to better interpret data obtained.
The ability to analyse layers within a paint sample is important both for historical studies as w... more The ability to analyse layers within a paint sample is important both for historical studies as well as determining the most suitable method for restoration. The difficulty in physically separating these very thin layers makes detailed analysis difficult, and a combination of destructive and non-destructive techniques are needed. Laser pyrolysis/gas chromatography-mass spectrometry (LaPy/GC-MS) is a technique that has proved successful in the analysis of geological samples which pose the same difficulties for analysis, but it has not yet been tried on paint cross sections. This study presents preliminary results of applying LaPy/GC-MS on standard mock-ups for identification of organic compounds used as varnishes, binders and colourants. The technique was shown to be particularly effective for the identification and localisation of natural resins and synthetic colourants. Moreover, the integration between this technique and other stratigraphical analyses may allow the complete characterisation of the composition of organic substances in paint cross-sections.
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