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Conservation |
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Introduction
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| The Conservation Section's concern is with the damage that appears on the surface of the monuments and is a result of the internal structure of the marble, environmental factors and human interventions.
The works of surface conservation, are in process on all the monuments and sculptures, since 1987 and, they are in close coordination with the structural restoration programmes. They comprise a distinct project, carried out by conservators, marble technicians and conservation technicians. The scientific backbone (bedrock) for this work was provided by the extensive research carried out at the National Technical University of Athens (N.T.U.A.) by the late professor Th. Skoulikidis and his team colleagues as well as from the international literature. The methods and the materials are constantly improved through new information from the work itself and from interdisciplinary collaboration with specialists.
The main building material of the monuments is Pentelic marble, the main component of which is calcium carbonate. The foundations are of limestone.
Monochromatic surface layers are maintained on the marble surface. The layers can be distinguished in the inner "epidermis", usually orange-brown layer totally adhered to the marble and in the outer ”coating”, which is off-white and covers the "epidermis". The main components of the "epidermis" are calcium oxalate and calcium phosphate; the outer ”coating” is calcium carbonate. Inscriptions and graffities of earlier historical phases are preserved on the surface of architectural members and sculptures. Vestiges of painted decoration like red colour (hematite), blue (Egyptian blue), blue-green (malachite-azurite) and polychrome can be observed. Moreover traces of painted patterns with preliminary incisions are maintained.
The materials used in conservation are inorganic with physico-chemical and mechanical properties compatible with those of deteriorated marble. Wherever reinforcement with metal clamps or dowels is necessary, titanium is used. Organic materials have been ruled out because they have a limited life-span, they are affected by ultra-violet radiation and they are not compatible with marble.
The necessary work-site infrastructure and suitable equipment has been provided so that the works can be safely carried out. |
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General description of the marble decay: Factors and morphology |
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| The deterioration of the Pentelic marble and the foundations of the monuments is attributed to a combination of-mechanical, physico-chemical and biological factors in conjunction with the atmospheric pollution, the microclimate and the microstructure of the stone as well as the human interventions. The decay can be distinguished in the following forms: |
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"Sugaring" or granural disaggregation of marble crystals
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 This appears on surface areas directly exposed to rain fall. The rainwater acidified by carbon dioxide, sulphur dioxide and nitrogen oxides from the air pollution slowly dissolves the marble. This damage is evident in the effect on the marble crystals, leading to the loss of their cohesion and ultimately in their falling off. |
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Sulphation  The phenomenon of sulphation occurs in areas of the marble sheltered from the rain water. In the presence of moisture and sulphur dioxide the calcium carbonate, main component of the marble, is transformed into calcium sulphate dehydrate (gypsum). At first fine gypsum crystals are formed and these subsequently change into large gypsum crystals. The fine crystals layer retains the relief of the surface. |
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Deposits of air pollutants – Incrustations
 Evident in areas protected from rainwater are airborne atmospheric pollutants and suspended particles such as soot, hydrocarbons, metallic oxides that have altered the colouration of the surfaces. The black crusts are formed from successive deposits of gypsum, recrystallized calcium carbonate and various atmospheric pollutants. |
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Fractures, cracks and delamination
 Many architectural members (blocks or elements) are fractured, and subsequently their morphology and geometry have been changed. The type of failure appears either in the form of fractures, cracks or in the form of delamination, which is the splintering - breaking off of large pieces from the surface of the marble. Most of the cracks have been caused by the rusting and swelling of the iron reinforcements, mainly from the Balanos and Orlandos restoration (1890-1937). There are also fractures that are the result of mechanical forces or heat (such as earthquakes, the fire in antiquity, and the explosion of 1687). |
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Disintegration and flaking
 Disintegration and flaking are observable on areas of the surface where the marble has less coherence, so that more water penetrates and is retained. This situation is due to many factors, such as the microstructure of the marble (silicate impurities), thermal fatigue of the surface from fire, and the circulation of soluble salts from previously used conservation materials such as the Meyer cement. |
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Differential weathering  Differential weathering is the non-uniform reduction of the marble surface determined by the geological heterogeneity of the material. |
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Pitting erosion
 Pitting erosion appears in the form of semi-spherical holes either sporadically or in clusters. It is caused by the activity of micro-organisms whose development is favoured by increased humidity. It appears chiefly on the north side of the monuments and it is worse in areas with silicate veining. |
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Failure of earlier conservation interventions  In addition to the damage created by the rusting of the iron reinforcements, there are problems resulting from the mortars used in the past treatments to join fragments and to point cracks. Most are based on Sorrel or Meyer cement, which was used extensively on the monuments, including also the statues of the Acropolis, for more than 80 years. It is a white plaster with two basic components, magnesium oxide and magnesium chloride. Today, most of the mortars of this type are flaking or powdering, producing soluble salts and the adjoining marble crumbles Since 1975 when ESMA took over the coordination and supervision of the works the use of Meyer cement on the Acropolis monuments was suspended.
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Biodeterioration
 Research by microbiologists has revealed the presence of a variety of microbial colonies, consisted of bacteria, algae, fungi and lichens. The biological factor in the physico-chemical damage to the marble has been shown to be significant. Both epilithic and hasmolithic microflora alter the colour of the monuments’ surface, the secretion of erosive compounds from various micro-organisms causes the dissolution of the calcium carbonate and a large part of the microflora exerts micro-pressures resulting in surface decay. |
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| Created by V.Fotopoulos |
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