O recozimento de azulejos à luz da abordagem teórica ao restauro

open2siUm trabalho exploratório realizado pelo LNEC em 2012 mostrou que o recozimento dos azulejos era tecnicamente viável como opção de restauro. O recozimento de azulejos de fachada enquanto alternativa à sua alienação não parece dever suscitar dúvidas de princípio. No entanto a simples perspectiva de se reabrir o processo tecnológico de fabricação em alto fogo conduz a argumentações metodológicas que não têm paralelo no caso dos restauros a frio. Esta comunicação aborda a questão do recozimento dos azulejos à luz da abordagem teórica ao restauro, mostrando que o processo não pode ser afastado com base em princípios sem se considerarem especificamente os casos em apreço e os ganhos expectáveis. Mas, apesar de não se terem identificado consequências danosas, a eventual aplicação do método a azulejos que não possam ser considerados um produto industrial carece ainda de estudos complementares quanto à perigosidade no longo prazo.openChaban, Antonina; Mimoso, João ManuelChaban, Antonina; Mimoso, João Manue

A combined non-invasive approach to the study of a mosaic model: First laboratory experimental results

This paper presents first laboratory results of a combined approach carried out by the use of three different portable non-invasive electromagnetic methods: Digital holographic speckle pattern interferometry (DHSPI), stimulated infrared thermography (SIRT) and holographic subsurface radar (HSR), proposed for the analysis of a custom-built wall mosaic model. The model reproduces a series of defects (e.g., cracks, voids, detachments), simulating common deteriorated, restored or reshuffled areas in wall mosaics. DHSPI and SIRT, already well known in the field of non-destructive (NDT) methods, are full-field contactless techniques, providing complementary information on the subsurface hidden discontinuities. The use of DHSPI, based on optical imaging and interferometry, provides remote control and visualization of surface micro-deformation after induced thermal stress, while the use of SIRT allows visualization of thermal energy diffusion in the surface upon the induced thermal stress. DHSPI and SIRT data are complemented by the use of HSR, a contact method that provides localized information about the distribution of contrasts in dielectric permittivity and related possible anomalies. The experimental results, made by the combined use of these methods to the identification of the known anomalies in the mosaic model, are presented and discussed here as a contribution in the development of an efficient non-invasive approach to the in-situ subsurface analysis of ancient wall mosaics

Wall Mosaics: A Review of On-Site Non-Invasive Methods, Application Challenges and New Frontiers for Their Study and Preservation

This review concerns the challenges and perspectives of on-site non-invasive measurements applied to wall mosaics. Wall mosaics, during the centuries, decorated numerous buildings, nowadays being part of world cultural heritage. The preservation and maintenance of these valuable decorations are undoubtedly directly dependent on identifying possible problems that could affect their hidden structure. On-site non-invasive methods, using different contact or no-contact technologies, can offer support in this specific field of application. The choice of the appropriate technique or combination of different techniques depends, in general, on the depth of investigation, the resolution, the possibility to have direct contact with the surfaces or, on the contrary, limited accessibility of the wall mosaics due to their location (e.g., vaults), as well as deterioration problems, (e.g., voids, detachments, or humidity effects). This review paper provides a brief overview of selected recent studies regarding non-invasive methods applied to the analysis of wall mosaics. This review, discussing the assessment of advantages and limitations for each method here considered, also considers possible future developments of imaging techniques in this specific context for cultural heritage applications

Non-invasive methods for the study of wall decorations in art history and archaelogy Metodi non invasivi per lo studio degli apparati decorativi di interesse archeologico e storico-artistico

Wall paintings and mosaics, especially those of archaeological and art historical interest, represent a complex object of study. They are characterized by the presence of a highly valuable decorated surface and several underlying preparation layers, acting as interface to the structural support. The presence of hidden defects within this structure can be related to the ageing and deterioration of materials, inhomogeneities can be the result of past restoration interventions on the ancient artwork. This thesis project introduces a combined in-situ non-invasive approach to characterize ancient wall decorations and their underlying support in art historical and archaeological field. For this purpose, experimental in-situ and laboratory tests are aimed to evaluate the applicability, potentialities and limitations of the combination of four portable electromagnetic methods: - Multispectral imaging (MI), using a modified camera with visible, infrared and ultraviolet filters (300-1000 nm), applied to analysis of the decoration layer; - Holographic subsurface radar (HSR), with 6.4-6.8 GHz antenna), applied to analysis of the shallow subsurface layers; - Infrared thermography (IRT), applied to analysis of the subsurface structure; - High resolution ground penetrating radar (GPR), with a full polar 2 GHz antenna for the investigation of the internal structure of the wall. Operating with different frequencies and related different penetration depth and resolution, these techniques can provide complementary information regarding the surface (i.e. materials, pigments, degradation phenomena, restorations etc.) and its underlying layers (i.e. structural integrity, differences in materials, presence of humidity, detachments, cracks etc.). The in-situ tests were performed on some representative case studies in Italy and Greece, which date to different periods and are characterized by different site conditions and conservation state of the analyzed decorations. The in-situ experimental approach, proposed in the thesis, was integrated by laboratory tests, using additional non-invasive methods: Digital Holographic Speckle Pattern Interferometry and Stimulated Infrared Thermography (DHSPI-SIRT). The experimental approach has shown that the applicability of in-situ methods is strongly conditioned by the intrinsic characteristics of decorated surfaces (high value, geometry, degradation state), to which the use of non-invasive contact methods (GPR and HSR) is limited. The in-situ results are strongly influenced by logistics and acquisition conditions. The key contribution of this thesis is evaluation of advantages and limitations of the tested in-situ non-invasive investigation approach for the diagnostics of ancient wall paintings and mosaics. This experimental research has shown that portability, remote access, immediate visualization and interpretation of data are crucial in the development of general guidelines (non-invasive investigation protocol) for the diagnostics of wall paintings and mosaics. These characteristics are essential for efficient interdisciplinary collaboration between scientists, art historians, archaeologists, conservators and curators, aimed at correct monitoring and conservation planning of wall paintings and mosaics.Pitture e mosaici parietali, soprattutto quelli di interesse storico-artistico e archeologico, rappresentano un oggetto di studio complesso. Oltre alla struttura fisica, generalmente costituita da una superficie esterna decorata e preziosa e dai diversi strati di preparazione che fungono da interfaccia con il supporto strutturale e che caratterizzano tutti i tipi di decorazioni parietali senza distinzione di tipologia e di epoca di realizzazione, si deve infatti tener conto anche della componente molto importante legata alla storia e alla vetustà  del manufatto. Questo comporta la possibilità  che ci siano presenti anomalie legate al degrado dei materiali e dei supporti e disomogeneità  legate ai restauri che possono aver interessato l'opera nel tempo. La possibilità di ottenere informazioni preliminari in modo non invasivo su tutti gli strati e sulle eventuali anomalie ivi presenti, costituisce pertanto un punto chiave nella diagnostica in-situ delle decorazioni parietali soprattutto per quelle di interesse storico-artistico o archeologico. Il presente progetto di ricerca, attraverso un approccio di tipo sperimentale, mira a testare le potenzialità e limiti di alcuni metodi elettromagnetici per indagini in situ di tipo non invasivo su pitture e mosaici parietali antichi. A tale scopo, sono stati presi in considerazione quattro diversi metodi di indagine: - l'Imaging Multispettrale (MI), utilizzando una macchina fotografica modificata e quattro differenti filtri (VIS-UV- e tre bande IR), per analisi, nel range 300-1000 nm, sulla superficie esterna decorata; - il Radar Olografico (HSR), utilizzando un'antenna con 5 frequenze comprese tra 6.4 GHz e 6.8 GHz, per l'analisi dei primi strati al di sotto della superficie esterna decorata; - la Termografia infrarossa (IRT), per l'analisi delle anomalie sub-superficiali; il georadar (GPR) ad altissima risoluzione, con un'antenna full polar da 2 GHz, per l'analisi della struttura interna dell'apparato murario al di sotto della superficie decorata. Operando con frequenze diverse, corrispondenti a profondità di indagine e risoluzioni differenti, queste tecniche possono in generale fornire informazioni preliminari sulla superficie (per esempio su materiali, pigmenti, stato di degrado, precedenti interventi ecc.) e sugli strati sottostanti (integrità strutturale, differenze nei materiali, presenza di umidità, distacchi, crepe, ecc.). Le misure in-situ sono state condotte su alcuni casi studio rappresentativi in Italia e in Grecia, relativamente a manufatti che risalgono a epoche diverse, in differenti contesti e differenti stati di conservazione. L'approccio sperimentale ha dimostrato che l'applicabilità dei metodi in situ è fortemente condizionata dalle caratteristiche intrinseche delle superfici di pregio (alto valore storico artistico, geometria, stato di degrado), che limitano l'uso dei metodi non invasivi a contatto (GPR e HSR) e che i dati sono inoltre fortemente dipendenti dalla logistica e dalle modalità di acquisizione. La sperimentazione in situ proposta nella tesi è stata integrata con test di laboratorio, utilizzando anche altri metodi non-invasivi, quali l'interferometria olografica e termografia infrarossa attiva (DHSPI-SIRT). Questo lavoro di ricerca ha evidenziato che portabilità, uso a distanza, immediata visualizzazione e interpretazione dei dati sono elementi cruciali nello sviluppo di un approccio non invasivo alla diagnostica di pitture murali e mosaici e risultano fondamentali per la caratterizzazione preliminare, per l'efficiente monitoraggio, la corretta diagnosi e l'adeguata pianificazione degli interventi sulle decorazioni parietali di interesse storico-artistico e archeologico nell'ottica di un'efficace collaborazione interdisciplinare tra componente scientifica e umanistica (storici dell'arte, archeologi) e con conservatori e curatori di questi preziosi beni

Wall Mosaics: A Review of On-Site Non-Invasive Methods, Application Challenges and New Frontiers for Their Study and Preservation

This review concerns the challenges and perspectives of on-site non-invasive measurements applied to wall mosaics. Wall mosaics, during the centuries, decorated numerous buildings, nowaday being part of world cultural heritage. The preservation and maintenance of these valuable decorations are undoubtedly directly dependent on identifying possible problems that could a\ufb00ect their hidden structure. On-site non-invasive methods, using di\ufb00erent contact or no-contact technologies, can o\ufb00er support in this speci\ufb01c \ufb01eld of application. The choice of the appropriate technique or combination of di\ufb00erent techniques depends, in general, on the depth of investigation, the resolution, the possibility to have direct contact with the surfaces or, on the contrary, limited accessibility of the wall mosaics due to their location (e.g., vaults), as well as deterioration problems, (e.g., voids, detachments, or humidity e\ufb00ects). This review paper provides a brief overview of selected recent studies regarding non-invasive methods applied to the analysis of wall mosaics. This review, discussing the assessment of advantages and limitations for each method here considered, also considers possible future developments of imaging techniques in this speci\ufb01c context for cultural heritage applications

Agar Gel as a Non-Invasive Coupling Medium for Reflectance Photoacoustic (PA) Imaging: Experimental Results on Wall-Painting Mock-Ups

The new reflectance set-up configuration extended the applicability of the photoacoustic (PA) imaging technique to art objects of any thickness and form. Until now, ultrasound gel or distilled water have been necessary as coupling mediums between the immersion-type transducer and the object’s surface. These media can compromise the integrity of real artwork; therefore, known applications of reflectance PA imaging have been limited to only experimental mock-ups. In this paper, we evaluate an alternative non-invasive PA coupling medium, agar gel, applied in two layers of different consistency: first, rigid—for the protection of the object’s surface, and second, fluid—for the transducer’s immersion and movement. Agar gel is widely used in various conservation treatments on cultural heritage objects, and it has been proven to be safely applicable on delicate surfaces. Here, we quantify and compare the contrast and signal-to-noise ratio (SNR) of PA images, obtained in water and in agar gel on the same areas, at equal experimental conditions. The results demonstrate that the technique’s performance in agar is comparable to that in water. The study uncovers the advanced potential of the PA approach for revealing hidden features, and is safely applicable for future real-case studies

Revealing Underdrawings in Wall Paintings of Complex Stratigraphy with a Novel Reflectance Photoacoustic Imaging Prototype

Revealing precious hidden features by a completely non-invasive approach is one of the crucial issues in the Heritage Science field. In this regard, concealed fresco paintings still represent an analytical challenge. This paper addresses the specific issue in wall painting diagnostics by the photoacoustic (PA) imaging technique, already proven to be efficient in revealing underdrawings and internal stratigraphy in movable paintings on paper and canvas. A newly set-up reflection PA prototype was applied here for the first time to probe the charcoal, graphite and sinopia hidden sketch drawings in concealed (gypsum, limewash, overpainted) wall paintings. The results presented here push forward the frontiers of the PA imaging technique and point to its potential effectiveness of revealing hidden underdrawings in historical wall paintings with complex stratigraphy

Revealing Hidden Features in Multilayered Artworks by Means of an Epi-Illumination Photoacoustic Imaging System

Photoacoustic imaging is a novel, rapidly expanding technique, which has recently found several applications in artwork diagnostics, including the uncovering of hidden layers in paintings and multilayered documents, as well as the thickness measurement of optically turbid paint layers with high accuracy. However, thus far, all the presented photoacoustic-based imaging technologies dedicated to such measurements have been strictly limited to thin objects due to the detection of signals in transmission geometry. Unavoidably, this issue restricts seriously the applicability of the imaging method, hindering investigations over a wide range of cultural heritage objects with diverse geometrical and structural features. Here, we present an epi-illumination photoacoustic apparatus for diagnosis in heritage science, which integrates laser excitation and respective signal detection on one side, aiming to provide universal information in objects of arbitrary thickness and shape. To evaluate the capabilities of the developed system, we imaged thickly painted mock-ups, in an attempt to reveal hidden graphite layers covered by various optically turbid paints, and compared the measurements with standard near-infrared (NIR) imaging. The obtained results prove that photoacoustic signals reveal underlying sketches with up to 8 times improved contrast, thus paving the way for more relevant applications in the field

Fluorescence Lifetime Phasor Analysis and Raman Spectroscopy of Pigmented Organic Binders and Coatings Used in Artworks

Fluorescence analysis of materials used as binders and coatings in artworks is often hampered by numerous factors, leading to uncertainties in data interpretation. Fluorescence lifetime (FL) measurements enable improvement of the specificity with respect to steady-state measurements by resolving the decay dynamics of the fluorophore emissions. In this work, layers of natural resin, oil, and wax—in pure form, pigmented, in mixtures, and spread on different substrates—were analyzed using a compact, portable, fiber-based FL instrument. FL data were processed via the phasor method and integrated with Raman spectroscopy to obtain complementary chemical information on the different substances. It was observed that the τ-phase of the mixtures is affected by both the pigments and the dispersing medium, and that the presence of the metal substrate contributes to changes in the FL of mixtures. The results obtained with our portable FL system combined with Raman spectroscopy pave the way for a systematic study of a larger number of materials for future in situ applications on works of art