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Soiling and Blackening in archaeological sites and monuments of Iranian Cultural HeritagePresentation Transcript
Soiling and Blackening in archaeological sites and monuments of Iranian Cultural Heritage A. Bonazza, C. Sabbioni, N. Ghedini, B. Hermosin, C. Saiz-Jimenez Heritage, Weathering & Conservation Madrid, 21-24 June 2006
SOILING AND BLAKENING……. Anthropogenic origin: Black crusts are observed mainly on carbonate stones surfaces wetted by rainwater but sheltered from intensive runoff and wash out. They are due to the dry an wet deposition of SO 2 and carbon particles . Biogenic origin: Black patinas produced by the transformation of microorganisms colonizing monument surfaces Urban areas R ural and urban areas
Gulf War – Effect of the Kuwait oil fires in 1991 Peter V. Hobbs and Lawrence F. Radke, 1992. Airborne Studies of the Smoke from the Kuwait Oil Fires. Science 256, 987-991. Spring 1991: burning of ~4.6 million barrels of oil per day Individual fires produced different plumes, ranging from black to white The intensity of the fires made combustion relatively efficient with about 96% of the carbon burned emitted as CO 2 and with very low emissions of CO and soot
RESULTS The building materials at all the archaeological sites investigated are metamorphic and sedimentary carbonate stones XRD analysis Presence of brown coloured surface layer: secondary calcite, quartz, sheet silicates and Fe oxides OM-XRD
RESULTS Surface inter-crystalline decohesion due to wind erosion produced by the impact of airborne soil dust (quartz-calcite) Biological colonisation SEM-EDX
RESULTS NCC = OC + EC Chemical-thermal analysis for carbon fractions speciation and measurement ( Ghedini et al. 2006 ) OC : biological wheatering atmospheric pollution organic treatments decay EC: carbonaceous particles IC-CHNSO Sulphates in black crusts on monuments located in European cities: 52 – 542 · 10 3 μg/g ( Bonazza et al. 2005 )
RESULTS GC-MS n -Heptadecane n -Heptadecane n -Tetradecanoid acid methyl ester n -Heptadecane n -Tetradecanoid acid methyl ester Metyl pentadecanoid acid methyl ester Metyl pentadecanoid acid methyl ester Metyl pentadecanoid acid methyl ester n -Hexadecanoid acid methyl ester n -Hexadecanoid acid methyl ester n -Hexadecanoid acid methyl ester n -Hexadecanoid acid methyl ester Octadecenoic acid methyl ester Octadecenoic acid methyl ester Octadecadienoic acid methyl ester Persepolis Pasargadae Firooz Abad Izeh Reliefs The organic fraction is composed of a complex mixture of aliphatic compounds, mainly represented by n -fatty acids and n-alkanes as minor compounds Heptadecane is a predominant constituent of most cyanobacteria and algae No aromatic hydrocarbons indicating fossil fuel combustion
A: TIC B: ion fragmentogram obtained using high resolution SIM-mode. Distribution pattern of the series of n -alkanes (m/z 85) with preference index of 1 RESULTS GC-MS Methyl pentadecanoic acid methyl ester n -Hexadecanoic acid methyl ester Octadecenoic acid methyl ester n -Octadecanoic acid methyl ester n -Heptadecane n -Tetradecanoic acid methyl ester Methyl Pentadecanoic acid methyl ester n -Hexadecanoic acid methyl ester C 23 C 34 Aliphatic hydrocarbons C 23 – C 34 Bishapour Bishapour Evidence of a cyanobacterial biopolymer contribution
Inter-crystalline decohesion, due to wind erosion, surface oxidation and blackening are the main damage typologies encountered at the Iranian archaeological sites under study.
The low concentrations for sulphates, the presence of oxalates and the major presence of n -fatty acids and the absence of typical tracers of fossil fuels combustion in the organic fraction points to a major biological contribution of phototrophic microorganisms for the soiling encountered.
The desiccation/senescence of cyanobacteria colonizing stones leads to a blackening of the surface, mainly because of chemical changes in the nucleic acids and lipid components such as chlorophyll, and the oxidation of unsaturated fatty acids accumulating in the cells.