10.6092/issn.1973-9494/17308
application/pdf
1973-9494
17308
en
Mohammad Sh. Alsubaie
https://creativecommons.org/licenses/by/3.0
Conservation Science in Cultural Heritage
moisture
Weathering of monumental Islamic marble in Egypt: a contribution to heritage studies
Text.Serial.Journal
https://conservation-science.unibo.it/
22
Articles
2023-07-20
2023-06-20
2023-07-20
2023-07-20
147-170
CSCH
Mohammad Sh. Alsubaie
2022
10.6092/issn.1973-9494/17308
147
Department of Archaeology, College of Tourism and Archaeology, King Saud University, Saudi Arabia
1973-9494
moisture
en
170
Weathering of monumental Islamic marble in Egypt: a contribution to heritage studies
https://conservation-science.unibo.it/article/download/17308/16525
22
W       EATHERING OF MONUMENTAL ISLAMIC MARBLE IN
        EGYPT: A CONTRIBUTION TO HERITAGE STUDIES


   Mona M.E. Khalil, Ahmed Sallam*
   Department of Conservation, Faculty of Archaeology
   Aswan University, Aswan, Egypt

   Randa Shenouda
   Department of Conservation, Faculty of Archaeology
   Cairo University, Giza, Egypt

   Mohammad Sh. Alsubaie
   Department of Archaeology, College of Tourism and Archaeology,
   King Saud University, Saudi Arabia

   Keywords: marble, deterioration, weathering, crystallization, moisture



   1. Introduction

     Artists and builders considered colored marble as one of the everlasting and most
beautiful stones for casing the outer surfaces and lower parts of walls in historical
buildings, especially churches and mosques built during the 14th-16th centuries in Cai-
ro, the capital city of the Mamluks. Mecca and Medina (in the Hejaz region) were the
two holy cities of Islam and were annexed to the Mamluk Sultanate, so that the Mam-
luks would gain prestige as being responsible for the two holy mosques there. Howev-
er, the buildings and their marble works were not all exquisitely decorated [1]. As Egyp-
tian marble is not considered to be of the best quality, valuable decorative marble was
imported from different countries such as Italy, Cyprus and Turkey to embellish the
structures. As a result, the unique historical buildings in Cairo form a historic town
center of extraordinary value because they were built from more than one type of
stone. Indeed, marble has been used since prehistoric times in the SE Mediterranean
region for many purposes in architecture and sculpture [2-5].
     The study of the structural and decorative stones in these buildings bears witness
to extraordinary technical and artistic achievements. The variable and beautiful colors
of the marble made it a precious stone in human civilization, and it was well known
that, as a quality, color is one of the most characteristic and visible aspects in building
aesthetics and decorative stones. Color may be due to the presence of so called idio-
chromatic minerals or natural pigments present in the colored marble [6-7]; marble has
variable colors which range from white to red-yellow, brown, gray and pink, as well as
different shades of black and green. Blue calcite is very rare in marble and may be the




   * Corresponding author: dr_ahmedsalam@aswu.edu.eg
                                                                                                                           result of physical defects in the calcite which occurred during the mechanism of meta-
                                                                                                                           morphism. Natural polished limestone is sometimes called marble, but usually marbles
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                           containing >90% calcite and dolomite are considered true marbles.
                                                                                                                                Various techniques are applied to investigate the deterioration of marble and appropri-
                                                                                                                           ate methods are then used for conservation purposes; they can include a classification
                                                                                                                           system using ultrasonic means [8], physio-chemical studies using analytical techniques
                                                                                                                           such as Fourier transform infrared, X-ray diffraction and scanning electron microscopy [9],
                                                                                                                           the cleaning of marbles with laser [10], and characterization studies [11-13].
                                                                                                                                The marbles used in the construction or decoration of the historical buildings is ex-
                                                                                                                           posed to different deterioration and weathering factors (mechanical or physio-chemical
                                                                                                                           and biological) and has caused a serious decline in the state of conservation. The dete-
                                                                                                                           rioration phenomena vary greatly in the marbles present in these buildings, because
                                                                                                                           atmospheric conditions, mainly air temperature and relative humidity, differ greatly in
                                                                                                                           the interior and exterior. Weathered stones usually exhibit an increase in porosity and
                                                                                                                           water absorption, as well as a decrease in mechanical properties [14]. These aging
                                                                                                                           processes can also manifest themselves as films and external deposits. Their color
                                                                                                                           varies from black to grey, and brown to orange, and can derive from many substances
                                                                                                                           (fly-ash or other dust, biominerals formed by microbiological activity, Fe content of such
                                                                                                                           minerals, organic pigments like melanins, melaninoids, humic substances, rusty decay
                                                                                                                           products of chlorophyll) [15]. It has been mentioned in many scientific investigations
                                                                                                                           that atmospheric conditions, or the environment itself, exert a wide range of pressure on
                                                                                                                           building materials and that serious physio-chemical changes take place in the structure
                                                                                                                           and mineral constituents of these building materials due to the severe action of environ-
                                                                                                                           mental conditions, in addition to other deterioration factors.
                                                                                                                                Formation of a thick compact surficial crust is commonly observed on some arche-
                                                                                                                           ological stones resulting from the precipitation of calcite dissolved from marble and
                                                                                                                           limestone due to the attack of acidic and saline moisture [16-18].
                                                                                                                                For ancient stone monuments, the mechanisms of deterioration at archaeological
                                                                                                                           sites differ for stones buried in the soil and those that remain unburied [19-21]. Deteri-
                                                                                                                           oration of building stones buried in soil varies, depending on the temperature of the
                                                                                                                           different soil layers, soluble salts, dissolved carbon dioxide, organic matter content of
                                                                                                                           the soil, its pH value, vegetation cover, drainage conditions, hydrological status, cli-
                                                                                                                           mate, and soil structure. In poor surroundings and depending on the length of time in
                                                                                                                           the atmosphere, especially during winds and/or storms, the wetting/drying process
                                                                                                                           may result in advanced adsorption of water molecules into the grains of the marble
                                                                                                                           surfaces and may cause a reduction in strength. It also leads to the growth and open-
                                                                                                                           ing of joints (caused by stress, fatigue, hydration, drying, freezing, and thawing) and
                                                                                                                           degradation of the rock materials, as a result of water saturation (leading to dissolution,
                                                                                                                           chemical change, physical decomposition through salt crystallization) [22].
                                                                                                                                Another type of weathering is salt crystallization and recrystallization, as well as the
                                                                                                                           presence of colonies of microorganisms forming a black encrustation on the main fa-
                                                                                                                           cades of the historical buildings as a result of the attack of extensive air pollutants
                                                                                                                           present in the atmosphere, especially in Cairo. Indeed, deterioration phenomena due
                                                                                                                           to atmospheric events are examined under the main headings of freeze-thaw [23-27],
                                                                                                                           thermal shock [28-31], wetting-drying [32-34], and salt crystallization [35-37]. Biologi-
                                                                                                                           cal effects represent the direct and indirect contribution of plants, lichens, fungi, bacte-
                                                                                                                           ria, and algae to the physical and chemical disintegration of rocks [38-40]. Anthropo-
                                                                                                                           genic effects refer to the destruction caused by mechanical interventions to building
                                                                                                                           stones and the wear caused by direct human contact [41,42].


                                                                                     148
     The aim of the study is to identify and characterize the environmental parameters
causing significant variable forms of weathering in the building stones, especially mar-
ble taken from different sites, such as the architectural group of Sultan Qalawun in Al-
Muizz Al-Deen Allah Street in Cairo, and the investigation of weathered marble sam-
ples taken from marble columns inside the 14th century Qalawun mausoleum in Cairo.
This is due to the interaction of their intrinsic properties and mineral constituents with
external atmospheric conditions and the surrounding environment [43]. The objective
is to increase the awareness of decision makers about conservation actions for these
historic heritage monuments, whether the one in Cairo or similar ones in the two holy
cities in Saudi Arabia.


   2. Petrographic characteristics of marble

     Marble is considered to be a very popular metamorphic rock and highly valued due
to its exotic composition and complex fabric. Metamorphism has many definitions.
Winkler [44] has stated that metamorphism is the process which is responsible for
changes in the mineralogical and/or structural and/or chemical composition of rocks in
a solid state. But literally, metamorphism means the transformation of mineral constit-
uents and rock fabric under certain circumstances, without chemical changes to the
principal minerals, with the exception of introducing H2O and CO2 during the metamor-
phic mechanism.
     In commercial terms, the term marble refers to a flexible and versatile material that
can include rocks, such as calcium and/ or magnesium carbonate, and is called calcite
marble if it contains low levels of magnesium carbonate, which is less than 5% of its
components. Dolomitic marble is characterized by containing high levels of magnesium
carbonate, between 5% to 40% of its composition; so is ordinary limestone which, when
polished, is classified as marble. The term is often extended to include stones such as
alabaster, serpentine and other soft rocks. The quality of the marble also varies accord-




                                                                                                CONSERVATION SCIENCE IN CULTURAL HERITAGE
ing to the density of granules per cubic millimeter and we find that the higher the gran-
ularity, the higher the number per cubic millimeter; therefore the marble becomes less
porous and more resistant to water absorption, but on the other hand, if the number of
crystal particles per cubic millimeter decreases, the marble’s porosity rises and its abil-
ity to absorb water increases and the marble becomes less solid, so the marble surface
can easily crumble when exposed to humid or acidic environments [45].
      Metamorphic rocks are natural rocks existing in/ or on the Earth’s crust and make
up about 15-18 vol % of this crust; some of these rocks are named according to their
mineral constituents, such as marble. Some marbles are considered true marble where
the calcite or dolomite is > 90% quartz, garnet, feldspar, tremolite, talc, graphite, mag-
netite, etc., commonly found in these marbles.
     Marbles are characterized by different colors according to the minerals in them,
which are responsible for their pigmentation. The most famous colors range from white,
yellowish gray-beige, different shades of pink, red to brown, and greens of different
hues [46]. Carrara has a gray field or background with light gray veins and can also have
a blue-gray color.
     Scientific research reveals that there is a direct relationship between the physical
properties of stones and their internal material elements, the latter being responsible
for their physio-chemical weathering. The physical, chemical, and mechanical properties
of marbles vary greatly according to their mineral constituents, structure and the nature
of the metamorphic process.


                                                                                              149
                                                                                                                                In the renovation of the facade of some archaeological sites and cathedrals in Cairo,
                                                                                                                           Carrara marble of a light grey was used to a large extent in many parts of the building. The
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                           marble is characterized by its composition of mainly dolomite (80-90% in volume), minor
                                                                                                                           calcite (10-15% in volume) and trace minerals such as quartz, white mica, and rutile apa-
                                                                                                                           tite which are opaque minerals. The marble ranges from a homogeneous grain to a het-
                                                                                                                           erogeneous grain (average grain size 0.10 - 0.15 mm). The texture is grano-plastic with
                                                                                                                           a three-point structure; the single crystal appears lobed with irregular edges; the compo-
                                                                                                                           sition and formation of this mineral compound indicates high pressure (low temperatures
                                                                                                                           and metamorphic conditions) [47]. The most common marble is Carrara, named after
                                                                                                                           the region from which it comes. The special fame of perfect white Carrara marble is due
                                                                                                                           to the perfect combination of geology, location, topography, history and human creative
                                                                                                                           effort, resulting in an outstanding production over thousands of years, which has pro-
                                                                                                                           vided some of the finest works of art and architectural achievements in history [48].
                                                                                                                                The present research focuses on Carrara marble which was widely used in Cairo
                                                                                                                           for the construction and decoration of historical buildings. Tables 1 and 2 show that the
                                                                                                                           density and porosity values of Carrara marble are variable. One of the most important
                                                                                                                           physical properties of marble as a material is its density, which ranges from 2.6 to 2.8
                                                                                                                           g/cm3, and its compressive strength, which is typically from 50 to 100 MPa. Hardness
                                                                                                                           on the Mohs scale ranges from 3 for calcite to nearly 4 for dolomite. However, this
                                                                                                                           covers the inherent variability in grain size, the degree of crystal interlocking, and im-
                                                                                                                           perfections that can significantly affect cutting, carving and polishing. Certain impuri-
                                                                                                                           ties of a very different hardness, such as emery, quartz (e.g. grains of sand, nodules or
                                                                                                                           veins of chert) and concentrations of silicate layer minerals (clay and mica), may also
                                                                                                                           affect the usability and selectable range of work production. Kaolinite is a clay mineral
                                                                                                                           produced by the chemical weathering of aluminum silicate minerals. Clay minerals with
                                                                                                                           kaolinite are formed by the weathering or hydrothermal change of feldspars, aluminum
                                                                                                                           silicates, fine-grained elastic metamorphic rocks [49]. When feldspar is broken down by
                                                                                                                           chemical weathering, it goes through a process called hydrolysis. During hydrolysis,
                                                                                                                           the feldspar reacts with water. This causes a chemical change in the feldspar. The new
                                                                                                                           substance that is produced as a result of this chemical change is called kaolinite.

                                                                                                                           Table 1. Modal analysis (vol. %), densities, mean atomic weight (M), and cations packing index
                                                                                                                           (K- values) (Carrara marble).

                                                                                                                             Modal Analysis      Mean Matrix         Balk Density       Mean Atomic           K-Value
                                                                                                                               (vol. %)         Density g (cm3)        g (cm3)           Weight (M)

                                                                                                                            96.8 cal , 3.2dol        2.72                2.71              20.04                  5.40


                                                                                                                               Value is defined by the ratio of the pore volume (e.g. pores, open cracks) to the
                                                                                                                           volume of the whole stone sample.

                                                                                                                           Table 2. Values of porosity, water uptake and degree of saturation (Carrara marble).

                                                                                                                                 Porosity%           Mean pore radius       Water uptake (wei-        Saturation degree
                                                                                                                                                          (µm)                   ght %)                      (%)

                                                                                                                                    0.42                    0.06                    0.02                     0.90


                                                                                        150
Tables 1 and 2 show the results obtained on Carrara marble in previous studies by
Guideti (2000), Said, T. et al (2005) and Widhalm, C., et al (1996) [22,50,51]. A recent
study of Earth sciences as applied to cultural heritage highlights how the study of the
genesis and properties of the stones used in antiquities is essentially the study of the
geology of the material [52]. The documentation of these materials requires petro-
graphic studies to know their source and state of preservation in order to choose the
application of appropriate strategies for conservation purposes [47]. This type of study
needs to consider buildings and artefacts made of marble – a valuable, widely used
and traded material in ancient times – together with the use of a variety of analytical
methods [53], such as optical and scanning electron microscopy. Classifying research
on ancient marble objects is not only a subject of great archaeological importance, but
also significant due to the different aspects of conservation that need to be examined.
   Detailed examination is required to obtain reliable information about this white mar-
ble to understand whether it is from the original building or whether new Carrara mar-
ble was used to replace the old, etc. This is because in some historical buildings, the
marble is not the original at the time of construction. The marble is characterized by
dolomite (Dol 80–90% in vol) and minor quantities of calcite (10–15% in vol) with some
additional minerals such as quartz, white mica, apatite, and opaque minerals [10-12].
This is especially important because, over the past few years, studies have exposed
many works of art thought to be made of Carrara marble to be of Asian origin. Hence,
the provenance of many white marble artefacts has (or may have) been incorrectly
attributed to Göktepe and Carrara marble. Identification must involve more than just a
personal visual assessment; therefore, complex analyses are essential in order to ac-
curately study the objects and materials. Documentation on nero antico Göktepe stone
and new data on white marble sculptures of Göktepe stone, which were frequently
thought to relate to Carrara, need more than macroscopic identification based on per-
sonal eye assessments to obtain accurate information. A series of complex analyses
on the stone quarried at Göktepe are essential to study the objects correctly [54].
   A comparison between the two marbles highlights that Göktepe white is a pure cal-




                                                                                               CONSERVATION SCIENCE IN CULTURAL HERITAGE
citic marble, as is evident from its practically mono-mineral character; no accessory
minerals were noticed by optical microscopy; a minimum amount of quartz was ex-
posed by XRD. The grain size of Carrara marble appears on average coarser than that
of Göktepe marble, although MGS estimates of Göktepe white marble are frequently
similar to those for Carrara [55-57]. A multi-method approach, using a series of 11 di-
agnostic tests, based on petrography, stable isotope information and electron spin
resonance spectroscopy was used to understand the source of the white marbles and
to obtain data on the sample colour and its homogeneity, according to Attanasio, D.,
et.al [55]. The results contained the quantitative measurement of the sample colour
and its homogeneity and on this basis, we tried to differentiate the three main quarrying
basins of the Carrara district, that is, Torano, Miseglia and Colonnata. This distinction,
if based on single techniques is indefinite, but may be completed with suitable confi-
dence using a properly selected subset of six petrographic, isotopic and spectroscopic
variables that provide additional data. One study [57] looks at the organization of a
database for rock and isotope data banks, based on hundreds of analyses relating to
marble from both major quarries and small quarries. These new data allow the statisti-
cal significance of the whole database to be upgraded and new global reference isoto-
pic diagrams related to maximum grain size (MGS) of the different marbles to be
drawn, proving very useful in better determining the provenance of a given archaeolog-
ical marble object. It was on this basis that we differentiated the three main excavation
sites in the Carrara area, Torano, Miseglia and Colonnat.


                                                                                             151
                                                                                                                               Investigation of the grain size distribution is another reliable technique for distin-
                                                                                                                           guishing Carrara marble and comparing it with others. When discussing Carrara mar-
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                           ble, the public often imagines only one variety of stone. However, from a commercial
                                                                                                                           point of view, the term Carrara marble can often be too general and misleading. It has
                                                                                                                           frequently, and mistakenly, been used to describe a huge variety of different marbles
                                                                                                                           (more than 150 commercial varieties) which, with their marketable diffusion, can create
                                                                                                                           misunderstandings, since the one name ‒ Carrara Marble ‒, is given to almost any com-
                                                                                                                           mercial variation of the marble. It would, therefore, be more correct to use the term
                                                                                                                           Marmo Bianco Carrara (white Carrara marble), also named “Ordinary White”. It is typ-
                                                                                                                           ically homogeneous, and of a white ground color made up of shiny grains mixed with
                                                                                                                           grey veins which run through the stone in irregular patterns, despite the Italian adjective
                                                                                                                           bianco meaning white [58].



                                                                                                                              3. Results of experimental marble samples

                                                                                                                                Table 3 shows the water absorption value obtained in the weathered marble sam-
                                                                                                                           ple, which is 0.02 minimum and 0.40 maximum in weight % and was investigated by
                                                                                                                           the Housing & Building National Research Center (HBRC), an Egyptian agency. With
                                                                                                                           results obtained from previous studies and after conducting tests for different types of
                                                                                                                           Egyptian marble, by comparing them with our study of Carrara Marble, we came to the
                                                                                                                           following conclusions: from the results of previous studies on some Egyptian marble it
                                                                                                                           was observed that the samples of sunny marble (the commercial name for marble that
                                                                                                                           comes from El sheikh Fadl, Minya, Egypt) have reduced physical and mechanical
                                                                                                                           properties and the lowest compressive strength value (52.7 Mpa); these samples also
                                                                                                                           have the highest value of porosity (5.46), hence water absorption is high (2.12%). Also,
                                                                                                                           Teriesta marble (the commercial name for marble that comes from Wadi Wata, South
                                                                                                                           Sina, Egypt) [45], displays decent physical and mechanical properties. It has a higher
                                                                                                                           compressive strength value (79.8Mpa) with low levels of porosity (2.05), hence, water
                                                                                                                           absorption is low (0.8%).
                                                                                                                                Carrara marble samples show decent physical and mechanical properties (Table 4).
                                                                                                                           It has a high compressive strength value (Mpa) (80.2 Mpa) with the highest value of
                                                                                                                           tensile strength (5.8 Mpa) and abrasion strength (cm3/50 cm3) (22.9). Also, these sam-
                                                                                                                           ples exhibit the highest resistance to abrasion due to the presence of a higher ratio of
                                                                                                                           silica in this rock (0.72%).
                                                                                                                                Samples were tested under uniaxial compression. The uniaxial compression test
                                                                                                                           was carried out by using a computerized compression machine. The compressive
                                                                                                                           strength was obtained from the recorded value of the force divided by the cross-sec-
                                                                                                                           tional zone of the sampling [59].
                                                                                                                                The physical properties of marble, according to Reda [60], are apparent porosity,
                                                                                                                           bulk density and water absorption. Abrasion resistance was examined. The specimens
                                                                                                                           were mounted on a rotating abrasion testing machine with a rate of rotation at 38 p.m.
                                                                                                                           The loss in weight was determined after 352 revolutions. The Egyptian marble speci-
                                                                                                                           mens (sunny and Teriesta marble) were placed under a pressure of 600 gm/cm2 using
                                                                                                                           sand (25-36 mesh) as an abrasive material. There was a loss in thickness (abrasion)
                                                                                                                           in the sunny marble and Teriesta marble. All tests were carried out at the Housing &
                                                                                                                           Building National Research Center (HBRC) in Egypt, Cairo and the results for Carrara
                                                                                                                           marble are shown in Tables1-4.


                                                                                             152
    Initial porosity seriously increased due to the effects of deterioration factors and
was about 0.54٪ facilitating the penetration of moisture into the marble columns at
Qalawun, of which a sample was examined, leading to the dissolution of crystalline
salts present in the marble. It was shown that marbles, even those that are dolomitic,
are sensitive to temperature impacts. For rocks with clay minerals, the effect of tem-
perature may be responsible for shrinking [61-62]. Mineralogical studies were done by
XRD revealing that the main mineral composition of the marble was calcite, and the
additional minerals were quartz and dolomite. As regards the thermal expansion of
Carrara marble Siegsmund and Durast [61-62] stated that the average value of ther-
mal expansion is around 11x10-6 K-1 and this expansion can be classified in all cate-
gories:(a) isotropic thermal expansion without residual strain; (b) isotropic thermal ex-
pansion with residual strain; (c) and anisotropic thermal expansion with residual strain.
Compressive, tensile and abrasion values are shown in Table 4.

Table 3. Water absorption value in the weathered Carrara marble sample (weight %).

             Min                            Max                          Median

             0.02                           0.40                           0.15


Table 4. Compressive, tensile and abrasion values of Carrara marble.

 Compressive strength (Mpa)        Tensile strength (Mpa)       Abrasion strength (cm3/50
                                                                          cm3)

          80.2 (16.5)                    5.8 (19.1)                        (5.6)




                                                                                                  CONSERVATION SCIENCE IN CULTURAL HERITAGE
   4. Weathering effects

    Although metamorphic stones, especially marbles, are considered more durable
than other building materials, marbles are seriously affected by weathering factors
such as atmospheric factors and microorganisms which cause serious damage to the
mineral constituents of these stones and lead to the collapse of their physical struc-
tures. Weathering refers to the transformation and degradation of archaeological ma-
terials due to the action of the weather and regional climate; the microclimate, and
humidity and air pollution, have a crucial environmental impact in our context [63].
Moreover, discoloration is a problem in buildings, as they damage the beautiful ap-
pearance of the stone. Previous research has found that a sample of uniformly white
Carrara marble changed into a uniformly yellow-orange color when preserved with an
alkaline solution. The discoloration depended directly on the oxidation of pyrite and
hematite minerals dispersed in the marble. Although the oxidation of pyrite crystals is
a natural process, basic aqueous solutions increased the rate of oxidation [64].
    Weathering is a complex mechanism because it may result from different deterioration
factors (e.g. physio-chemical and biological). For this reason, a single type of stone can
have different deterioration patterns and the resistance of stones to different deterioration
factors vary greatly from one stone to another, depending on its nature and durability. The
most important weathering agents include air temperature, light, air humidity, air pollution
and ground moisture as well as wind, man-made deterioration factors and acid rain [65].


                                                                                                153
                                                                                                                               4.1. Natural thermal weathering
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                              Natural thermal weathering of marble is considered a very common deterioration
                                                                                                                           phenomenon resulting from a variation in air temperature which eventually leads to
                                                                                                                           dimensional changes (mechanical damage). Coarse grained marble may have signifi-
                                                                                                                           cant differences in expansion between different varieties of the same rock type. Table
                                                                                                                           5 shows the thermal expansion coefficient of marble (10-6 x k-1).

                                                                                                                           Table 5. The thermal expansion coefficient of marble (10-6 x k-1).

                                                                                                                                      Average                            Max                             Min

                                                                                                                                         11                               15                               8


                                                                                                                               Calcite, dolomite and quartz which are considered very common minerals in mar-
                                                                                                                           ble have different expansion coefficients (Table 6).

                                                                                                                           Table 6. The thermal expansion coefficient of calcite, dolomite and quartz

                                                                                                                                  Parallel to c axis            Perpendicular to c axis             Temp. Degree

                                                                                                                                   Calcite25.1x10-6                    5.6 x10-6                         0-85

                                                                                                                                 Dolomite25.8 x10-6                    6.2 x10-6                        24-700

                                                                                                                                   Quartz 7.7 x10-6                   13.3 x10-6                         0-80



                                                                                                                                               A                                   B




                                                                                                                                                            C




                                                                                                                           Figure 1. (A) Spalling and fracturing of marble column inside the courtyard of Omar Ibn Al-Aas
                                                                                                                           Mosque, Damietta, Egypt; (B) infiltration of large amounts of ground water and crystallization of
                                                                                                                           salts in historical mihrab (niche), Qalawun Mosque; (C) part of the restoration of Ottoman marble
                                                                                                                           on the southern wall of the Prophet’s Mosque in Medina.


                                                                                          154
    Changes in volume occur in marbles exposed to continuous variations in air tem-
perature in their surroundings; in this case, the marbles tend to suffer from spalling,
fracturing and separation of grains and layers (Figure 1A). These aspects of deteriora-
tion subsequently lead to an increase in porosity (called artificial porosity). The marble
elements are already exposed to temperatures of around 45- 50°C in the summer
season, but even when there are small variations in temperature, frequent heating and
cooling of the stone will finally lead to deterioration over time [66,67].


   4.2. Moisture

    Moisture content in the air (relative humidity, rainwater) and ground water are very
harmful deterioration factors that can cause serious damage to carbonate stones such
as marble. Humidity accelerates the occurrence of damage in most building materials
[68] and it is also one of the most important physicochemical factors that causes dam-
age to the surfaces of stone monuments [69].
    It can be observed that the marble slabs used for casing the lower parts of the walls
inside Qalawun (254 AH corresponding to 868 AD) tend to bow and separate from the
walls due to the penetration of large amounts of saline ground water and the crystalli-
zation of salts between these slabs and the walls. The rate of deterioration has seri-
ously increased in the last decades due to the infiltration of ground moisture in large
amounts as well as the thermal cycling (daily and seasonally) of the marble (Figure 1B).


   4.3. Relative humidity

    Relative humidity is commonly high inside Cairo’s historical buildings because of
the lack of openings. It is more than 80% in the case of the Qalawun buildings. When
this degree of relative humidity is reached inside, marble surfaces become wet due to




                                                                                                  CONSERVATION SCIENCE IN CULTURAL HERITAGE
the penetration of this humidity, which in turn leads to the recrystallization of salts on or
below the surface. An interesting phenomenon was noticed in the marble slabs, which
exhibited a tendency towards concave bowing. Several studies have tried to clarify the
phenomenon [50]. Past experiments have proved that permanent elongation can be
produced by uniformly heating marble slabs. The bowing phenomenon, however, could
only be partially reproduced [44] and stresses the fact that moisture is needed for mar-
ble slabs to buckle. Calcitic marble is more sensitive to thermal expansion than dolo-
mitic marble, since calcite crystals, when heated, show a positive expansion coefficient
on their c-axis, and a negative one perpendicular to it (Figure 1C) [70].
    Another phase of deterioration is the black discoloration (formed by a thin black layer)
of the marbles slabs due to the salty surface deposits mixed with soot; the crystalline
salts, mainly gypsum, cause several deterioration patterns in these slabs such as gran-
ular disintegration, blistering, scaling and delamination. Water and moisture are very
severe deterioration dynamics, since destructive chemical responses in archaeologi-
cal materials cannot occur without water, as the salts cannot easily dissolve and pass
into holes or pores without water (Figures 2A and B).


   4.4. Acidic rainwater

   Acidic rainwater causes severe chemical deterioration of the carbonate stones
by dissolving the mineral constituents through a chemical reaction. In interaction with


                                                                                                155
                                                                                                                           moisture, oxygen and calcium carbonate, the product of this sulfate process is the
                                                                                                                           distillation of calcium sulfate (gypsum) which resembles scales on the surface. These
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                           sulfates can be dissolved by rainwater, or they can seep into the pores of the stone, so
                                                                                                                           that a certain volume of calcium sulfate is higher than the volume of the calcium car-
                                                                                                                           bonate when recrystallized and can create enormous stress on the pore walls and an
                                                                                                                           increase in volume with peeling, leading to the damage of the stone.
                                                                                                                               The H+ – ion is responsible for the dissolution of carbonaceous materials as shown
                                                                                                                           from the following chemical formulae (1).
                                                                                                                              Ca CO3 + 2H+Ca2+ + CO2 + H2O				(1)
                                                                                                                               These minerals, such as calcite and dolomite, are considered highly soluble miner-
                                                                                                                           als compared with other minerals, such as quartz and feldspars.
                                                                                                                               The rate of the minerals’ dissolution reaction depends on:
                                                                                                                              (a) the amount and contact time of liquid water available at the mineral’s surface.
                                                                                                                              (b) The solubility of the minerals in question.
                                                                                                                              (c) The presence of acidity.
                                                                                                                               Although the mineral constituents of stones are soluble in fresh water due to the
                                                                                                                           high acidity of rainwater in Cairo’s atmosphere, these stones deteriorate as a result of
                                                                                                                           the attack of carbonic acid and sulphuric acid present in this kind of water according to
                                                                                                                           the following chemical formulae (2-5).

                                                                                                                              Ca CO3 + CO2 + H20                Ca2+ + 2 HCO3		              (2)
                                                                                                                              SO2 + H2 O → H2SO3					(3)            ←
                                                                                                                                                                    →
                                                                                                                              H2SO3 + Ca CO3 → Ca SO ½ O + CO2 + ½ H2O		                     (4)
                                                                                                                              2 Ca SO3. ½ H2O + CO2 + 3H2O → 2 Ca SO4 2 H2O                  (5)


                                                                                                                              4.5. Air pollution

                                                                                                                                                                    Air pollution is a chemical deterioration factor
                                                                                                                                                                causing serious damage to carbonate stones. It is
                                                                                                                                                                observed that the carbonate building or decorative
                                                                                                                                                                stones used in Cairo’s historical buildings have se-
                                                                                                                                                                rious deterioration phenomena resulting from air
                                                                                                                                                                pollutants. The deterioration of building stones de-
                                                                                                                                                                pends largely on climate. Many experimental stud-
                                                                                                                                                                ies have shown that temperature changes, both
                                                                                                                                                                increases and decreases, induce major deteriora-
                                                                                                                                                                tion [71]. Black particulate materials (carbon black
                                                                                                                                                                and soot) and crusts are deposited on the surfaces
                                                                                                                                                                of the historical buildings which spoil their appear-
                                                                                                                                                                ance and cover the decorative elements present on
                                                                                                                                                                their surfaces (Figure 2). These solid particulate
                                                                                                                                                                materials also play an active part in the oxidation
                                                                                                                           Figure 2A. Damaged marble of the    of gaseous pollutants such as sulfur dioxide, which
                                                                                                                           archaeological Mihrab, Ahmed Ibn    is considered a very harmful gas that causes seri-
                                                                                                                           Tulun Mosque, in Cairo, Egypt.      ous damage to carbonate building materials.


                                                                                          156
                                                       Sulphur dioxide (SO2) is an abundant
                                                   gas in Cairo, and the holy city of Mecca’s
                                                   atmosphere is highly polluted by many
                                                   sources, such as industries and heavy
                                                   traffic, which produce large quantities of
                                                   solid, liquid and gaseous pollutants.
                                                       Sulphation of carbonate stones is a
                                                   very common phenomenon in historical
                                                   buildings in Cairo and Mecca, where the
                                                   external surfaces of these stones have
                                                   layers of black encrustation which are
                                                   considered layers rich in crystalline salts,
                                                   mainly calcium sulphate (gypsum). Due
                                                   to this phenomenon marble surfaces be-
Figure 2B. A marble tombstone with kufic in-
                                                   come sugary because their mineral con-
scriptions engraved in 913 AD-1009 AD Egypt, in
the Museum of the Faculty of Archeology, Cairo     stituents have been separated and the
University. Despite its presence in the confined   physical structure has become very weak
space, the accumulation of dust and dirt on the    due to salt weathering (Figures 3A, B
surface, which hides the writing, is evident.      and C).

                                            Figure 3A. A marble column with a Corinthian crown
                                            on the entrance door illustrates the Qalawun Group,
                                            Cairo, with obvious damage to the marble surface.




                                                                                                        CONSERVATION SCIENCE IN CULTURAL HERITAGE




                                             Figure 3B. Inside Omar Ibn Al-Aas Mosque, Damietta.
                                             Salt weathering of marble.


                                            Figure 3C. Marble column with kufic inscriptions in the
                                            Grand Mosque in Mecca.


                                                                                                      157
                                                                                                                               4.6. Bio weathering
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                                Cultural heritage monuments may be stained and degraded by the growth and
                                                                                                                           activity of living organisms. As a result of the secretions of microorganisms, layers of
                                                                                                                           biofilms form on stone surfaces, causing aesthetic and structural damage. Though the
                                                                                                                           existence of biofilms on stone monuments exposed to outdoor environments is notice-
                                                                                                                           able, thin films also occur on monuments under controllable indoor environmental con-
                                                                                                                           ditions [72]. The organisms involved are bacteria, fungi, algae, and lichens [73]. Bio
                                                                                                                           weathering of monumental stones is no less dangerous than other weathering factors
                                                                                                                           where microorganisms, which are considered the most severe bio weathering factor,
                                                                                                                           can cause serious damage to stone in all climates (Figure 4).




                                                                                                                           Figure 4. Bacterial colonies growing close to the marble columns of historical mosques; algae
                                                                                                                           growth, and the spread of ground water inside the courtyard of Omar ibn Al-Aas Mosque, Damietta.


                                                                                                                             Decisive factors affecting the growth of microorganisms on or below the surface of
                                                                                                                           monumental stones are:
                                                                                                                               1) Sources of moisture which penetrate to inside the stones; it was noticed more-
                                                                                                                                  over that wet stones can retain thick colonies of microorganisms more than dry
                                                                                                                                  stones.
                                                                                                                               2) Nutrients used by microorganisms for their continued survival.
                                                                                                                               3) Stones that contain carbonate compounds that microbes live on commonly
                                                                                                                                  have thick microbial growth. Microbiological colonization producing a dark-col-
                                                                                                                                  ored crust was observed on the surface of columns and covering the marble.
                                                                                                                                  Micro-organisms play a significant and considerable role in all change process-
                                                                                                                                  es that occur in the stone.
                                                                                                                               The black fungi present on the marble surface also produce oxalic acid as a meta-
                                                                                                                           bolic product, which could have added to the formation of such a thick crust [74]. The
                                                                                                                           most effective microorganisms in the bio-weathering of monumental carbonate stones
                                                                                                                           are: bacteria, algae, lichens, and fungi.


                                                                                          158
   4.7. Bacterial species

     Bacteria are single-cell organisms, their size ranging from 1 um up to 100 um in
some bacterial species, which have the ability to exist in fissures, pores and on stone
surfaces.
    Chemoheterotrophic bacteria cause chromatic changes in the monumental stones
because they produce different organic pigments, but chemolithotrophic bacteria are
famous for producing sulfurous and sulphuric acids. The latter acid reacts with calcite
(calcium carbonate), the principal mineral in marble and produces calcium sulphate
(the organic source of calcium sulphate).
    Cyanobacteria (phototrophic bacteria) are called blue-green algae; they also cause
chromatic changes in the surface of the archaeological stones as a result of producing
different pigments.


   4.8. Fungal species

    A fungal species such as Aspergillus Niger, Alternaria etc., can form colonies of dif-
ferent colors on or below the surface of archaeological stones and also are capable of
producing severe acids which cause biodeterioration, especially for carbonate stones.


   4.9. Lichens

     Lichens cause pigmentation on the surface of archaeological stones; these surfaces
will have spots of green, gray, yellow, black, orange and pink colors.
     The microorganisms previously mentioned cause serious biodeterioration to the
carbonate stones in many ways, including physio-chemical degradation of the mineral




                                                                                               CONSERVATION SCIENCE IN CULTURAL HERITAGE
constituents; the catalytic effect of microbial metabolic activities can multiply reaction
rates enormously, as well as changes in pH by producing organic acids which enhance
mineral solubility.


   5. Materials and Methods

     About 40 specimens were collected from the most deteriorated parts of the marbles
located inside and outside the selected historical buildings: The Qalawun complex,
Cairo, and the Omar ibn Al-Aas Mosque, Damietta (see previous figures). The aim of
this widespread sampling was to cover an extensive range of weathering forms pres-
ent in these marbles. The specimens were then analyzed and investigated using the
following techniques:
   (1) X-ray diffraction (XRD): The identification of the mineral composition of the
       samples was made by X-ray diffraction patterns, using a Philips X-ray PW 1840
       diffractometer.
   (2) Scanning electron microscopy (SEM-EDX): The surface features of the dam-
       aged layers were examined by Scanning electron microscopy (SEM), (SEM
       JEOL JSM 6400) coupled with an energy dispersive X-ray spectrometer (EDS),
       to reveal details of the digenetic processes.


                                                                                             159
                                                                                                                               (3) Polarized light microscopy (PLM): The mineralogical appearance and texture
                                                                                                                                   of the marble samples were examined by using a polarized optical microscope.
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                                   Petrographic thin sections were prepared and optically analyzed by using a
                                                                                                                                   Leitz polarizing microscope.
                                                                                                                               (4) Groundwater analysis was performed by atomic absorption.


                                                                                                                               5.1. Imaging methods

                                                                                                                                Image investigation is an efficient method for illustrating the physical structure and
                                                                                                                           mineral constituents of the archaeological stone samples. Optical microscopy investi-
                                                                                                                           gations were performed by polarized light microscope (PLM) to characterize the min-
                                                                                                                           eral constituents of the marble specimens with fine grains of calcite and dolomite as
                                                                                                                           the principal minerals and the exfoliation of the sample structure, and calcite with
                                                                                                                           cracks and micro cracks. Marble samples are carbonate rocks containing both calcite
                                                                                                                           and dolomite in variable proportions, with important to moderate contents of quartz and
                                                                                                                           orthoclase. There were very dissimilar textural features. Samples from all sections
                                                                                                                           exhibited a more or less strong preparation of the shape of anisotropic grains. The
                                                                                                                           surface rocks showed enormous structures. The image in Figure 5 displays an increase
                                                                                                                           in porosity and the samples exposed more micro cracks within the thin sections. Rare
                                                                                                                           crystals of quartz and orthoclase were detected. Contact metamorphism fossil frag-
                                                                                                                           ments and iron oxide were also observed. Most of the calcite crystals were granoblas-
                                                                                                                           tic, with equidimensional shapes (pseudo-hexagonal) and different sizes.
                                                                                                                                The investigated marble samples from the Qalawun Mosque showed the presence
                                                                                                                           of calcite dolomite crystals as well as the exfoliation of the physical structure. Examina-
                                                                                                                           tion of the marble samples under polarized microscope (40X) shows the images seen
                                                                                                                           in Figures 5A and B.




                                                                                                                           Figure 5. Fragment (sample 1) from the crown of a column in the courtyard of the Qalawun
                                                                                                                           Mosque. A typical section in a marble rock under a polarizing microscope with magnification of
                                                                                                                           X40 shows interlocking calcite grains in the mosaic texture. A) Calcite and dolomite as principal
                                                                                                                           minerals and the exfoliation of the sample structure and B) calcite and cracks/ micro cracks.


                                                                                                                               Electron imaging was accomplished with SEM equipped with EDX to clarify the
                                                                                                                           deterioration aspects in the marble sample from the Qalawun Mosque. The results prove
                                                                                                                           that major deterioration is the result of the abundance of soluble salts in the rock. SEM
                                                                                                                           micrographs revealed that salt deposits on the marble surface caused several changes,
                                                                                                                           such as cracks and pores. The obtained results show that the crystalline salts played


                                                                                    160
an active role in the deterioration of this sample. Moreover, the physical structure se-
verely collapsed due to the sodium chloride and calcium sulphate. The analyses by
EDX proved that the sample of the stone from the courtyard near the Qibla (Qalawun
Mosque), consists of halite NaCl (sodium chloride) (Figures 6 and 7). Analysis of the
sample shows the elemental composition of the marble sample (Table 7).




Figure 6. Sample 2 from the column in Qalawun    Figure 7. Sample 3 from the qibla (Qalawun
Mosque shows the presence of crystalline sodi-   Mosque); the crystalline shape shows the sodi-
um chloride inside the marble sample.            um chloride salt in its ideal form of cubic crystal-
                                                 lization, indicating the stability of the salt state
                                                 and lack of continuous moisture. SEM imaging
                                                 shows the deterioration of the sample.

     5.2. Groundwater analysis

    Groundwater plays an active role in the deterioration of the building stones used in
the historical buildings in Cairo. It is considered an aggressive deterioration factor be-




                                                                                                          CONSERVATION SCIENCE IN CULTURAL HERITAGE
cause it contains Na, Cl and some other ions which cause serious damage (Table 8).

Table 7. The elemental composition of the investigated marble samples from the Qalawun Mosque.

                                                                 Compound
 No Locality    Element     Weight%    Atomic     Compound                       Intensity    Line
                                                                  Atomic%
 1    Sample   Ca          32.20       16.68      Ca Co3         80.4            17.09
      1        Na          4.22        3.18       Na Cl          10.72           0.21
               Mg          1.06        0.91       MgSO4          5.57            0.31
               Al          1.06        0.82       Al.2O2         2.00            0.26
               K           0.16        0.25       KSO4           1.60            0.38
 2    Sample   Ca          34.0        17.36      CaCO3          48.99           30.75        K
      2        Na          2.29        2.04       NaCl           5.68            0.18         K
               Ma          1.28        1.08       Mg SO4         6.34            0.26         K
               Al          1.24        0.94       Al2O           2.34            0.99         K
               K           0.41        0.22       K2O            0.50            0.59         K
 3    Sample   Ca          33.34       17.12      Ca CO3         83.47           30.03        K
      3        Na          2.28        2.52       NaCl           7.71            0. 22        K
               Ma          1.44        1.10       Al 2O3         2.73            0.58         K
               Al          1.25        1.06       MgSO4          6.20            0.26         K
               K           0.36        0.19       K2O            0.34            0.50         K



                                                                                                        161
                                                                                                                           Table 8. The elemental composition of the investigated marble samples from Qalawun
                                                                                                                           Mosque.
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                            Constituent %             Sample 1             Sample 2                Sample 3
                                                                                                                            Na    +
                                                                                                                                                       0.430                 0.370                  0.210
                                                                                                                            Ca+2                       1.510                 1.710                  1.300
                                                                                                                            Mg    +2
                                                                                                                                                       0.810                 0.750                  0.540
                                                                                                                            K+                         0.310                 0.147                  0.090
                                                                                                                            Fe +3                      0.057                 0.102                  0.021
                                                                                                                            CI-
                                                                                                                                                       0.190                 0.210                  0.085
                                                                                                                            HCO-3                      0.067                 0.080                  0.0305
                                                                                                                            SO4       -2
                                                                                                                                                       0.570                 0.910                  0.0640
                                                                                                                            CO3-2                      0.215                 0.190                  0.180
                                                                                                                            NO3       -
                                                                                                                                                       0.160                 0.185                  0.170



                                                                                                                              5.3. X – ray diffraction (XRD)

                                                                                                                               Two deteriorated samples from Qalawun Mosque of red and black marble were
                                                                                                                           analyzed by XRD. The obtained results show that calcite is the major mineral, but gyp-
                                                                                                                           sum, manganese and hematite are trace minerals in the red marble sample, whereas
                                                                                                                           calcite is the major mineral, and quartz and gypsum are trace minerals in the black
                                                                                                                           marble sample (Figure 8).




                                                                                                                                                                              Figure 8. Marble sample from Qalawun
                                                                                                                                                                              Mosque, in which calcite is the major
                                                                                                                                                                              mineral and quartz and gypsum are trace
                                                                                                                                                                              minerals (black marble).


                                                                                         162
   5.4. SEM with EDX

    Another weathered marble sample (red and white) from the qibla in the Qalawun
Mosque, was investigated by SEM equipped with EDX. The SEM image showed that
the physical structure of this sample had seriously collapsed due to the serious effect of
crystalline salts and fungi; the EDX showed the elemental composition of this sample.
                                                         A deteriorated white marble
                                                     sample taken from behind the qib-
                                                     la and mihrab of Qalawun Mosque
                                                     was also analyzed to illustrate its
                                                     elemental composition; the obtained
                                                     results are shown in Table 7. A white
                                                     marble sample, deteriorated with
                                                     microorganisms, was investigated
                                                     by SEM in order to show the phys-
                                                     io-chemical effects of these micro-
                                                     organisms. The obtained results
                                                     show that fungi can penetrate deep-
                                                     ly into marble and cause serious
Figure 9. SEM micrograph shows fungal growth inside  damage to its physical structure and
the deteriorated marble sample.                      mineral constituents (Figure 9).


   6. Conclusion

    Marble was used in large parts of the Islamic world especially in the city of Cairo
and the two holy cities of Mecca and Medina during the Mamluk period. Across the
centuries, the archaeological stones have therefore been susceptible to deterioration




                                                                                               CONSERVATION SCIENCE IN CULTURAL HERITAGE
due to the attack of weathering processes and various other deterioration factors. The
deterioration mechanism is complex because it is the result of different factors (physi-
cochemical and biological factors), the most severe factors being air pollution, varia-
tions in air temperature and relative humidity, microorganisms and acidic rainwater. In
order to assess the different deterioration factors affecting the archaeological marbles
in Egypt and determine properties, various samples were collected from marble col-
umns and decorative marble stones and investigated using different analytical meth-
ods. The obtained results showed that air temperature and relative humidity are con-
sidered vehicle factors causing serious physio-chemical damage in the marbles.
Fracturing, spalling and fissuring are very common deterioration aspects resulting from
variations in these atmospheric factors. Acidic rainwater is also responsible for the
deterioration of carbonate stones in Cairo’s historical buildings because it contains many
acids which react with the stones causing damage to their mineral constituents.
    Air pollution is also considered a very harmful deterioration factor. It plays a domi-
nant role in deteriorating the previously mentioned stones on the facades of Cairo’s
historical buildings, which are covered with black layers of soot and grease as well as
black encrustations; they also contain different kinds of salts, mainly calcium sulphate
(CaSO2*H2O) and is an indicator of the high concentration of gaseous pollutants, mainly
sulphur dioxide, in Cairo’s atmosphere. Microorganisms and other deterioration factors
such as plants, and animal and bird excrements are no less dangerous than the deterio-
ration factors previously mentioned because they play a role in the bio weathering of


                                                                                             163
                                                                                                                           carbonate stones. Most of the microbial species are responsible for alterations in the
                                                                                                                           pigmentation (chromatic changes) of the original surface of the stones; moreover, these
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                           microorganisms, especially bacteria and lichens, are considered producers of acids such
                                                                                                                           as oxalic, carbonic and sulphuric acids. Therefore, the crusts present on the surface of the
                                                                                                                           carbonate stones contain crystalline salts such as calcium oxalate and calcium sulphate.


                                                                                                                                 Acknowledgements

                                                                                                                               The authors wish to thank Prof. Dr. Mohamed Abd EL Hady, Faculty of Archaeolo-
                                                                                                                           gy, Cairo University, Giza, Egypt and Prof. Ioannis Liritzis for their constructive com-
                                                                                                                           ments. The author would like to mention the support from Prof. Mona F. Ali, Head of the
                                                                                                                           restoration department, Faculty of Archaeology, Cairo University, Egypt.


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                                                                                                                              Biographical notes

                                                                                                                               Mona M.E. Khalil is an assistant professor fellow at the Conservation Department
                                                                                                                           of the Faculty of Archaeology at Aswan University. Her research interests are gypsum
                                                                                                                           masks, stones, advanced technologies, and conservation of museum pieces.

                                                                                                                               Ahmed Sallam is an associate professor fellow at the Conservation Department of
                                                                                                                           the Faculty of Archaeology at Aswan University. He received a scholarship from Eras-
                                                                                                                           mus Munds at the Department of Materials and Nano Physics, Royal Institute of Tech-
                                                                                                                           nology KTH Stockholm, Sweden in 2014-2015. His research interests are in mural
                                                                                                                           painting, stones and advanced technologies in the field of cultural heritage.

                                                                                                                               Randa Shenouda is a Conservator in the Department of Conservation at the Fac-
                                                                                                                           ulty of Archaeology at Cairo University. Her research interests are stones, advanced
                                                                                                                           technologies, and conservation of archaeological buildings.

                                                                                                                              Mohammad Sh. Alsubaie is an assistant professor in the Department of Archae-
                                                                                                                           ology, College of Tourism and Archaeology, at King Saud University, Saudi Arabia. He


                                                                                      168
is interested in archaeological and historical studies in various fields and countries. He
has contributed to collecting historical information and archaeological analyses.

   Summary

    Marble is a metamorphic rock widely used in historical buildings as a structural
and decorative stone; also, it is commonly used for sculpture and as a building ma-
terial; for example, the lower parts of many walls of Mamluk and Turkish buildings are
covered with marble tiles of different colors (mainly, white, red, black) as well as
many of the columns in these structures. Due to the severe effects of deterioration
factors, such as, atmospheric parameters, air pollution, ground water, micro-organ-
isms, the decorative marble slabs and columns are seriously deteriorated. Forty mar-
ble specimens were collected from the most deteriorated parts of marbles located
inside and outside selected historical buildings, namely the Sultan Qalawun complex
in Al-Muizz Al-Deen Allah Street in Cairo (1284 AD) an archaeological architectural
group, built in the Mamluk style. The present work focuses on the identification of the
mechanism of marble deterioration. In order to carry out this study, different samples
were collected from the deteriorated historical marble of the Qalawun; the marble
samples collected for study were not from a single building, but from the complex of
the Sultan Qalawun Group or the Qalawun Mosque, and included a school and
dome, and the Mosque. The mihrab of the dome is considered one of the most luxu-
rious mihrabs of antiquity in Egypt. Each of its sides is surrounded by three marble
columns, and its cavity has four layers of gilded recesses supported by marble col-
umns. The marble samples were investigated by X-ray diffraction (XRD), X-ray fluo-
rescence (XRF), polarized light microscope (PLM) and scanning electron microscope
with energy dispersive x-ray spectroscopy (SEM-EDS). The obtained results showed
that the mineral constituents of the investigated samples were seriously deteriorated,
and the physical structure had collapsed.




                                                                                                  CONSERVATION SCIENCE IN CULTURAL HERITAGE
   Riassunto

     Il marmo è una roccia metamorfica molto utilizzata negli edifici storici come pietra
strutturale e decorativa; inoltre, è comunemente usato per la scultura e come mate-
riale da costruzione: ad esempio, le parti inferiori di molte pareti di edifici mamelucchi
e turchi sono ricoperte da piastrelle di marmo di diversi colori (principalmente bianco,
rosso, nero) così come molte delle colonne di queste strutture. A causa dei gravi ef-
fetti dei fattori di degrado, quali parametri atmosferici, inquinamento atmosferico,
acque sotterranee, microrganismi, le lastre e le colonne decorative in marmo sono
gravemente deteriorate. Quaranta campioni di marmo sono stati raccolti dalle parti
più deteriorate di marmi situati all’interno e all’esterno di edifici storici selezionati, in
particolare il complesso Sultan Qalawun in Al-Muizz Al-Deen Allah Street al Cairo
(1284 d.C.) un gruppo architettonico archeologico, costruito in stile mamelucco . Il
presente lavoro si concentra sull’identificazione del meccanismo di deterioramento
del marmo. Per realizzare questo studio sono stati prelevati diversi campioni dal
marmo storico deteriorato del Qalawun; i campioni di marmo raccolti per lo studio
non provenivano da un singolo edificio, ma dal complesso del Sultan Qalawun Group
o dalla Moschea Qalawun, e comprendevano una scuola, una cupola e la Moschea.
Il mihrab della cupola è considerato uno dei mihrab più lussuosi dell’antichità in Egit-
to. Ciascuno dei suoi lati è circondato da tre colonne di marmo e la sua cavità ha


                                                                                                169
                                                                                                                           quattro strati di rientranze dorate sostenute da colonne di marmo. I campioni di mar-
                                                                                                                           mo sono stati studiati mediante diffrazione di raggi X (XRD), fluorescenza a raggi X
Mona M.E. Khalil, Ahmed Sallam, Randa Shenouda, Mohammad Sh. Alsubaie - Weathering of monumental islamic marble in Egypt




                                                                                                                           (XRF), microscopio a luce polarizzata (PLM) e microscopio elettronico a scansione
                                                                                                                           con spettroscopia di raggi X a dispersione di energia (SEM-EDS). I risultati ottenuti
                                                                                                                           hanno mostrato che i costituenti minerali dei campioni indagati erano gravemente
                                                                                                                           deteriorati e la struttura fisica era crollata.




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