Indagini di imaging multispettrale e analisi di microFTIR per la caratterizzazione dei materiali originali e di restauro del globo celeste

Il contributo riporta i risultati analitici ottenuti sul globo di Vincenzo Coronelli finalizzati alla caratterizzione dei materiali originali utilizzati, nonchè quelli riscontarti come vecchi interventi di restauro. Le indagini sono state svolte con sistemi analitici non invasivi quali lo scanner multispettrale d'immagini nei range di lunghezza d'onda che vanno dal visibile, UV ed Infrarosso e micro nvasivi quali la microscopia ottica ed FTIR effettuata sia su sezioni stratigrafiche della superficie dipinta in modalità riflessione totale attenuata (ATR), che su micro particelle di campione analizzate con il sistema della micro cella di diamante in modalità trasmissione

FOURIER TRANSFORM INFRARED SPECTROSCOPY (FTIR)

The chapter deals with the application of FTIR and micro-FTIR spectroscopy to the scientific examination of paint cross sections. The kind of analyses, the basic principle as well as limits and advantages of the technique are highlighted

Innovative Treatments for the Protection of Outdoor Bronze Monuments

We present here the results so far achieved in the framework of the EUARTECH project, concerning the evaluation of innovative treatments used to preserve outdoor bronze. Traditional coatings, such as Incralac and/or synthetic waxes (R21, TeCe Wachs 3534F), were compared with different organo-silanes materials. In order to evaluate their effectiveness, applications were made on urban natural aged copper plates and also on parts of a work of art: the sceptre of the equestrian bronze statue of Bartolomeo Colleoni, in Venice. Electron impedance spectroscopy (EIS), ATR mapping FTIR microscopy and colorimetric measurements were performed after an 8-months exposure. The results clearly demonstrate how the corrosion resistance of some of the new tested treatments has the same order of magnitude of those commonly used at present, with the great advantage of having no modification in the colour appearance of the treated patina

ATR and transmission analysis of pigments by means of far Infrared Spectroscopy

In the field of FTIR spectroscopy, the far infrared (FIR) spectral region has been so far less investigated than the mid-infrared (MIR), even though it presents great advantages in the characterization of those inorganic compounds, which are inactive in the MIR, such as some art pigments, corrosion products, etc. Furthermore, FIR spectroscopy is complementary to Raman spectroscopy if the fluorescence effects caused by the latter analytical technique are considered. In this paper, ATR in the FIR region is proposed as an alternative method to transmission for the analyses of pigments. This methodology was selected in order to reduce the sample amount needed for analysis, which is a must when examining cultural heritage materials. A selection of pigments have been analyzed in both ATR and transmission mode, and the resulting spectra were compared with each other. To better perform this comparison, an evaluation of the possible effect induced by the thermal treatment needed for the preparation of the polyethylene pellets on the transmission spectra of the samples has been carried out. Therefore, pigments have been analyzed in ATR mode before and after heating them at the same temperature employed for the polyethylene pellet preparation. The results showed that while the heating treatment causes only small changes in the intensity of some bands, the ATR spectra were characterized by differences in both intensity and band shifts towards lower frequencies if compared with those recorded in transmission mode. All pigments' transmission and ATR spectra are presented and discussed, and the ATR method was validated on a real case study

Vaterite in the mortars of a mosaic in the Saint Peter Basilica, Vatican (Rome)

The vaults of the Saint Peter Basilica in Vatican (Rome) are decorated with wall mosaics whose realisation is dated to the end of the 16th century. The mortar layers beneath the mosaics are realised with the so-called \u201cRoman stucco\u201d, a kind of mastic specifically employed as a binder in the mosaic\u2019s backgrounds. Its empirical recipe was known and reported by 18th century authors, accounting for the use of lime, travertine powder added to a mixture of herbs and linseed oil. A recent restoration of the mosaics has allowed to characterise the mortars from a compositional point of view by individuating the inorganic mineralogical fraction and by chemically characterising the organic components. The study of stucco samples has been performed through polarising microscope observations, X-Ray Diffraction (XRD) analyses, Thermal Analyses (DTA and TGA), ATR-FTIR spectroscopy, Pyrolysis - gascromatography mass spectrometry (PY-GC). The analyses has allowed to distinguish between original stucco, produced and utilized at the same time of the realisation of the mosaics, and other mortars, presumably employed in later times during restoration interventions. The outcomes of the mineralogical and thermal analyses indicate the presence of four different types of stuccos, here considered as four characteristic groups. The mineralogical analyses indicate that all the samples are constituted of two main phases: calcite and vaterite and the thermal analyses, beyond the quantification of the calcium carbonate content, have shown the presence of organic components in the stucco. The organic fraction was characterised by Pyrolysis-gaschromatography \u2013 mass spectrometry, confirming the presence of the linseed oil cited in the ancient recipes. The very interesting outcome of this study is the occurrence of the rare calcium carbonate polymorph vaterite. The ATR-FTIR spectroscopy on the stucco gives further contribution to a better understanding of the FTIR spectrum of the rare mineral and an explanation of its formation is tentatively given

Scientific examination of the Mantegna's paintings in Sant'Andrea, Mantua: the families of Christ and St.John the Baptist and the baptism of Christ

The attribution of the paintings to Mantegna has been the subject of many controversial discussions among art historians, even though today it seems that, in spite of the fact that the paint surfaces were already badly cleaned and varnished since the beginning of the nineteen century, both paintings can be attributed to the last period of Mantegna’s painting activity. Therefore, with the purpose to complement the historical studies with the results of scientific examinations, the two paintings have been analysed in situ with the use of non-invasive portable analytical techniques, such as digital multi spectral scanner imaging system and X-Ray Fluorescence. It has been hence possible to evaluate the state of conservation, study applied artistic technique, distinguish and locate past restoration interventions and analyze colour and pigments. This has been particularly done by complementing the chemical information gathered through the use of XRF with the false-colour IR technique. The first analytical results seem to confirm that both canvas paintings have been prepared in the usual way with layers of gesso; the contemporary presence of elements such as Fe, Si, Mn and Al can be associated with the use of umber mixed with red ochre pigments. Mantegna was a supremely confident draughtsman and there is no evidence in his underdrawings of the use of any aids for the reproductions of cartoons or the enlargements of studies on paper. Instead, he seems to have drawn directly on the gesso making his first marks with a brush and very diluted carbon black ink, perhaps guided by a smaller scale sketch on paper. Once the placement of the main features was settled, Mantegna developed the underdrawing using a darker more pigmented liquid material still applied with a brush and contours were defined with broad, thick and fluent lines which have been also painted at sight. The modelling of forms has been achieved at the level of painted surfaces which seems to be a further indication of Mantegna’s late painting production. All these features seem to be present in both paintings. Particular attention was paid to the understanding of the material composition of the flesh paints. In fact, even though their composition resulted to be composed of lead white with different proportions of vermilion, they show different flesh tonalities such as the case of St Joseph and Zacharias and Christ and St John in The Families of Christ and St John the Baptist (under the name of Holy Family). To this regard the presence of possible pigment deterioration processes which may have taken place in the past are presented and discussed