10.6092/issn.1973-9494/9231
L’uso della termografia ha permesso di studiare un’antica chiesa vista da una prospettiva storica, per saperne di più sulle sue caratteristiche costruttive. Questa tecnica diagnostica non distruttiva ha permesso di condurre un’indagine stratigra­fica delle strutture in elevazione, ottenendo l’acquisizione di nuove informazi­oni e confermando la sua validità in questo complesso campo di applicazione. Questa fase iniziale dell’acquisizione delle conoscenze ha offerto l’opportunità di proporre una linea di studio da condurre attraverso l’applicazione di vari strumenti e tecniche, a partire dalla termografia, secondo un ordine razionale. I risultati strumentali delle indagini man mano che vengono eseguiti possono suggerire l’ubicazione dei punti in cui continuare le successive indagini, definendo allo stesso tempo linee guida appropriate per la valutazione dei risultati.
application/pdf
1973-9494
9231
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Francesco Miraglia
Conservation Science in Cultural Heritage
restoration
Use and Efficacy of Thermography for Stratigraphic Analysis of Historical Buildings
Text.Serial.Journal
https://conservation-science.unibo.it/
18
Articles
2018-12-31
2019-03-18
2018-12-31
2019-11-05
135-146
CSCH
Francesco Miraglia
2018/12/31
10.6092/issn.1973-9494/9231
135
Università della Campania "Luigi Vanvitelli", Naples
1973-9494
restoration
en
146
Use and Efficacy of Thermography for Stratigraphic Analysis of Historical Buildings
https://conservation-science.unibo.it/article/download/9231/9066
18
U     SE AND EFFICACY OF THERMOGRAPHY FOR STRATI-
      GRAPHIC ANALYSIS OF HISTORICAL BUILDINGS

    Cesare Crova*74
    Istituto Superiore per la Conservazione ed il Restauro,
    Ministero per i Beni e le Attività Culturali
    Rome, Italy

    Francesco Miraglia
    Dipartimento di Architettura, Università della Campania “Luigi Vanvitelli”
    Naples, Italy


    Keywords: thermography, historical buildings, stratigraphic analysis, restoration


    1. Introduction

   Non-destructive investigation techniques based on thermography in the infrared
spectrum are well known in the scientific literature, which provides a lengthy list of
publications. Most of these deal with its use in the field of civil and industrial main-
tenance; checking heating systems; predictive maintenance and safety; checking of
components for electricity generation installations; and for checking energy contain-
ment [1] [3] [6] [8-9].
   On the same wavelength are the UNI NorMal Recommendations: recommendation
n. 10824:2009 specifies the method for identifying defects of adhesion to the substrate




                                                                                                   CONSERVATION SCIENCE IN CULTURAL HERITAGE
of thin coverings (on the order of microns and of millimetres), applied to industrial
products and system components. The regulation applies to all industrial components
with a geometry that is such as to permit direct examination using a thermographic
system. Recommendation n. 18434:2011 provides a guide to the use of infrared ther-
mography (IRT) as part of a status monitoring programme and for the diagnostics of
the machines. Recommendation n. 16714-1:2016 describes the general principles for
applying thermography in non-destructive tests, to detect and locate discontinuities
(for example, hairline cracks, cracks, detachments and inclusions) in different materi-
als (composites, metals, and coverings).
   In construction, this technique verifies the presence of anomalies due to flawed
insulation, humidity, air infiltration, and the presence of pathologies, such as masonry
discontinuities. In the field of cultural heritage diagnostics, in-depth studies have been
performed at the environmental Physics and Control laboratory of the Istituto Superi-
ore per la Conservazione ed il Restauro since the early 1980s, yielding many articles
on the use of this technique for studying the causes and mechanisms of decay [11],
and initiating a series of more in-depth analyses on the issue of diagnostics aimed at
conserving the cultural heritage [5] [6] [8] [10].
   Non-destructive diagnostics is now frequently used by cultural heritage operators,
thanks to the spread – due to the contained costs and ease of use – of qualitative

*   Corresponding author: cesare.crova@beniculturali.it

                                                                                             135
                                                                                                               and quantitative tools to analyze historical construction. Its development is fostered
                                                                                                               by operating needs that characterize conservation of materials, especially with regard
                                                                                                               to investigating pathologies of decay and structural stability [5] [10]. Moreover, the
                                                                                                               availability of non-invasive diagnostic techniques like thermography has led to its use
                                                                                                               on a large scale, enabling the collection of data for more in-depth research or, alterna-
                                                                                                               tively, creating a knowledge base for restoration interventions. Among the diagnostic
                                                                                                               techniques used in the field of restoration, thermography is also preferred over slightly
C. Crova, F. Miraglia - Use and efficacy of thermography for stratigraphic analysis of historical buildings




                                                                                                               invasive ones, like endoscopy, and over-invasive, mechanical-type ones, such as flat
                                                                                                               jacks (in masonry), or pull-outs (in plaster structures) [1] [3].
                                                                                                                   The assay focuses on the use of this investigation technique in the non-invasive
                                                                                                               analysis of architectural surfaces, not only as work site preparation activities but aimed
                                                                                                               at the critical knowledge of the structure, of the elevation’s stratigraphy, and of its state
                                                                                                               of conservation. This technique was applied to examine the building fabric of the old
                                                                                                               centre of Sessa Aurunca, in the province of Caserta (Italy). The centre presents a
                                                                                                               palimpsest of Medieval construction techniques, in which successive layers of plaster,
                                                                                                               laid onsite over the course of centuries, have obliterated the information useful for
                                                                                                               documenting the growth of the inhabited area, still largely to be investigated.
                                                                                                                   The inspiration for the research project was provided by the removal of a portion of
                                                                                                               plaster from the Church of San Giovanni in Piazza (Figures 1-3), which cast light on a
                                                                                                               construction technique where recovered stone blocks were used as well as on the use
                                                                                                               of a corner column.
                                                                                                                   These particulars recall a manner of construction characteristic of the territory of
                                                                                                               Campania and Lazio (Benevento, Capua, Salerno, Sessa Aurunca, Fondi, Gaeta) [7].
                                                                                                               This made it possible to move the construction of the religious complex from the four-
                                                                                                               teenth back to the twelfth century. This then led to the decision to investigate the archi-
                                                                                                               tecture with the aid of thermography, used as an instrument for reading the elevation’s
                                                                                                               stratigraphy [6].
                                                                                                                   It emerged that the use of thermography is a knowledge process to be directed not
                                                                                                               only towards understanding the conditions of conservation, stability, deformations in
                                                                                                               progress, and a building’s alteration processes, but also towards investigating con-
                                                                                                               struction techniques. This is due to the fact that removal of the plaster is no longer
                                                                                                               required, as the work of studying the surfaces of the architecture can be done in an
                                                                                                               exclusively non-invasive manner. This results in the possibility of planning projects
                                                                                                               aimed at restoration, as well as historical investigation, thereby enabling an inspection
                                                                                                               of those previously inaccessible places, and providing information which would other-
                                                                                                               wise be unavailable or, in general, very limited in archival documents C.C.).


                                                                                                                  2. Objective and study methodology

                                                                                                                  Thermography makes it possible to acquire images in the infrared field (Figure 6),
                                                                                                               invisible to the human eye, without creating contacts between the diagnostic instru-
                                                                                                               ment and the analyzed object. In thermographic investigation, different materials are
                                                                                                               thermally excited, delivering different infrared radiations. The thermographic camera
                                                                                                               analyzes the heat an object emits in the infrared band, in order to build a radiometric-
                                                                                                               digital image in which surface temperatures can be displayed. The afore-mentioned
                                                                                                               temperatures are depicted in false colours that can consequently be distinguished by



                                                                                                         136
the human eye: the “cold” colours correspond to low temperatures and the “warmer”
colours to higher temperatures.
    In general, the temperatures are “described” with a palette of colours, widely used
in the construction field. In other cases, in consideration of the operator’s needs, one
may opt for a depiction in shades of grey or other colour combinations. The current
devices – usually provided with an uncooled microbolometer detector like the one used
in this investigation – are portable (of contained size and weight), precise (they can
assess temperature differences in the order of hundredths of a degree) and affordable.
They also make it possible to record digital videos and photos, which can be optimized
using dedicated software.
    For a good thermographic investigation, the item – free of reflecting or insulating
materials – must be thermally excited: an appropriate thermal gradient between its
surface and the surrounding environment must be allowed [1] [3]. When it is conducted
in the open, the investigation may be altered or compromised by wind, rain, direct sun-
light, or proximity of extraneous, high-temperature objects.
    For this reason, the choice of the time for conducting the thermographic survey is
also important and should be scheduled during afternoon hours, when the materials
begin to release the absorbed heat. If this is not possible, then the support should be
heated artificially to create conditions useful for the analysis.




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Figure 1. Sessa Aurunca (Caserta), orthophoto extract (from Google Earth). The highlighted area
shows the location of the church of San Giovanni in Piazza, between Corso Lucilio and Via Delio,
on the north-south axis that characterizes the articulation of the historic city.



    Not only does thermography make it possible to learn about the condition of a
structure as regards its conservation and stability, the deformations and the alteration
processes, such as humidity fronts and gaps in the plaster [9], it also allows the stra-
tigraphy of its elevations to be investigated. It therefore takes on an important role in



                                                                                                   137
                                                                                                               the science of restoring and conserving cultural heritage, representing an initial aid for
                                                                                                               acquiring information on a structure’s material characterization.
                                                                                                                  The investigation presented here, carried out by means of remote sensing thermog-
                                                                                                               raphy, employed mainly in construction, regards a religious building located in the old
                                                                                                               province of Terra di Lavoro (in northern Campania), a territory now belonging to the
                                                                                                               province of Caserta: the Church of San Giovanni in Piazza in Sessa Aurunca (F.M.).
C. Crova, F. Miraglia - Use and efficacy of thermography for stratigraphic analysis of historical buildings




                                                                                                               Figure 2. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. View of the façade on
                                                                                                               Corso Lucilio, highlighting the mediocre state of conservation of the finishings (photo: Francesco
                                                                                                               Miraglia).



                                                                                                                  3. Context and applications

                                                                                                                  Sessa Aurunca rises on a tuff plain over a very large territory, representing, from
                                                                                                               the western side, the outer boundaries of Campania towards lower Lazio. A colonia
                                                                                                               under Latin law, it became a municipium in 90 A.D. With the fall of the Roman Em-
                                                                                                               pire, it underwent a slow decline. It was one of the first Christian dioceses in northern
                                                                                                               Campania and in the late ninth century became a Lombard gastaldato. With Norman/
                                                                                                               Swabian domination, Sessa Aurunca began again to grow in importance, thanks to a
                                                                                                               vast programme of urban development.
                                                                                                                  The Angevin presence, on the other hand, was characterized by increased popula-


                                                                                                         138
tion in the northern quadrant of the settlement and fostered the development of new
religious buildings. The city took on a role of major importance during the fourteenth
century, with the rise of the Marzanos, the powerful family in the Kingdom of Naples
who made it the capital of their feudal holdings.
    Then, during the Aragonese domination, the Marzanos themselves made an impor-
tant and thoroughgoing transformation and strengthening of the masonry wall. When
Aragonese rule ended, Sessa was governed, starting in 1507, by Consalvo Ferrando
de Cordoba, the first Viceroy of Naples. In the early nineteenth century, the city saw
a phase of slow decline, without the influential families and the many religious orders
that for centuries had characterized its sociocultural arrangement [4].




                                                                                                              CONSERVATION SCIENCE IN CULTURAL HERITAGE
Figure 3. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. The base object of the
thermographic investigation. The portion on the left is substantially intact, although marked by
evident decay of the material; the portion on the right highlights a large gap in the plaster (photo:
Francesco Miraglia).



    The small sacred building is situated in the city’s ancient square from which it takes
its name (the Church was once known by the name “de platea”) and has already been
the object of an initial analysis by the authors [14]. It is dated to the fourteenth century,
with reports of additional interventions dating to the eighteenth century. Despite this, it
reveals complex stratigraphic traits. In fact, thermographic investigation has allowed it
to be dated to at least two centuries earlier.
    At about five metres above the road level, the second phase in the construction of
the Church (Figures 4-5) was visible, as ashlars of local grey tuff were used which, also
in this case, can be observed in a gap in the plaster of the upper portion of the façade,
revealing the masonry above (C.C.).




                                                                                                        139
C. Crova, F. Miraglia - Use and efficacy of thermography for stratigraphic analysis of historical buildings




                                                                                                               Figure 4. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. The portion of façade (right
                                                                                                               side) is useful for understanding the revealed masonry composed of blocks of reused limestone
                                                                                                               with a corner column and superimposed rows of ashlars making use of grey Campanian tuff
                                                                                                               (photo: Cesare Crova).




                                                                                                               Figure 5. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. The portion of façade (left
                                                                                                               side), does not show any useful elements for understanding the characterization of the masonry
                                                                                                               (photo: Cesare Crova).




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Figure 6. Representation of the electromagnetic spectrum indicating the thermal infrared field
[12].




                                                                                                       CONSERVATION SCIENCE IN CULTURAL HERITAGE




Figure 7. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. Thermogram of a portion
of the façade (right side) with seven surveys performed in the 15.6-24.6°C range, for a total
variation of 3.1°C (photo: Francesco Miraglia).




                                                                                                 141
                                                                                                                  4. Discussion

                                                                                                                  The validity of the results obtained from the thermographic investigations are also
                                                                                                               enhanced through a necessary phase of interpretation of the thermograms, performed
                                                                                                               using IT applications available in various proprietary or open source formats. In es-
                                                                                                               sence, a thermogram restores, for each individual pixel – with a range that imposes
                                                                                                               the minimum and maximum temperatures within which to operate – the thermal char-
C. Crova, F. Miraglia - Use and efficacy of thermography for stratigraphic analysis of historical buildings




                                                                                                               acteristics of the examined objects, thereby permitting, in the post-processing phase,
                                                                                                               an overview of the individual responses of these objects to infrared.
                                                                                                                  The thermographic investigation was programmed on the basis of the data provided
                                                                                                               by the theoretical model, in the choice both of the timing and modes of operation, in
                                                                                                               order to avoid the drawbacks that a survey conducted outdoors and in broad daylight
                                                                                                               might entail in recording surface thermal distribution [2].
                                                                                                                  The thermograms obtained with this research, done on 04 April 2018 from 2:30 to
                                                                                                               3:30 PM, delivered the following data. Emissivity: 0.80; reflected temperature: 22.0°C;
                                                                                                               distance: 3.0 m; relative humidity: 50%; atmospheric temperature: 20.0°C; transmis-
                                                                                                               sion: 0,0; IR window temperature: 25.0°C; IR window transmission IR: 1.00 (Figures
                                                                                                               7-9).




                                                                                                               Figure 8. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. Thermogram of a portion
                                                                                                               of the façade (left side). Two surveys are highlighted with an almost imperceptible relative
                                                                                                               variation (photo: Cesare Crova).

                                                                                                                  With a resolution of 640x480 pixels (considered high definition from a thermograph-
                                                                                                               ic standpoint), the thermograms were obtained with a Flirtm thermographic camera
                                                                                                               using MSX (Multi Spectral Dynamic Imaging) technology (Figure 10). Its integrated


                                                                                                         142
processor allows it to produce detailed images. With this technology, the details of
the digital photo are superimposed onto the thermal one, offering a sharper analysis
spectrum than that rendered by other devices. This technology makes it possible to
take advantage of the considerable amount of graphic information only found in digital
photographs (for example: overhanging elements, wall texture, etc.) (F.M.).


   5. Conclusions

   The experimentation presented here, originating from the loss of plaster on the right
side of the Church of San Giovanni in Piazza, shows that, with the use of thermog-
raphy, details of a structure different from those for which this type of investigation is
preferred by technical operators, may be easily analyzed.
   The initial knowledge phase which, with thermography, provides qualitative and “sur-
face” type values, must often be supplemented by additional diagnostic techniques, in
order to create a synergy among various methods. This achieves a broader path of
knowledge useful above all in the field of restoration, in which the interdisciplinary ap-
proach helps to discern complex problems and to define appropriate guidelines after
evaluating the results [8] [13].




                                                                                                         CONSERVATION SCIENCE IN CULTURAL HERITAGE




Figure 9. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. Thermogram of the
lower portion of the façade, obtained by comparing the temperatures of the analyzed points.
Two readings are highlighted, included in the 14.7-19.2°C range. Of note is the substantial
correspondence of emissivity (0.2°C), which demonstrates its thermal homogeneity. The dotted
line marks the coplanarity of the two readings: pointer 1, the horizontal break highlighted in
infrared on the left portion; pointer 2, the change in pitch in the masonry on the right (photo:
Francesco Miraglia).

   In conclusion, it is important to point out, however, that the use of non-invasive, non-
manipulative and non-destructive analytical technologies, including thermography, is
of great value for diagnostic-analyses and enables significant results to be obtained,
even though of a qualitative order, relating to the object being investigated. It is also
true that, considering the appropriate methodology used, it is also useful to use suit-


                                                                                                   143
                                                                                                               able invasive technologies, thus correctly and comprehensively providing a quantita-
                                                                                                               tive analytical framework.
C. Crova, F. Miraglia - Use and efficacy of thermography for stratigraphic analysis of historical buildings




                                                                                                               Figure 10. Sessa Aurunca (Caserta), Church of San Giovanni in Piazza. Thermogram of lower
                                                                                                               portion of the façade, performed to the right of the entrance portal. The application of MSX
                                                                                                               technology emphasizes a large number of details that would otherwise be impossible to highlight
                                                                                                               in a thermographic investigation, such as the texture of the various materials that have been
                                                                                                               examined (photo: Cesare Crova).



                                                                                                                     References

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                                                                                                                       edilizio. Milano: Franco Angeli.
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                                                                                                                       behaviour obtained through thermographic survey. In: Baer N.S., Sabbioni C.,
                                                                                                                       Sors A.L. (eds.), Science, Technology and European cultural heritage: proceed-
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                                                                                                                       co. Marina di Minturno: Caramanica Editore.

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        strumentali al convento dei Padri Serviti: approccio attivo consolidato ed innova-
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      Biographical notes

   Cesare Crova graduated in Architecture; he is a specialist in Restoration of monu-
ments and has a Ph.D. in Conservation of architectural heritage; he is a professor in
Architecture Pathology at ISCR SAF. He has carried out teaching and research at
IUAV, the “Sapienza” University of Rome, the University of Molise and the Cultural
Heritage Department at the University of Padua. He works in the field of cultural heri-
tage conservation, where he is part of several working groups at MiBACT, in addition to


                                                                                                    145
                                                                                                               planning and directing restoration work. He is the National Vice President of Italia Nos-
                                                                                                               tra and a member of the CDA of the Circeo National Park; he is a committee member of
                                                                                                               the UNI Technical Corps at UNI / CT 033 / SC 01 / GL 01 “Guidelines and terminology”
                                                                                                               and a member of MiBACT Unite 4 Heritage (MiBACT H4U), “Blue Culture Helmets “;
                                                                                                               he is an ordinary member of the “Centro di Studi per la Storia dell’Architettura” (Rome).

                                                                                                                  Francesco Miraglia graduated in Architecture; he has a Ph.D. in Conservation
C. Crova, F. Miraglia - Use and efficacy of thermography for stratigraphic analysis of historical buildings




                                                                                                               of architectural heritage; he is an architect, Honorary officer for the protection and
                                                                                                               supervision of the architectural heritage in the provinces of Caserta and Benevento
                                                                                                               (MiBAC), former Adjunct Professor of “Caratteri costruttivi dell’edilizia storica” (Uni-
                                                                                                               versità della Campania). He is the author of many studies on the protection of cultural
                                                                                                               heritage; he has been a member of local commissions for the landscape protection of
                                                                                                               several Italian municipalities. He is the coordinator of the scientific committee of “Terra
                                                                                                               Laboris. Itinerari di ricerca” (Caramanica Editore). Since 2006 he has been a member
                                                                                                               of “Società Napoletana di Storia Patria” (Naples). Since 2017 he has been an ordinary
                                                                                                               member of “Centro di Studi per la Storia dell’Architettura” (Rome). His professional
                                                                                                               activity is focused on the restoration and conservation of cultural heritage.

                                                                                                                   Summary
                                                                                                                   The use of thermography made it possible to investigate an ancient church viewed
                                                                                                               from a historical perspective, in order to learn more about its construction characteris-
                                                                                                               tics. This non-destructive diagnostic technique enabled a stratigraphic investigation of
                                                                                                               the structures in elevation to be conducted, resulting in the acquisition of new informa-
                                                                                                               tion and confirming the validity of its use in this complex field of application.
                                                                                                                   This initial phase of knowledge acquisition provided an opportunity to propose a
                                                                                                               line of study to be conducted through the application of various instruments and tech-
                                                                                                               niques, starting with thermography, in accordance with a rational order. Instrumental
                                                                                                               results of the investigations as they are carried out, might suggest the location of points
                                                                                                               in which to continue with subsequent investigations, while at the same time defining
                                                                                                               appropriate guidelines in assessing the results.

                                                                                                                  Riassunto
                                                                                                                  L’uso della termografia ha permesso di studiare un’antica chiesa vista da una
                                                                                                               prospettiva storica, per saperne di più sulle sue caratteristiche costruttive. Questa
                                                                                                               tecnica diagnostica non distruttiva ha permesso di condurre un’indagine stratigra-
                                                                                                               fica delle strutture in elevazione, ottenendo l’acquisizione di nuove informazi-
                                                                                                               oni e confermando la sua validità in questo complesso campo di applicazione.
                                                                                                               Questa fase iniziale dell’acquisizione delle conoscenze ha offerto l’opportunità di
                                                                                                               proporre una linea di studio da condurre attraverso l’applicazione di vari strumenti e
                                                                                                               tecniche, a partire dalla termografia, secondo un ordine razionale. I risultati strumentali
                                                                                                               delle indagini man mano che vengono eseguiti possono suggerire l’ubicazione dei
                                                                                                               punti in cui continuare le successive indagini, definendo allo stesso tempo linee guida
                                                                                                               appropriate per la valutazione dei risultati.




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