diagnostics and protection of hagia sophia mosaics
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Journal of Cultural Heritage 14S (2013) e133–e139
Available online at
www.sciencedirect.com
iagnostics and protection of Hagia Sophia mosaics
ntonia Moropoulou ∗, Asterios Bakolas , Maria Karoglou , Ekaterini T. Delegou ,yriakos C. Labropoulos , Nikolaos S. Katsiotis
ational Technical University of Athens, School of Chemical Engineering, Section of Materials Science & Engineering, 9 Iroon Polytechniou Str., Zografou Campus, Athens, 15780,reece
a r t i c l e i n f o
rticle history:eceived 19 November 2012ccepted 16 January 2013vailable online 18 February 2013
eywords:
a b s t r a c t
Non-destructive techniques (ground penetrating radar, infra-red thermography, fibre-optics microscopy)were employed on south upper gallery mosaic areas of Hagia Sophia. The main aim of this on-site inves-tigation was to evaluate the preservation state of the mosaics and the previous interventions, as well asto detect mosaics in layers below the external plastered surfaces. Results indicated that is indeed pos-sible with the aid of NDT to locate the grid of rendered mosaics. Additionally the main environmentaldecay factors (moisture, salt, pollutants), areas where the mosaic materials (tesserae and bedding mor-
on-destructive testingibre optics microscopyround penetrating radar
nfrared thermographyagia Sophiaonument mosaics
tars) presented decay problems and sub-layers that pose risk of detachment or decay intensification,were identified. In this way, NDT can contribute to the development of a strategic planning for mosaicsconservation, protection and revealing. In addition, consolidation materials already used in conserva-tion interventions were assessed, with the aid of ageing tests and innovative restoration materials andtechniques are proposed for mosaics sustainable protection.
edding mortarsesserae
. Research aims
In this work, the main research aims concern the application ofon destructive techniques to:
detect rendered mosaics, and provide an indication of the mosaicgrid;assess the preservation state of mosaics, regarding the identifi-cation of defects (cracks, delaminations, voids, loss of adhesionwith the substrates, etc.) in rendered or uncovered mosaics, andthe determination of decay factors and products;assess of the performance of previous conservation interventions.
. Introduction
The church of Hagia Sophia in Constantinople is an importantonument of the international cultural heritage, on account of its
nrepeatable structural combinations and unique internal mosaicecoration. The church is decorated with mosaics dating back to
he fourth century; however, throughout its history the buildingas been damaged by earthquakes, vandalism, and has been theubject of various interventions. Regarding the mosaic decorations,∗ Corresponding author.E-mail addresses: [email protected], [email protected],
[email protected], [email protected], [email protected],[email protected] (A. Moropoulou).
296-2074/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved.ttp://dx.doi.org/10.1016/j.culher.2013.01.006
© 2013 Elsevier Masson SAS. All rights reserved.
a significant portion of the mosaic decoration that has survivedthrough centuries, has been covered during the conversion andsubsequent use of Hagia Sophia as a Mosque. Since 1935, whenHagia Sophia was converted into a museum, conservation of theremaining non-covered mosaics has begun, and also mosaics thathave been revealed from areas where the plaster was removed.
In the context of a bilateral Greek–Turkish cultural cooperationagreement [1] an array of non-destructive techniques has beenused in the past for the assessment of the preservation state ofthe structure of the church of Hagia Sophia [2,3] and its mosaicdecoration [4–10]. This past experience demonstrated the abilityof non-destructive techniques to reveal information necessary foreffective conservation interventions. A previous diagnostic studyusing Non Destructive Techniques (NDT) on the dome mosaics byNational Technical University of Athens (NTUA) research team hadbeen carried out in 2000 with the collaboration of UNESCO conser-vation team, under the permission of the former Director of HagiaSophia Museum S. Turkoglu.
A diagnostic study using NDT on the south upper gallery mosaicsby NTUA research team, took place in 2010 in the framework ofELAICH course (EUROMED Heritage IV Program), which was coor-dinated by the Bogazici University and Prof. M. Erdik (scientificresponsible), under the permission of A. H. Dursun, Presidentof Hagia Sophia Museum. In the south upper gallery area, plas-
tered surfaces, dating back to Fossati interventions (1847–1849)were partially uncovered and cleaned by the Byzantine Institutebetween 1931 and 1949 [11]. Recently, Istanbul Directorate ofSurveying and Monuments, Ministry of Culture and Tourism of
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urkish Republic, performed incisions on plastered areas revealingnderlying mosaics.
This NDT study aims to contribute to the development of atrategic planning for mosaics conservation, protection and revea-ing, by evaluating the preservation state of the mosaics, andssessing the performance of previous conservation/restorationnterventions, in order to plan and apply, on a pilot scale, compat-ble interventions for bedding mortars and tesserae consolidationnd protection.
. Experimental procedures and techniques
The surfaces under investigation were selected based on sev-ral criteria and approved by the Museum Technical Directorate.hree areas were investigated located at gallery level (Figs. 1 and 2).rea 1 of investigation is located at a perpendicular intersectionf two arches (a north east bracing arch) and it includes recentlyevealed ornamental mosaic areas, exposed brick structure andxposed stone structure. Area 2 is located between windows at theouth masonry of the south upper gallery. Part of the plastered areaas been removed revealing the underlying mosaic. The interest-
ng thing about this area, in comparison to Area 1, was the fact thathis is located on the interior of an external wall, thus is exposed tohe effect of exterior environmental factors. Both areas contained
osaics revealed by recent conservation/restoration interventions.owever, there were indications that mosaics were present in thedjacent areas, and thus the NDT were employed to verify thesessumptions and applied both on revealed mosaics, and plasteredurfaces. Area 3, corresponds to an already revealed figural mosaicf Constantine IX and Zoe by Byzantine Institute. In this case NDTas applied in order to diagnose the preservation state of mosaic.
his mosaic is also located on the interior of an east externalasonry, and a past cement intervention is present at its lower
art.In particular for the in situ investigation of gallery mosaics,
round penetrating radar (GPR), infrared thermography and fibreptics microscopy (FOM), were used:
Fig. 2. Surfaces of i
Fig. 1. Ground plan of Hagia Sophia at gallery level and above with areas underinvestigation [12].
• GPR: A ProEx system from MALÅ with 1.6 GHz and 2.3 GHz HighFrequency (HF) antennas and Groundvision 2 software was usedfor data acquisition, whereas data processing took place usingRadExplorer v.1.41;
• an infrared camera FLIR Therma Cam B200, having a detectorof focal plane array microbolometer in the spectral range of7.5–13 �m, with thermal sensitivity of 0.08 ◦C;
• fibre optics microscopy (FOM) i-scope – Moritex, was applied in
several magnifications (×30, ×50 and ×120).In addition the environmental parameters (Relative Humidity(%), Temperature (◦C) were recorded during the measurements).
nvestigation.
A. Moropoulou et al. / Journal of Cultural Heritage 14S (2013) e133–e139 e135
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Fig. 3. Thermograph
. Results and discussion
.1. First investigation surface at the South Gallery
The first mosaic area studied was located at the perpendicu-ar intersection of two arches and it includes recently revealed
osaic areas, exposed brick structure and exposed stone struc-ure (photograph 1 of Fig. 2). The remaining part, as most ofhe neighbouring areas is covered with plaster. The GPR scansocused on the revealed mosaic areas, where the exterior plas-er has been removed and aimed to assess the cohesion state ofhe mosaic with the underlying mortars and the masonry struc-
ure, as well to reveal any other imperfections. The cohesion ofhe tesserae with the base mortar at the preserved arch mosaicppears to be satisfactory with no apparent detachment of the glassig. 4. Images of Fibre optics microscopy: ornamental mosaic, north east bracing arch, Soud) red tessera, (×120); (e) dark green tesserae, (×50); (f) bedding mortar (×50); ornamessera, (×50); (i) black tessera, (×120).
aic-plaster interface.
tesserae layer, as indicated by the lack of targets corresponding tovoids.
In addition infrared thermography was applied. First scope ofthe investigation was to reveal any covered mosaics. Furthermore,infrared thermography was performed for the investigation of thefinishing layer (plaster), looking for delaminations, the evalua-tion of ageing and decay of materials due to porosity, cracking,water intrusion and the identification of possible level of mois-ture in the materials. Fig. 3 is a thermal image of the interfaceof plaster and revealed mosaic. The investigation showed a tem-perature difference between the plastered surface and the mosaicof a mean value of 1.1 ◦C (plastered surface presented higher
temperatures). This difference can be attributed to the differentemissivity of the two surfaces, as well to their different struc-ture and physicochemical characteristics. The plaster width madeth Gallery: (a) blue tessera, (×50); (b) gold tessera, (×120); (c) blue tessera, (×120);ental mosaic, south masonry, South Gallery: (g) black tessera, (×120); (h) black
e136 A. Moropoulou et al. / Journal of Cultural Heritage 14S (2013) e133–e139
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ig. 5. Top: Location of GPR scans A21-A25. Lower: GPR A21, A22 and GPR A23-Apaces below the plastered mosaic layer has been identified by GPR, are highlighted
t impossible to trace underneath existed mosaics with the use ofassive thermography. The temperatures at each different surfaceplaster-mosaic) did not presented high variations. In the mosaicurface bedding mortar presented higher temperatures than glassesserae.
In order to assess the preservation state of mosaic materialsbre optics microscope (FOM) was used. The major decay pat-erns presented on the glass tesserae (metallic and coloured) ofhe investigated mosaic surface, based on FOM results (Fig. 4), cane summarized as following: pitting, (Fig. 4a), dulling on the tophin transparent glass layer (cartellina) of the gold tessera, alongith extended fracturing of the gold leaves (Fig. 4b), lamination
nd iridescence, (Fig. 4e), salt efflorescence, (Fig. 4d), grey crustsnd fibrils of biogenic origin, (Fig. 4e), off-white coloured crusts,Fig. 4c) and micro-cracking and crizzling, (Fig. 4b). Water is the
rimary agent of the environment for causing glass deterioration13].Finally, the FOM examination of bedding mortar demonstratedhat straws were used for its construction, as well as that a projected
ults. The proposed areas around the revealed mosaic where the presence of void the patterned grey area.
part of straw is biodeteriorated (Fig. 4f). The use of straws in thebedding mortars of Hagia Sophia mosaics is also verified in a previ-ous work of our research team, when a fragment of a 10th centurydome mosaic was examined [6]. Additionally, straws were foundwithin a Fossati restoration plaster positioned between the inter-face of a joint area of 6th and 10th century mosaics on the dome[4].
4.2. Second investigation surface at the South Gallery
The second area studied was located between windows at thesouth masonry of the south upper gallery (Fig. 2a, b). Part of theplaster has been removed, revealing the underlying mosaic. Exter-nal damage to the plaster and the mosaic is observed at the lowerpart of the area due to moisture problems. Regarding the GPR mea-
surements, the aim was to assess the possibility of further presenceof mosaic below the plastered area and to evaluate the risk ofdetachment of the mosaics (revealed or plastered) (Fig. 5). Scanswere performed both horizontally and vertically. Two targets (void
A. Moropoulou et al. / Journal of Cultural Heritage 14S (2013) e133–e139 e137
Fig. 6. Images of Fibre optics microscopy; figural mosaic of Emperor Constantine IX Monomachos and Empress Zoe with Christ enthroned, east masonry, South Gallery: (a)s (d) d
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tone tesserae, (×30); (b) stone tesserae, (×30); (c) red coloured setting bed, (×30);
paces below the mosaic layer) were indicated in the scan withashed curves. The systematic scanning of area 2 revealed the pres-nce of an underlying mosaic layer, beyond the portion that haseen revealed by the removal of the plaster, but it also revealedoid spaces below this mosaic layer that need to be paid attentionf it is decided in the future to reveal a larger portion of the mosaic.fter correlation of the positions of these void spaces in the respec-
ive horizontal and vertical scans, a “map” of their position can beade.The infrared thermography results demonstrated, as in Area 1,
hat the plastered surface presented higher temperatures in com-arison to mosaic surface (about 0.6 ◦C), but the temperatures were
bit higher than area 1, which can be attributed to the fact thathis area was located at the internal surface of an external masonryFig. 1).
FOM examination of this mosaic area indicated that the blackesserae presented extended pitting, lamination and iridescenceFig. 4i). Salt efflorescence, (Fig. 4g) are observed, whereas off-whiteoloured crusts, (Fig. 4h), along with micro-cracking and crizzling,Fig. 4g, i) is clearly evident.
.3. Third investigation surface at the South Gallery
GPR scans showed the mosaic bedding mortar appears to haveood adhesion with the masonry structure and of good homogene-ty. Of interest are the different patterns observed at the locationsorresponding to the Empress Zoe’s face and hand. This can bettributed to the different materials and techniques used for theseosaics parts compared to the rest of the panel. This is verified
y bibliographic references. In particular, the three heads are laterestorations dating back to the end of 11th century [14]. The lower
art of the mosaic has been lost and a cement based mortar haseen applied. The main body of Empress Zoe has lost most of thelass tesserae and the mosaic setting bed is exposed. However, herpper portion is preserved. It is well known that flesh areas of Hagiaark coloured setting bed (×30).
Sophia figural mosaics were set by fine grained stone tesserae,whereas shadings were set by glass tesserae of various colours. Thetesserae used in the faces can be occasionally as small as 3 mm2
[15]. Whittemore notes that in the head of Zoe there is an incision of5 mm, forming a depression in the surface of the rest mosaic panel.Furthermore, Whittemore states that the tesserae of the Zoe headare “of another cutting than those of the hands in the earlier mosaic”[16].
The infrared thermography results displayed temperature vari-ations among the different building materials of the investigatedsurface. Cement based restoration plaster presented higher tem-peratures in comparison to mosaic surface (about 1 ◦C). Moreover,areas of possible defaults are rendered by higher temperatures andpointed out at the thermographic images.
Additionally, FOM examination of the stone tesserae of thefigural mosaic, presented: discoloration, black depositions, disinte-gration and superficial material loss (Fig. 6a, b), as well as biodecay,and salt efflorescence (Fig. 6b).
In parallel, the FOM investigation of the setting bed of themosaic, (which became observable due to tesserae detachmentat its lower part), demonstrated the presence of colouring pro-cess on the plaster, verifying corresponding historic data (Fig. 6c,d). Fresco technique was used for setting bed colouring, in orderfor the mosaicists to control the lay out of the tesserae [11]. Allthe investigated coloured setting bed areas presented black-greydepositions of biogenic origin, as well as superficial micro-crackswhich are developed due to bio-deterioration (Fig. 6c, d). Thepresence of water and, above all, accumulated moisture, is avery important factor initiating and sustaining forms of decayat mosaics’ construction materials, that is tesserae and bed-ding mortars [13]. Salt efflorescence and biodecay development,
demonstrated that moisture is accumulated on the investigatedmosaic. Therefore, moisture presence and salts crystallizationin bedding mortars result in tesserae detachment and biodecaydevelopment.
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Based on the results from all three investigated surfaces, it cane concluded that Non Destructive Techniques:
are effective in detecting rendered mosaics, and provide an indi-cation of the mosaic grid;can contribute to the assessment of the preservation state ofmosaics. In particular, defects (cracks, delaminations, voids, etc.)and decay factors and products can be determined. Therefore, it isconcluded that all the investigated mosaics presented extendeddecay due to moisture accumulation which resulted in the evi-dent decay factors of salt crystallization and biodecay, to thetesserae and bedding mortars examined;can assess the performance of previous conservation interven-tions (Fossati plastered surfaces). Regarding Fossati restorationplasters, the question if they are still accomplishing their restora-tion purposes, in the case of consolidation of the underlyingmosaics, can be posed. If the reason of the mosaics coating is toconsolidate them, consolidation treatments should be searchedout through the application of compatible bedding mortars andrevealing of mosaics, according to international deontology ofrevealing materials and art surfaces of high aesthetics. There-fore, innovative materials and techniques could be applied inorder to increase mosaics life-time for their sustainable protec-tion. Under this perspective the NTUA research team attempted toassess the performance of consolidation materials already usedin the dome mosaics by Central Laboratory for Restoration andConservation (Istanbul), together with international experts fromseveral countries and it was supported by UNESCO World CulturalHeritage Center. This project primary aim was to stabilize themosaics vulnerable areas and later painted surface decoration, inthe northeast and northwest quarter of the dome. Consolidation,grouting and mortar refills were applied where necessary. Par-aloid B72 (Ethyl methacrylate co-polymer in acetone dispersion),was used for consolidation treatments, according to the conser-vation team worked at the restoration works of dome mosaics.
In order to assess the compatibility and suitability of theforementioned consolidation material a new methodology waseveloped, which included various steps [17]:
construction of mosaic templates using the reverse engineeringmethodology;templates decay evaluation with ageing tests (Na2SO4 and freezethaw cycles);study and evaluation of consolidants (Paraloid B72 and PrimalA33 - Primal, is a consolidant widely used in conservation treat-ments, of the same category with Paraloid, and it was used inorder to have comparable results in the evaluation of both con-solidants’ performance);ageing tests on consolidated samples;assessment of the performance of the consolidated samples. Theageing tests of the consolidation materials that have alreadybeen used for the conservation of the dome mosaics indicatedunsatisfactory performance. New consolidation materials such asnano-lime, and particle modified consolidants are proposed beapplied and evaluated in both laboratory and monument scale.
. Conclusions
In situ application of NDT & Evaluation techniques like
round penetrating radar, infrared thermography and fibre opticsicroscopy, presented useful conclusions regarding the preser-ation state of the investigated mosaics materials, as well as theompatibility assessment on previous conservation interventions.
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Their application constitutes an integrated assessment methodol-ogy for the onsite diagnostic study of mosaics surfaces.
Moreover for the sustainable mosaic protection new consolida-tion materials should be tested, since the materials already usedlack of satisfactory lifetime performance.
Acknowledgements
Acknowledgements are attributed to all the people who havecontributed to the realization of this project. Special thanks aregiven to Sevinc Ozek Terzi, Director of Urban Projects, Istanbul2010, European Capital of Culture, Dr. Hasan Fırat Diker, Istan-bul Directorate of Surveying and Monuments, Ministry of Cultureand Tourism of Turkish Republic, Ahmet Haluk Dursun, Direct.Archaeological Museum of Istanbul, Prof. Mustafa Erdik, BogaziciUniversity.
Part of the study has been carried out under the sup-port of the research program: THALIS-NTUA-Sustainability andCompatibility of advanced materials and technologies for theprotection of cultural heritage monuments: Development of inves-tigation criteria and methodologies-COMASUCH. This researchhas been co-financed by the European Union (European SocialFund – ESF) and Greek national funds through the OperationalProgram “Education and Lifelong Learning” of the National Strate-gic Reference Framework (NSRF) – Research Funding Program:THALIS Investing in knowledge society through the EuropeanSocial Fund.
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