Diagnosing Hagia Sophia's Historic Mosaics

Educational Linkage Approach In Cultural Heritage

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Advanced Topic
Module 2 Knowing the built heritage
Topic 2.8 Diagnostic study of the Hagia Sophia mosaics

Prof. Antonia Moropoulou - NTUA – National Technical University of Athens


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Abstract The current presentation demonstrates the integrated diagnostic study performed on the
Hagia Sophia’s dome mosaics, aiming to evaluate their preservation state.

This evaluation is accomplished at two levels. The first, at the laboratory scale involves
characterization of materials with analytical techniques. The second, at the monument
scale, involves non-destructive techniques (NDT) for diagnosing the decay of the mosaics.
The laboratory characterization of materials is performed on samples of 6th and 10th
century mosaics, and their bedding mortars. Before in-situ diagnosis of decay is
performed, NDT validation at the laboratory is developed to ensure that the non-
destructive techniques reveal the true state of decay in-situ.



Content 
Table of contents of this presentation
A VERY short history of Hagia Sophia’s mosaics
 Hagia Sophia dome mosaics – review
 Evaluation of the preservation state
 Pilot panel with plastered mosaic for laboratory NDT investigation
 Diagnostic study (Lab) – 6th cent. glass tesserae
 Diagnostic study (Lab) – 10th cent. glass tesserae
 Diagnostic study (Lab) – Bedding mortars
 Diagnostic study (in-situ)
 Surface ET
 Surface PST
 Surface PSKT

iagnostic study (in-situ) - Conclusions

eferences



Diagnostic study
of the Hagia Sophia dome mosaics

Prof. A. Moropoulou
E. Aggelakopoulou, A. Aggelopoulos, N. Avdelidis, A. Bakolas, G. Charalampopoulos,
E. T. Delegou, M. Giannoulaki, M. Karoglou, K. Labropoulos, P. Karmis

NATIONAL TECHNICAL UNIVERSITY OF ATHENS
School of Chemical Engineering
Laboratory of Materials Science and Engineering

Prof. Antonia Moropoulou – Topic 2.6: Mosaics


A VERY short history of the Hagia Sophia’s Mosaics
The emperor Justinian I, inaugurated the new basilica of Constantinople, named “Ναός τῆς Ἁγίας τοῦ Θεοῦ Σοφίας”
(Church of the Holy Wisdom of God – Hagia Sophia) on 27 December 537. The mosaics inside the church were only
completed under the reign of Emperor Justin II (565–578).

The architects were Isidore of Miletus and Anthemius of Tralles. The construction is described by the Byzantine
historian Procopius' «Περί Κτισμάτων» (On Buildings). The emperor brought material from all over the empire and
more than 10.000 people were employed during its construction. It was decorated with marvelous mosaics.

The basilica has suffered from damage throughout the centuries. The dome collapsed completely during an
earthquake in 558 and rebuilt with lighter materials by 562. Thereafter, the new dome and its mosaic decoration
collapsed partially in many cases (fire in 859, earthquakes in 569, 989, 1344) following which they were repaired.

Upon the capture of Constantinople during the 4th Crusade, the church was ransacked and desecrated by the
Latin Christians in 1204. When the Ottoman Turks conquered Constantinople in 1453, the Hagia Sophia was
converted into the Ayasofya Mosque. Many mosaics were plastered. An extended restoration was ordered by
Sultan Abdülmecid and completed between 1847 and 1849, under the supervision of the Swiss-Italian architect
brothers Gaspare and Giuseppe Fossati. The brothers consolidated the dome and vaults, straightened the
columns, and revised the decoration of the exterior and the interior of the building. This work did not include
repairing the mosaics and after recording the details about an image, the Fossatis painted it over again. In some
cases, the Fossatis recreated damaged decorative mosaic patterns in paint, sometimes redesigning them in the
process. The Fossati intervention was executed in ochre oil paint or tempera over a lime base rendering, which
was overlaid with gold leaf and red stencilled pattern, varnished with a lacquer. In the early 1900’s, a second
intervention was carried out under the General Directorate of Pious Foundations, known as the “Vakif
intervention”. The plaster of this intervention was covered with an opaque yellow pigment in a glue medium.
Stencil ornaments in pattern double the size of Fossati’s were applied on this yellow ground

In 1932 Byzantine Institute of America, working with the Turkish government and President Mustafa Kemal
Atatürk, began the task of uncovering and restoring the surviving mosaics (many have disappeared since the
Image of the face of hexapterya figure Fossati restoration). The building reopened as a museum in 1934. The restoration was completed by1964.
courtesy of Dr. Hasan Fırat Diker
“Restoration and Conservation of Northeast Quarter of the
Main Dome and Narthex Mosaics”
Istanbul Directorate of Surveying and Monuments /
Restoration of the building and its decorations continues on by the Istanbul Directorate of Surveying and
Ministry of Culture and Tourism of Turkish Republic Monuments of the Ministry of Culture and Tourism of Turkish Republic



Hagia Sophia Dome Mosaics - Review

The characteristic areas of Hagia Sophia dome are:

 6th century mosaics
 Fossati intervention areas (1847-47)
 Vakif intervention areas (after 1910)

Original mosaic: 1000m2 =53%
Fossati: 280m2 =15%
Vakif: 560m2 =29%
Total loss: 60m2 =3%



Evaluation of the preservation state

Evaluation of the preservation state of the mosaics and the previous
interventions

Characterization of Materials Diagnosis of decay

Laboratory scale Monument scale

• Optical microscopy • IR-Thermography
• Stereomicroscopy • Ultrasonics
• Fibre Optics Microscopy • Fibre Optics Microscopy
• Scanning Electron Microscopy • Ground Penetrating Radar
• Grain Size Distribution
• Mercury Intrusion Porosimetry
• Soluble salts analysis
• Calcimetry (CO2 analysis)
• X-Ray Diffraction
• FTIR
• Thermal Analyses (DTA, TG)



Pilot panel with plastered mosaic for laboratory NDT investigation

Minor temperature Tesserae
variations are observed due 1st Rendering
to the presence of one solid
material and not a
combination of different
layers in the panel Subsurface
of Mosaic
Blank
Gold tesserae

2nd Rendering

“Hot colours” render the
presence of gold in the
investigated panel. This is
due to the low absorption
Tessera intensity (high reflection) of
the material (gold).
GE2LM
Infrared Thermography can reveal mosaics even if they are plastered

Moropoulou, A., Avdelidis, N.P., Aggelakopoulou, E., Griniezakis, S., Koui, M., Aggelopoulos, A., Karmis, P.,
Uzunoglou, N.K., “Examination of plastered mosaic surfaces using NDT techniques”, INSIGHT J. of the
British Institute of non-destructive testing, 43, No 4 (2001) pp. 241-243

Prof. Antonia Moropoulou – Topic 5.9: NDT and quality control for monitoring and compatibility assessment


Diagnostic study (Lab) – 6th cent. glass tesserae

 Bubbles on the top thin glass
layer

 Attributed to the production
technology of the tesserae,
low thaw Temperature

 Micro-cracking, micro-fissures
on the gold/silver leaves,
 whitish grains & scratches on
the top thin glass layer

Attributed to the tesserae
prolonged exposure to the
rather corrosive environment
of Hagia Sophia

Moropoulou, A., Bakolas, A., Giannoulaki, M., Karoglou, M.,
“Characterization of Dome mosaics of Hagia Sophia in
Constantinople”, Scienza e Beni Culturali XVIII, ed. G. Biscontin, G.
Driussi, Publ. Arcadia Ricerche, (2002) pp. 225-235

Moropoulou, A., Avdelidis, N.P., Delegou, E.T., Gill, C.H., Smith, J.,
“Study of deterioration mechanisms of vitreous tesserae mosaics”,
Scienza e Beni Culturali XVIII, ed. G. Biscontin, G. Driussi, Publ. Arcadia
Ricerche, (2002) pp. 843-851




Au Mapping
GOLD

SEM EDAX
SILVER

Ag Mapping

SEM EDAX
Ibid




Top thin glass layer Thick base glass
GOLD

EDAX

Top thin glass layer Thick base glass
SILVER

EDAX
Ibid




 The same production technology of glass was used for the silver and the gold glass tesserae
 The addition of CaO was not always done deliberately, but its presence was attributed to
the supplement of sand and increases the stability of glass, since it commits the free oxygen
in the network Si-O-Si.
 The Al is principally used for strengthening of the glass, since it holds the possibility of
activating the alkaline ions (Na, K), so that they cannot travel disengaged in the glass
network.
 Fe2O3 is the source of the amber hue observed in the gold tesserae, while FeO + Fe2O3 is
responsible for the greenish hue that was detected in the silver tesserae
 Light amber and greenish hue in the thick base glass resulted by the deliberate addition of
MnO, which decolourises glasses, minimising the colouring effect of accidentally
introduced iron
 EDAX confirms the existence of Au & Ag, verifying the historical data that gold & silver was
used in the production technology of the Hagia Sophia dome mosaics tesserae.

Ibid




 Setting bed mortar with two glass tesserae on the top.
On the left the “silver” glass tesserae.
 The bedding mortars were located on approximately
2-2,5m above the ring of the tympanum in the
northwest quarter of the dome of Hagia Sophia – 10th
century mosaics region.

Ibid




 Mapping images presented a homogenous distribution of the elements in the glass,
with higher percentage of silicon. The presence of Na, K is probably attributed to
the addition of ash of vegetable provenance, used for the reduction of the melting
point of the initial mixture.
 Addition of FeO+Fe2O3 resulted in the green appearance of the thick base glass,
whereas the light greenish hue is attributed to Mn presence which discolors glass.
 The EDAX analysis of the supposed silver leaf reveals an alloy of Cu, Zn, Fe and Cr
without any presence of silver. The ratio of Cu /Zn was 2/1 with a presence of Fe
and Cr in minor quantities. This type of alloy simulates the silver appearance and has
an excellent chemical stability.
 The use of this alloy is indicative of the reduced financial strength of the Byzantine
Empire in the 10th century period, verifying the historic data that report the
better quality construction of the 6th century mosaics.

Ibid



Diagnostic study (Lab) – Bedding mortars

Samples Dimensions (LxWxH-cm) Description

HgSf1 2,93 x 1,99 x 1,310 Setting bed with 2 glass tesserae, the one with
silver foil
HgSf2 3,27 x 1,41 x 1,22 Piece of mortar with straws, between setting and
intermediate bed
HgSf3 5,57 x 5,13 x 2,19 Setting bed with fresco (red ochres and black
pigment), intermediate bed
HgSf4 Small fragments of mortar of intermediate bed
mortar
HgSf5 7,72 x 5,22 x 2,98 Intermediate bed with straws
Setting bed with fresco,
intermediate bed [HgSf-3] HgSf6 3,93 x 2,65 x 2,72 Intermediate bed
HgSf7a, b a: 4,69 x 3,60 x1,72 Setting bed in two pieces
Rendering bed b : 2,04 x 1,73 x1,43

HgSf8 6,09 x 6,15 x 3,09 Intermediate bed with straws
Giannoulaki M. “Study of
HgSf9 2,00 x 1,59 x1,22 Small piece from the intermediate bed the manufacturing
technology and
assembly technique of
the Hagia Sophia dome
Macroscopic observations mosaics” Master Thesis,
Interdepartmental
Setting bed: Whitish colour / very compact Postgraduate Course
Tesserae
Intermediate bed: brown-yellowish colour / “Protection of
contains aggregates of broken monuments, sites and
complexes”, National
ceramics and straws / small Technical University of
Setting bed
pieces easily detached Athens, supervisor Prof.
Masonry
Preparative fresco: Mixture of red ochres and A. Moropoulou (2002)
black pigment
Intermediate bed




Granulometry
INTERMEDIATE BED MORTAR
 Binder / aggregate ratio ~ 1/1
 Ceramic aggregates exhibit grain distribution
shifted to >0,5mm
 Binder phase shifted to <0.5mm

Sample Composition
XRD SETTING BED MORTAR
HgSf1 Calcite, Quartz, Halite

 Main component: Calcite
HgSf3
Calcite, Quartz, Mica, Albite, Anorthite, Halite  Presence of quartz as
HgSf4 Calcite, Quartz, Albite, Anorthite, Halite, Chlorite, Hematite accessory mineral
HgSf5 Calcite, Quartz, Mica, Albite, Anorthite, Halite  Halite attributed to the
HgSf6 Calcite, Quartz, Albite, Anorthite, Halite, Dolomite effect of marine environment

HgSf8 Calcite, Quartz, Albite, Anorthite, Halite, Gypsum
HgSf9 Calcite, Quartz, Albite, Anorthite, Halite

HgSf5B Calcite, Quartz, Albite, Halite
 Calcite & quartz as above
HgSf5BE Quartz, Rosenhanite
 Presence of mical, albite and
HgSf8B Calcite, Quartz, Albite, Halite anorthite
HgSf8BE Quartz, Wollastonite Ibid




Thermogravimetry Weight loss in each temperature range (oC)
Samples CO2/H2O
SETTING BED MORTAR <120 120-200 200-600 >600
 Highest % CO2/H2O indicating (%)
mixtures of binders and HgSf1 1,07 0,35 3,19 38,24 11,98
aggregates of carbonate HgSf2 0,90 0,38 3,21 39,66 12,35
nature
 Probably, this layer was HgSf3 1,22 0,56 3,88 20,94 5,39

prepared with lime and marble HgSf3upper 1,31 0,43 3,22 39,99 12,42
powder as indicated in HgSf4 1,26 0,64 4,29 21,34 4,97
literature HgSf5 1,37 0,49 4,50 22,64 5,03
 organic substances traced 
possibly white of egg, which improves HgSf6 1,17 0,49 4,56 19,99 4,38
mechanical characteristics and HgSf7 1,30 0,63 5,18 38,34 7,40
improvement of adhesion of glass
tesserrae HgSf8 0,99 0,42 4,13 25,47 6,17

HgSf9 1,12 0,54 4,42 21,61 4,88

 The intermediate layer was prepared by slightly hydraulic lime and ceramic-sand
aggregates, with a binder/aggregate ratio of about 1/1.
 Chopped straws were added (exothermic peak at 320 oC -> organic compound
decomposition), for reinforcement and improvement of adhesion between components of
the mortar Ibid




Mercury Intrusion Porosimetry

Cum. Vol. Bulk Dens. Total Poros. Av. Pore Rad. Sp. Surf. Area
Sample
(mm3/g) (g/cm3) (%) (μm) (m2/g)

HgSf5 393.3 1.30 51.1 0.69 4.43

HgSf8 367.7 1.37 50.4 0.55 7.02

 Indicative of a lightweight mortar with high total porosity and high values
of elasticity, because of the use of ~50% ceramic-sand aggregates.
 The construction of a lightweight mortar was a necessity since the mosaics
are located at a height and under severe slope.
 Microstructural characteristics similar to those of the support structure
(bricks and masonry mortar).  Lightweight mortars were constructed with
good adhesion among their components and good cohesion to the dome
masonry.
Ibid



Total Soluble Salts and Qualitative Determination of Representative Anions

Sample S.S.T% Chlorides Sulphates Nitrates The determination of total soluble salts was
carried out according to the Normal 13/83
HgSf1 10,09 +++ - ++ and the qualitative identification of
chlorites, sulphates, and nitrates by spot
HgSf2 8,16 ++ + ++ tests

HgSf3 4,62 ++ + ++
HgSf4 4,92 + - ++
HgSf5 4,61 ++ - ++
HgSf6 4,62 + - ++
HgSf7 8,29 ++ + ++
HgSf8 4,42 + - ++
HgSf9 4,60 ++ + ++

 The setting bed mortars present the highest values of the total soluble salts attributed
to the direct environmental impact to the external layer
 Presence of chlorites is attributed to the marine environment,
 Presence of nitrates is attributed to the decomposition of organic compounds present in
the mortars.
 Presence of sulphates were identified only in a few samples in traces, probably due to the
interaction of the carbonate component of mortars with the polluted environment. Ibid



Fresco Renderings
SEM / EDAX

Oxide Composition,
s weight %

CaO 67,7

Na2O 17,9

Cl 4,6

SiO2 4,9

Fe2O3 2,5

Al2O3 1,6
Setting bed with fresco,
MgO 1,0
intermediate bed [HgSf-3]
K2 O 0,3

Total 100

 The setting bed showed remnants of red pigment on its surface, originating from the
preliminary sketches, which were usually drawn to help the mosaics workers.

 The natural earth colour, whose red color is attributed to the presence of iron oxides,
seems similar to the Byzantine Sinopean Earth.
Ibid



Diagnostic study (in-situ)
Moropoulou, A., Koui, M.,
Avdelidis, N.P., Delegou, E.T.,
Aggelakopoulou, E., Karoglou,
M., Karmis, P., Aggelopoulos,
A., Griniezakis, S., Karagianni,
E.A., Uzunoglou, N.K.,
“Investigation for the
compatibility of conservation
interventions on Hagia Sophia
mosaics using NDT
techniques”, PACT, J.
PST European Study Group on
Physical, Chemical, Biological
and Mathematical Techniques
Applied to Archaeology, 59
(2000) pp. 103-120

ET PSKT
 Located between the 19th and the 30th rib at the northwest part of the dome
 Contain 6th & 10th cent. mosaics & surfaces of Fossati & Vakif interventions



Diagnostic study (in-situ) – Surface ET

DESCRIPTION

 Characteristic surface of Vakif
intervention
 Situated between the 19th and
the 20th rib, 16m from the
centre of the dome.

AIM OF THE NDT & E

 Extent of the rendered mosaic
area
 Preservation state of the
rendered mosaic area and Vakif
interventions




Ultrasonics

Three different areas are identified in ET2 region:
 (blue) Vakif painted plaster (average velocity 1600 m/sec)
 (red) rendered mosaic (average velocity 590 m/sec)
 (black) Area with detachment or absence of tesserae (very low velocity)




Ground Penetrating Radar
ΕΤ 2
 Confirmation of ultrasonic results –
location of area of detached tesserae

 Area of increased conductivity, due to
presence of moisture and salts
 Attributed to the exfoliation of the Vakif
paint layer, revealing the decayed Fossati
gilded plaster

 the Vakif paint layer is more compact than
the lime based Fossati gilded plaster,
ΕΤ 1
resulting in the decrease of the masonry
moisture evaporation rate




Infrared Thermography

 Coated mosaic area is displayed by the darker grey areas (lower T values)
 The areas where mosaic is detached are displayed by lighter grey areas (higher
Temperature values due to different thermal diffusion rate)




Research Outcome of NDT & E on Ε Τ Surface

 Measurements demonstrated the existence of matrices of different materials
 Determination of the extent of the rendered mosaic
 Detection of the areas of detached tesserae in the rendered mosaic
 The reduction of the masonry's water-vapour permeability (moisture evaporation rate), due to the
application of the Vakif paint layer, favors phenomena like salt crystallization and detachment of
superficial layers in a polluted and highly relative humidity environment
 Consequently, this conservation intervention is considered incompatible,
 However, if the reason of the mosaics coating is to consolidate them, consolidation treatments should
be searched out through the application of bedding mortars and revealing of mosaics, according to
international deontology of revealing materials and art surfaces.



Diagnostic study (in-situ) – Surface PST

DESCRIPTION

 Joint surface of 6th and 10th
cent.m mosaics and an interface
area with Fossati restoration
plaster
 Situated between the 27th and
the 30th rib, 7m from the centre
of the dome.

AIM OF THE NDT & E

 Determination of mosaic areas
ready for detachment
 Development of the
macroscopically observed
crack on the gilded Fossati
plaster
 Evaluation of Fossati
intervention




Ultrasonics
 6th century mosaic (velocity 1650 m/sec) more compact than
10th century mosaic (velocity 1380 m/sec),

 Confirmation of historical data, that 6th century mosaics were
assembled with high quality of workmanship and technique

 Detection of local irregularities into the Fossati gilded
plaster - evidence for the distribution of the cracking,
(multiple fractured area)
 First and third areas displaying much higher velocities
(~2000 m/sec)
 Second and fourth areas corresponding to very low
velocities (358 m/sec and 500 m/sec respectively)

Area 1 (blue line): 60 – 73 cm ⇒ Sound Area
Area 2 (red line): 73 – 79 cm ⇒ Fracture
Area 3 (black line): 79 – 83 cm ⇒ Sound Area
Area 4 (green line): 83 – 87 cm ⇒ Fracture





6th century mosaic 10th century
mosaic

 Determination of fractured area at the Fossati gilded plaster region. The macroscopically observed
fracture must have been developed into a multiple fractured area.

 Location of a discontinuity (fracture / void) at the 10th century mosaic (not macroscopically observed).





10th century mosaic
Coloured tesserae show lower temperature values,
probably due to moisture presence.

Location of remains from the detached Fossati
plaster on the mosaic surface.

Fossati gilded plaster area Determination of
surface alterations - light grey areas (higher
temperature values)




Fibre Optics Microscopy

The 6th century gold tesserae present extended micro-
fractures on the gold surface (a), leading to exfoliation
and partial removal of the gold leaf (b).

(a) (b)

10th century gold tesserae similarly present partial
removal of the gold leaf, since the glass-covering layer
has been removed, while the thicker base glass seems
to be corroded (c). The blue glass tesserae suffer from
pitting corrosion (d).
(c) (d)

Micro fractures are evidenced at the gold leaf and the
red-stencilled pattern on the Fossati gilded plaster (e),
as well as surface alterations due to the varnish
oxidation. The removed gilded layer of the plaster
reveals a cracked lime substrate (f).
(e) (f)

x50 x25





(g) x25 (h) x25

 Remains of the detached Fossati plaster, among the joints of the gold tesserae and parts of
small gilded plaster, used in the Fossati conservation interventions, in order to fill in the gaps
of lost tesserae, (g)
 Straws within the plasters used in the Fossati conservation interventions are observed (g)
 The top glass of the revealed gold tesserae (after the removal of the Fossati plaster) exhibits
dulling and surface fracturing, whilst parts of the gold leaf have been detached (h)




Research Outcome of NDT & E on PSΤ Surface

 Confirmation of the historical data that 6th century mosaics were assembled with high
quality workmanship and technique, compared to 10th century mosaics,
 Identification of a deteriorated area (not macroscopically observed) in the 10th century
mosaic area,
 Determination that the macroscopically observed crack developed into a multiple
fractured area under the Fossati plaster, since such interventions were carried out for
strengthening the structure in vulnerable areas like this one (joint area of 6th and 10th
century mosaics),
 The straws within the Fossati plaster placed for reinforcement, as within the 10th century
mosaic bedding mortars, demonstrate that Fossati used traditional technology for the
preparation of plasters, i.e. a compatible conservation intervention,
 The revealed mosaic after the detachment of the Fossati plaster suffers from intense
superficial deterioration, indicating an incompatible conservation intervention.



Diagnostic study (in-situ) – Surface PSKT

DESCRIPTION

 Characteristic surface of
detached mosaic bedding
mortars from the brick
masonry, a problem that
extends in the large area
between the 25th and the
28th rib
 Situated between the 25th
and the 26th rib, 21m from
the centre of the dome.

AIM OF THE NDT & E

 Evaluation of the
preservation state of:
- the 10th century mosaic
- the Fossati restoration plaster




Ultrasonics

 Detection of superficial crack, resulting from the detached tesserae (also macroscopically observed)
 Identification of sound mosaic area (velocity of 1763 m/sec), attributed to the hydraulic lime
grouting impregnated by the UNESCO International Conservation Team (introduced from the
edges of the detached mosaic)





 Confirmation of ultrasonic results – location of superficial crack.
 Area of increased conductivity, on the Fossati restoration plaster, due to high
moisture contents and presence of salts.





Note: An interface area between the 10th century mosaic and
the Fossati restoration plaster.

The cold zone (blue coloured) is induced by rising damp and
corresponds to the Fossati restoration plastered area.

 The green coloured region (reduced temperature values compared to the rest of the mosaic) is a
mosaic area, directly affected by the transport of water and soluble salts deriving from the
plastered area.

 A void (not macroscopically observed), is also located on the top left corner of the thermograph.





Friable grey crusts, due to biological
factors, are introduced along with
crystallised salts on the tesserae
surface (a-b).

The representative black regions on
(a) x100 (b) x50 the gold mosaic tesserae arise from
the partial detachment of the gold leaf
and the corrosion of the glass layer
underneath (a-b).

Salts and exfoliated mosaic bending
mortar, which has been expanded
towards the tesserae surface due to
salts crystallisation, are presented
(c) x100 (d) x50 extensively (b).

During the Fossati conservation interventions, the gaps of lost tesserae were filled in with a varnish-
gilded plaster that also covered up healthy areas of the mosaic. The varnish oxidation initiated
prolonged decay process on the tesserae surface (c-d), inducing severe aesthetical alterations.





The moisture content and salts
crystallisation at the Fossati plaster (e),
leads to decohesion of the binding
material around the aggregates,
(e) x50 (f) x50
turning the material into a friable
surface.

Thus, plaster sections are detached (f),
leading to formation of fractures and
cavities.

(g) x50 (h) x50

The tesserae setting mark on the bending mortar (g) is attributed to the natural earth color (preparatory
fresco painting for the tesserae placement). The interaction and the binding of the restoration grout,
used by the UNESCO International Conservation Team, with the substrate of the mosaic can be observed
(h).



Diagnostic study (in-situ) - Conclusions

Research Outcome of NDT & E on Ε Τ and PSKT surfaces
 Assessment of the preservation state demonstrated the significant deterioration of the
mosaic and the Fossati plaster,

 Moisture and soluble salts were identified as the main decay factors for the Fossati plaster
and the 10th century mosaic,

 Fossati restoration plaster is the medium that permits the moisture front to move towards
the mosaic area, intensifying the moisture and soluble salts corrosive action, leading to
the deterioration and detachment of bending mortar and also the detachment of
tesserae.
 This indicates that Fossati restoration plaster can not accomplish its restoration role any
longer

What is the value of the Fossati restoration if in reality it threatens the original materials
and mosaics?

The emergency treatment of hydraulic lime grout seems to bind together the masonry and
the bedding mortar of the 10th century mosaic



In the framework

Directorate General of International Development
Cooperation - Hellenic Aid of the Hellenic Ministry of Foreign
Affairs
ELAICH – Educational Linkage Approach In Cultural Heritage

Non-destructive evaluation of
Hagia Sophia’s mosaics was performed


ELAICH Istanbul Course



Use of Ground Penetrating Radar
to assess the cohesion state of mosaics

The first mosaic area studied is
located at the perpendicular
intersection of two arches at the
south upper gallery and it
includes recently revealed The GPR scans focused on the revealed mosaic
mosaic areas, exposed brick areas, where the exterior plaster has been removed
structure and exposed stone and aimed to assess the cohesion state of the
structure. The remaining part, as mosaic with the underlying mortars and the
most of the neighboring areas is masonry structure, as well to reveal any other
covered with plaster. imperfections

A. I. Moropoulou, K. C. Labropoulos, N. S. Katsiotis “Application of ground penetrating radar for the assessment of the decay state of Hagia Sophia’s mosaics” Journal
of Materials Science and Engineering A & B, in press (2012)



An unknown zone is indicated by the white dashed
circle. The target corresponds to the space created
at the perpendicular intersection of the left arch
(stone structure) with the right arch (outer brick
structure sub-area C).

This space is possibly filled with mortar and bricks.
Care should be taken at this junction area
2.3GHz regarding the cohesion of the preserved mosaic
with its support mortar and the structure.

The target at Α11 appears to be metallic (possibly a
historic metallic pin) and is close at the stone / brick
interface. The cohesion of the tesserae with the
base mortar at the preserved arch mosaic (sub-area
A) appears to be satisfactory with no apparent
detachment of the glass tesserae layer.

Τhe mosaic preserved at sub-area A, appears to
2.3GHz have good cohesion with its support base mortar
and the arch structure.




Use of Ground Penetrating Radar
to reveal plastered mosaics

The aim was to assess the possibility of further
presence of mosaic below the plastered area and to
evaluate the risk of detachment of the mosaics
(revealed or plastered)

The second area studied is located
between two windows at the
south upper gallery.
Part of the plaster area has been
removed revealing the underlying
mosaic. External damage to the
plaster and the mosaic is observed
at the lower part of the area due to
humidity problems (from the
exterior).



1,6GHz

 In Scan A23 a mosaic layer is indicated as being
present below the plaster layer.
 A target (void space below the mosaic layer) is
indicated in the scan with a dashed curve and it is
in the same position as identified by the Hypothesis:
horizontal scan A22. This specific area was damaged in the past
 The mosaic layer does not appear to be flat. and restored by removing the material and
replacing it with new mosaic, that was
 Τhe mosaic layer appears to be in a slightly larger subsequently covered with plaster as the
depth at the start of the scan. rest of area 2
 Surface decay is observed due to humidity
The possible incompatibility (different
problems, on the exact same portion of the
compositions of the mosaic support mortars,
scanned area
or different quality of mosaic / tesserae) may
 There appears no technical reason why the be responsible for the localization of the
mosaic layer should be constructed in a larger decay phenomena at this sub-area.
depth (curved inwards),



Proposal:
Areas around the revealed mosaic where the
presence of void spaces below the plastered
mosaic layer has been identified by ground
penetrating radar

A21

A22

A25

A24

A23



Diagnosing Hagia Sophia's Historic Mosaics

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